Review: Shadow Scale, by Rachel Hartman

Series:	Seraphina #2
Publisher:	Ember
Copyright:	2015
ISBN:	0-375-89659-7
Format:	Kindle
Pages:	458

Shadow Scale, despite confusing publisher marketing that calls it a "companion" to Seraphina, is a direct sequel. It picks up shortly after Seraphina and resolves most of the loose ends of the previous book. This is a book for which my completionist tendencies did me no favors. The book I was intending to read, when I started on Hartman's work, is Tess of the Road, but I hate starting series in the middle and it was clear that Tess was set after Seraphina. (I have been repeatedly assured that this doesn't matter and that one can start with Tess. Such reassurances rarely work on me; do as I say, not as I do.) For Seraphina itself, this turned out fine; I'm mildly surprised by the book's Andre Norton award nomination, but it was enjoyable enough and I liked the first-person protagonist. Shadow Scale I approached with a bit more trepidation. I hadn't heard much about it and the few reviews I saw were lukewarm. Unfortunately, there's a reason for that. Seraphina left obvious room for a sequel, including a brewing war, significant unresolved interpersonal relationships, and Seraphina's own newfound understanding of the nature of her internal menagerie. Alas, the start of the book uses the war primarily as plot device (and introduces a brand-new bit of magic that I never found interesting), largely ignores the relationship, and focuses on that third plot element. And by focuses, I mean Seraphina is sent out of the country of Goredd on a journey of map exploration to collect plot coupons. The best description I have for the middle of this book is tedious and depressing. Like a lot of novels, it has a U-shaped plot: things get worse and worse until a crisis, and then start getting better. This plot can work, but the reader has to have a good reason to stick through the depressing bits. One of the better reasons is if the plot allows the main character some small triumphs, maintaining their agency throughout even if larger events are spiraling out of control. This is not one of those books. After some early successes tracking down some objects of her search, Seraphina encounters an antagonist from her own past (barely hinted at in the first book) who can systematically corrupt everything she is trying to do. She spends most of the book feeling like what she's doing is futile, or hoping for things the reader knows aren't going to happen. Given that this is happening during plodding map exploration fantasy through largely indistinguishable faux-medieval countries, or (later) somewhat more interesting but obviously irrelevant local politics in a remote trading city, it's hard to avoid sharing that sense of futility. The other structural problem with Shadow Scale is that the plot coupons are people, which means this book has an excessive cast size problem. Seraphina collects too many people for me to even keep straight, let alone care about. Critical developments (usually for the worst) in the lives of one of these characters were frequently met with reader mutterings like, "Now which one was Brasidas again, was he the plague doctor?" This tends to undermine the emotional impact. It didn't help that the plot was enough of a slog that I kept putting the book aside for a few days. This does get better, but not enough better to redeem the middle of the book, and one has to put up with a lot of helpless despair to get there. Shadow Scale is one of those stories where the protagonist has the innate power to resolve the plot, is told cryptically by various people that this is the case, but has absolutely no idea how to use it and her supposed mentors are essentially useless. The result is that she feels both hopeless and guilty, which was not the reading experience I wanted. I did enjoy the moment when she finally figures it out, and I thought Hartman's idea was reasonably clever, but it would have been better if that had happened faster. Like, 200 pages faster. At least. The major world-building in Seraphina was the dragons. The dragons also show up in this book (and feel less like autism spectrum archetypes, which I appreciated), and in theory are central to the plot, but I'm not entirely sure why? It was an odd reading experience. I think Hartman was attempting to set up dual villains posing different threats, but the dragon one is off-screen for nearly the entire book and never developed, so it feels perfunctory. Near the end of the book, Hartman abruptly picks up the dragons again, but that whole section felt oddly disconnected from the rest of the plot and is only barely relevant to the resolution. At least for me, the plot structure didn't cohere. Shadow Scale does go up a whole point in rating for me because of the romance plot and how Hartman resolves it, which I will not spoil but which I loved. The process of getting there is immensely frustrating because it feels like Hartman is forcing the characters into a corner where only stupid resolutions are possible, but in this case the U-shaped emotional structure worked on me. The ending is completely true to the characters in a way that I thought Hartman had made impossible (and which does a lovely bit of undermining of traditional roles), so full credit there. It helped that the relationship is put on ice for most of the book and only appears at the end (which is also the best part of the book), so it didn't drag on like the other parts of the plot. Overall, though, I tentatively agree with the general advice to skip this one, and suspect that advice will become less tentative once I read Tess of the Road. It's a largely unpleasant slog. There are some mildly interesting world-building revelations that fill in the background of Seraphina, the ending was reasonably good, and the relationships were much better than I was expecting through most of the book, but the amount of time and patience required to get there was not a good trade-off for me. Followed (in the sense that it's set in the same universe but is not a sequel and I suspect does not depend heavily on this plot) by Tess of the Road. Rating: 4 out of 10

The Rcpp team is pleased to announce release 1.0.7 of Rcpp which arrived at CRAN earlier today, and will be uploaded to Debian shortly. Windows and macOS builds should appear at CRAN in the next few days. This release continues with the six-months cycle started with release 1.0.5 last July. As a reminder, interim dev or rc releases will alwasys be available in the Rcpp drat repo; this cycle there were seven (!!). These rolling release tend to work just as well, and are also fully tested against all reverse-dependencies. Rcpp has become the most popular way of enhancing R with C or C++ code. As of today, 2323 packages on CRAN depend on Rcpp for making analytical code go faster and further, along with 227 in BioConductor. This release contains a change which Luke Tierney urged us to make a good year ago in #1081) (and which we had looked at earlier in #382). Implementing the change in a regular update proved a little tricky, and my initial branch lay dormant until I aki revived it, and finished the transition (which we then did in two PRs). The change concerns how Rcpp grows internal objects, and the new approach (thanks to the hint by Luke) closer to what R does guaranteeing linear behaviour. It turns out that we overlooked one aspect (of coping with Modules built under earlier Rcpp releases) so the initial upload to CRAN on Saturday revealed that we needed a small adjustment that we made for the final release. This version should now be more performant, and rest on a stable API. Based on the reverse depends checks by both us and CRAN (using the updated version), we expect no issues with existing code. However, it something does act up a fresh compilation of the packages using Rcpp may help. We also made a few other minor changes in the API such as silencing a silly compiler warning, ensuring global Rcout and Rcerr objects, adding support for a new Rcpp::message() call, completing a switch to uint32_t instead of unsigned int and including the cfloat header (which relates to STRICT_R_HEADERS discussed below). Similarly, the Rcpp Attributes feature was enhanced by coping better with packages with a dot in their name and their for per-package include files, along with support for more quiet compilation if desired. As some Rcpp users may have seen, we plan to enable STRICT_R_HEADERS by the next release (expected in January 2022). A long issue tick #1158 is laying the ground work. Maintainers of 81 packages which are affected and need a small change (such as for example switching from PI to M_PI); of these 56 have already responded. We plan to be in touch in the fall. Adding the cfloat header is one help in this transition (as the corresponding C header was pulled in when STRICT_R_HEADERS is not defined) as it ensures DBL_EPSILON and alike are defined. Last but not least this is also the first relase in which we welcome I aki as a new member of the Rcpp Core team. Yay! The NEWS file entries follow summarizing the nine key PRs in this release.

Changes in Rcpp release version 1.0.7 (2021-07-06)

• Changes in Rcpp API:
  • Refactored Rcpp_PreserveObject and Rcpp_ReleaseObject which are now O(1) (Dirk and I aki in #1133 and #1135 fixing #382 and #1081).
  • A spuriously assigned variable was removed (Dirk in #1138 fixing #1137).
  • Global Rcout and Rcerr objects are supported via a compiler directive (I aki in #1139 fixing #928)
  • Add support for Rcpp::message (Dirk in #1146 fixing #1145).
  • The uint32_t type is used throughout instead of unsigned int (Dirk in #1153 fixing #1152).
  • The cfloat header for floating point limits is now included (Dirk in #1162 fixing #1161).
• Changes in Rcpp Attributes:
  • Packages with dots in their name can now have per-package include files (Dirk in #1132 fixing #1129).
  • New argument echo to quieten optional evaluation in sourceCpp (Dirk in #1138 fixing #1126).
• Forthcoming Changes in Rcpp API:
  • Starting with Rcpp 1.0.8 anticipated in January 2022, STRICT_R_HEADERS will be enabled by default, see #1126.

Thanks to my CRANberries, you can also look at a diff to the previous release. Questions, comments etc should go to the rcpp-devel mailing list off the R-Forge page. Bugs reports are welcome at the GitHub issue tracker as well (where one can also search among open or closed issues); questions are also welcome under rcpp tag at StackOverflow which also allows searching among the (currently) 2616 previous questions. If you like this or other open-source work I do, you can sponsor me at GitHub.

This post by Dirk Eddelbuettel originated on his Thinking inside the box blog. Please report excessive re-aggregation in third-party for-profit settings.

Ten years ago I began the olduse.net exhibit, spooling out Usenet history in real time with a 30 year delay. My archive has reached its end, and ten years is more than long enough to keep running something you cobbled together overnight way back when. So, this is the end for olduse.net. The site will continue running for another week or so, to give you time to read the last posts. Find the very last one, if you can! The source code used to run it, and the content of the website have themselves been archived up for posterity at The Internet Archive. Sometime in 2022, a spammer will purchase the domain, but not find it to be of much value. The Utzoo archives that underlay it have currently sadly been censored off the Internet by someone. This will be unsuccessful; by now they have spread and many copies will live on.

---

I told a lie ten years ago.

You can post to olduse.net, but it won't show up for at least 30 years.

Actually, those posts drop right now! Here are the followups to 30-year-old Usenet posts that I've accumulated over the past decade. Mike replied in 2011 to JPM's post in 1981 on fa.arms-d "Re: CBS Reports"

A greeting from the future: I actually watched this yesterday (2011-06-10) after reading about it here.

Christian Brandt replied in 2011 to schrieb phyllis's post in 1981 on the "comments" newsgroup "Re: thank you rrg"

Funny, it will be four years until you post the first subnet post i ever read and another eight years until my own first subnet post shows up.

Bernard Peek replied in 2012 to mark's post in 1982 on net.sf-lovers "Re: luke - vader relationship"

i suggest that darth vader is luke skywalker's mother.

You may be on to something there.

Martijn Dekker replied in 2012 to henry's post in 1982 on the "test" newsgroup "Re: another boring test message" trentbuck replied in 2012 to dwl's post in 1982 on the "net.jokes" newsgroup "Re: A child hood poem" Eveline replied in 2013 to a post in 1983 on net.jokes.q "Re: A couple"

Ha!

Bill Leary replied in 2015 to Darin Johnson's post in 1985 on net.games.frp "Re: frp & artwork" Frederick Smith replied in 2021 to David Hoopes's post in 1990 on trial.rec.metalworking "Re: Is this group still active?"

Host to Kanchenjunga, the world s third-highest mountain peak and the endangered Red Panda, Sikkim is a state in northeastern India. Nestled between Nepal, Tibet (China), Bhutan and West Bengal (India), the state offers a smorgasbord of cultures and cuisines. That said, it s hardly surprising that the old spice route meanders through western Sikkim, connecting Lhasa with the ports of Bengal. Although the latter could also be attributed to cardamom (kali elaichi), a perennial herb native to Sikkim, which the state is the second-largest producer of, globally. Lastly, having been to and lived in India, all my life, I can confidently say Sikkim is one of the cleanest & safest regions in India, making it ideal for first-time backpackers.

---

Reaching Sikkim

• Gangtok, being the capital, is easiest to reach amongst other regions, by public transport and shared cabs.
• By Air:
  • Pakyong (PYG) :
    • Nearest airport from Gangtok (about 1 hour away)
    • Tabletop airport
    • Reserved cabs cost around INR 1200.
    • As of Apr 2021, the only flights to PYG are from IGI (Delhi) and CCU (Kolkata).
  • Bagdogra (IXB) :
    • About 20 minutes from Siliguri and 4 hours from Gangtok.
    • Larger airport with flights to most major Indian cities.
    • Reserved cabs cost about INR 3000. Shared cabs cost about INR 350.
• By Train:
  • New Jalpaiguri (NJP) :
    • About 20 minutes from Siliguri and 4 hours from Gangtok.
    • Reserved cabs cost about INR 3000. Shared cabs from INR 350.
• By Road:
  • NH10 connects Siliguri to Gangtok
  • If you can t find buses plying to Gangtok directly, reach Siliguri and then take a cab to Gangtok.
• Sikkim Nationalised Transport Div. also runs hourly buses between Siliguri and Gangtok and daily buses on other common routes. They re cheaper than shared cabs.
• Wizzride also operates shared cabs between Siliguri/Bagdogra/NJP, Gangtok and Darjeeling. They cost about the same as shared cabs but pack in half as many people in luxury cars (Innova, Xylo, etc.) and are hence more comfortable.

---

Gangtok

• Time needed: 1D/1N
• Places to visit:
  • Hanuman Tok
  • Ganesh Tok
  • Tashi View Point [6,800ft]
  • MG Marg
  • Sikkim Zoo
  • Gangtok Ropeway
  • Enchey Monastery
  • Tsuklakhang Palace & Monastery
• Hostels: Tagalong Backpackers (would strongly recommend), Zostel Gangtok
• Places to chill: Travel Cafe, Caf Live & Loud and Gangtok Groove
• Places to shop: Lal Market and MG Marg

Getting Around

• Taxis operate on a reserved or shared basis. In case of the latter, you can pool with other commuters your taxis will pick up and drop en-route.
• Naturally shared taxis only operate on popular routes. The easiest way to get around Gangtok is to catch a shared cab from MG Marg.
• Reserved taxis for Gangtok sightseeing cost around INR 1000-1500, depending upon the spots you d like to see
• Key taxi/bus stands :
  • Deorali stand: For Darjeeling, Siliguri, Kalimpong
  • Vajra stand: For North & East Sikkim (Tsomgo Lake & Nathula)
  • Rumtek taxi: For Ravangla, Pelling, Namchi, Geyzing, Jorethang and Singtam.

Exploring Gangtok on an MTB

• If you'd like to explore Gangtok at your own pace, you could rent a cycle from Hub Outdoor or HillBike. I paid INR 600 for a day at HillBike.
• These are well-maintained geared mountain bikes, so adapting to inclines and declines should be a breeze, even for beginners.
• Cycling down from Ganesh Tok to Tashi View Point is an absolute delight and in my opinion, the best thing you can do in Gangtok.
• While it is a little unconventional and exhausting (uphill stretches), but a 100% recommended unless you ve been skipping leg day
• Pro tip : Make sure you use the right/back brake while decelerating downhill and not the left/front brake.
• Recommended route [3-5hrs, 20.3Km, 1770-2081ft] : Chandmari (HillBike) -> Sera Jhe Dro-Phen-Ling Monastery > Ganesh Tok > Tashi View Point > Bakthung Falls > Vajra Stand > Tsuklakhang Palace & Monastery > Enchey Monastery > Chandmari

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North Sikkim

• The easiest & most economical way to explore North Sikkim is the 3D/2N package offered by shared-cab drivers.
• This includes food, permits, cab rides and accommodation (1N in Lachen and 1N in Lachung)
• The accommodation on both nights are at homestays with bare necessities, so keep your hopes low.
• In the spirit of sustainable tourism, you ll be asked to discard single-use plastic bottles, so please carry a bottle that you can refill along the way.
• Zero Point and Gurdongmer Lake are snow-capped throughout the year

3D/2N Shared-cab Package Itinerary

• Day 1
  • Gangtok (10am) - Chungthang - Lachung (stay)
• Day 2
  • Pre-lunch : Lachung (6am) - Yumthang Valley [12,139ft] - Zero Point - Lachung [15,300ft]
  • Post-lunch : Lachung - Chungthang - Lachen (stay)
• Day 3
  • Pre-lunch : Lachen (5am) - Kala Patthar - Gurdongmer Lake [16,910ft] - Lachen
  • Post-lunch : Lachen - Chungthang - Gangtok (7pm)
• This itinerary is idealistic and depends on the level of snowfall.
• Some drivers might switch up Day 2 and 3 itineraries by visiting Lachen and then Lachung, depending upon the weather.
• Areas beyond Lachen & Lachung are heavily militarized since the Indo-China border is only a few miles away.

---

East Sikkim

Zuluk and Silk Route

• Time needed: 2D/1N
• Zuluk [9,400ft] is a small hamlet with an excellent view of the eastern Himalayan range including the Kanchenjunga.
• Was once a transit point to the historic Silk Route from Tibet (Lhasa) to India (West Bengal).
• The drive from Gangtok to Zuluk takes at least four hours. Hence, it makes sense to spend the night at a homestay and space out your trip to Zuluk

Tsomgo Lake and Nathula

• Time Needed : 1D
• A Protected Area Permit is required to visit these places, due to their proximity to the Chinese border
• Tsomgo/Chhangu Lake [12,313ft]
  • Glacial lake, 40 km from Gangtok.
  • Remains frozen during the winter season.
  • You can also ride on the back of a Yak for INR 300
• Baba Mandir
  • An old temple dedicated to Baba Harbhajan Singh, a Sepoy in the 23rd Regiment, who died in 1962 near the Nathu La during Indo China war.
• Nathula Pass [14,450ft]
  • Located on the Indo-Tibetan border crossing of the Old Silk Route, it is one of the three open trading posts between India and China.
  • Plays a key role in the Sino-Indian Trade and also serves as an official Border Personnel Meeting(BPM) Point.
  • May get cordoned off by the Indian Army in event of heavy snowfall or for other security reasons.

---

West Sikkim

• Time needed: 3N/1N
• Hostels at Pelling : Mochilerro Ostillo

Itinerary

Day 1: Gangtok - Ravangla - Pelling

• Leave Gangtok early, for Ravangla through the Temi Tea Estate route.
• Spend some time at the tea garden and then visit Buddha Park at Ravangla
• Head to Pelling from Ravangla

Day 2: Pelling sightseeing

• Hire a cab and visit Skywalk, Pemayangtse Monastery, Rabdentse Ruins, Kecheopalri Lake, Kanchenjunga Falls.

Day 3: Pelling - Gangtok/Siliguri

• Wake up early to catch a glimpse of Kanchenjunga at the Pelling Helipad around sunrise
• Head back to Gangtok on a shared-cab
• You could take a bus/taxi back to Siliguri if Pelling is your last stop.

---

Darjeeling

• In my opinion, Darjeeling is lovely for a two-day detour on your way back to Bagdogra/Siliguri and not any longer (unless you re a Bengali couple on a honeymoon)
• Once a part of Sikkim, Darjeeling was ceded to the East India Company after a series of wars, with Sikkim briefly receiving a grant from EIC for gifting Darjeeling to the latter
• Post-independence, Darjeeling was merged with the state of West Bengal.

Itinerary

Day 1 :

• Take a cab from Gangtok to Darjeeling (shared-cabs cost INR 300 per seat)
• Reach Darjeeling by noon and check in to your Hostel. I stayed at Hideout.
• Spend the evening visiting either a monastery (or the Batasia Loop), Nehru Road and Mall Road.
• Grab dinner at Glenary whilst listening to live music.

Day 2:

• Wake up early to catch the sunrise and a glimpse of Kanchenjunga at Tiger Hill. Since Tiger Hill is 10km from Darjeeling and requires a permit, book your taxi in advance.
• Alternatively, if you don t want to get up at 4am or shell out INR1500 on the cab to Tiger Hill, walk to the Kanchenjunga View Point down Mall Road
• Next, queue up outside Keventers for breakfast with a view in a century-old cafe
• Get a cab at Gandhi Road and visit a tea garden (Happy Valley is the closest) and the Ropeway. I was lucky to meet 6 other backpackers at my hostel and we ended up pooling the cab at INR 200 per person, with INR 1400 being on the expensive side, but you could bargain.
• Get lunch, buy some tea at Golden Tips, pack your bags and hop on a shared-cab back to Siliguri. It took us about 4hrs to reach Siliguri, with an hour to spare before my train.
• If you ve still got time on your hands, then check out the Peace Pagoda and the Darjeeling Himalayan Railway (Toy Train). At INR 1500, I found the latter to be too expensive and skipped it.

---

Tips and hacks

• Download offline maps, especially when you re exploring Northern Sikkim.
• Food and booze are the cheapest in Gangtok. Stash up before heading to other regions.
• Keep your Aadhar/Passport handy since you need permits to travel to North & East Sikkim.
• In rural areas and some cafes, you may get to try Rhododendron Wine, made from Rhododendron arboreum a.k.a Gurans. Its production is a little hush-hush since the flower is considered holy and is also the National Flower of Nepal.
• If you don t want to invest in a new jacket, boots or a pair of gloves, you can always rent them at nominal rates from your hotel or little stores around tourist sites.
• Check the weather of a region before heading there. Low visibility and precipitation can quite literally dampen your experience.
• Keep your itinerary flexible to accommodate for rest and impromptu plans.
• Shops and restaurants close by 8pm in Sikkim and Darjeeling. Plan for the same.

Carry

• a couple of extra pairs of socks (woollen, if possible)
• a pair of slippers to wear indoors
• a reusable water bottle
• an umbrella
• a power bank
• a couple of tablets of Diamox. Helps deal with altitude sickness
• extra clothes and wet bags since you may not get a chance to wash/dry your clothes
• a few passport size photographs

Shared-cab hacks

• Intercity rides can be exhausting. If you can afford it, pay for an additional seat.
• Call shotgun on the drives beyond Lachen and Lachung. The views are breathtaking.
• Return cabs tend to be cheaper (WB cabs travelling from SK and vice-versa)

Cost

• My median daily expenditure (back when I went to Sikkim in early March 2021) was INR 1350.
• This includes stay (bunk bed), food, wine and transit (shared cabs)
• In my defence, I splurged on food, wine and extra seats in shared cabs, but if you re on a budget, you could easily get by on INR 1 - 1.2k per day.
• For a 9-day trip, I ended up shelling out nearly INR 15k, including 2AC trains to & from Kolkata
• Note : Summer (March to May) and Autumn (October to December) are peak seasons, and thereby more expensive to travel around.

---

Souvenirs and things you should buy

Buddhist souvenirs :

• Colourful Prayer Flags (great for tying on bikes or behind car windshields)
• Miniature Prayer/Mani Wheels
• Lucky Charms, Pendants and Key Chains
• Cham Dance masks and robes
• Singing Bowls
• Common symbols: Om mani padme hum, Ashtamangala, Zodiac signs

Handicrafts & Handlooms

• Tibetan Yak Wool shawls, scarfs and carpets
• Sikkimese Ceramic cups
• Thangka Paintings

Edibles

• Darjeeling Tea (usually brewed and not boiled)
• Wine (Arucha Peach & Rhododendron)
• Dalle Khursani (Chilli) Paste and Pickle

Header Icon made by Freepik from www.flaticon.com is licensed by CC 3.0 BY

One of my goals for Consfigurator is to make it capable of installing Debian to my laptop, so that I can stop booting to GRML and manually partitioning and debootstrapping a basic system, only to then turn to configuration management to set everything else up. My configuration management should be able to handle the partitioning and debootstrapping, too. The first stage was to make Consfigurator capable of debootstrapping a basic system, chrooting into it, and applying other arbitrary configuration, such as installing packages. That s been in place for some weeks now. It s sophisticated enough to avoid starting up newly installed services, but I still need to add some bind mounting. Another significant piece is teaching Consfigurator how to partition block devices. That s quite tricky to do in a sufficiently general way I want to cleanly support various combinations of LUKS, LVM and regular partitions, including populating /etc/crypttab and /etc/fstab. I have some ideas about how to do it, but it ll probably take a few tries to get the abstractions right. Let s imagine that code is all in place, such that Consfigurator can be pointed at a block device and it will install a bootable Debian system to it. Then to install Debian to my laptop I d just need to take my laptop s disk drive out and plug it into another system, and run Consfigurator on that system, as root, pointed at the block device representing my laptop s disk drive. For virtual machines, it would be easy to write code which loop-mounts an empty disk image, and then Consfigurator could be pointed at the loop-mounted block device, thereby making the disk image file bootable. This is adequate for virtual machines, or small single-board computers with tiny storage devices (not that I actually use any of those, but I want Consfigurator to be able to make disk images for them!). But it s not much good for my laptop. I casually referred to taking out my laptop s disk drive and connecting it to another computer, but this would void my laptop s warranty. And Consfigurator would not be able to update my laptop s NVRAM, as is needed on UEFI systems. What s wanted here is a live system which can run Consfigurator directly on the laptop, pointed at the block device representing its physical disk drive. Ideally this live system comes with a chroot with the root filesystem for the new Debian install already built, so that network access is not required, and all Consfigurator has to do is partition the drive and copy in the contents of the chroot. The live system could be set up to automatically start doing that upon boot, but another option is to just make Consfigurator itself available to be used interactively. The user boots the live system, starts up Emacs, starts up Lisp, and executes a Consfigurator deployment, supplying the block device representing the laptop s disk drive as an argument to the deployment. Consfigurator goes off and partitions that drive, copies in the contents of the chroot, and executes grub-install to make the laptop bootable. This is also much easier to debug than a live system which tries to start partitioning upon boot. It would look something like this:

    ;; melete.silentflame.com is a Consfigurator host object representing the
    ;; laptop, including information about the partitions it should have
    (deploy-these :local ...
      (chroot:partitioned-and-installed
        melete.silentflame.com "/srv/chroot/melete" "/dev/nvme0n1"))

Now, building live systems is a fair bit more involved than installing Debian to a disk drive and making it bootable, it turns out. While I want Consfigurator to be able to completely replace the Debian Installer, I decided that it is not worth trying to reimplement the relevant parts of the Debian Live tool suite, because I do not need to make arbitrary customisations to any live systems. I just need to have some packages installed and some files in place. Nevertheless, it is worth teaching Consfigurator how to invoke Debian Live, so that the customisation of the chroot which isn t just a matter of passing options to lb_config(1) can be done with Consfigurator. This is what I ve ended up with in Consfigurator s source code:

(defpropspec image-built :lisp (config dir properties)
  "Build an image under DIR using live-build(7), where the resulting live
system has PROPERTIES, which should contain, at a minimum, a property from
CONSFIGURATOR.PROPERTY.OS setting the Debian suite and architecture.  CONFIG
is a list of arguments to pass to lb_config(1), not including the '-a' and
'-d' options, which Consfigurator will supply based on PROPERTIES.
This property runs the lb_config(1), lb_bootstrap(1), lb_chroot(1) and
lb_binary(1) commands to build or rebuild the image.  Rebuilding occurs only
when changes to CONFIG or PROPERTIES mean that the image is potentially
out-of-date; e.g. if you just add some new items to PROPERTIES then in most
cases only lb_chroot(1) and lb_binary(1) will be re-run.
Note that lb_chroot(1) and lb_binary(1) both run after applying PROPERTIES,
and might undo some of their effects.  For example, to configure
/etc/apt/sources.list, you will need to use CONFIG not PROPERTIES."
  (:desc (declare (ignore config properties))
         #?"Debian Live image built in $ dir ")
  (let* (...)
    ;; ...
     (eseqprops
      ;; ...
      (on-change
          (eseqprops
           (on-change
               (file:has-content ,auto/config ,(auto/config config) :mode #o755)
             (file:does-not-exist ,@clean)
             (%lbconfig ,dir)
             (%lbbootstrap t ,dir))
           (%lbbootstrap nil ,dir)
           (deploys ((:chroot :into ,chroot)) ,host))
        (%lbchroot ,dir)
        (%lbbinary ,dir)))))

Here, %lbconfig is a property running lb_config(1), %lbbootstrap one which runs lb_bootstrap(1), etc. Those properties all just change directory to the right place and run the command, essentially, with a little extra code to handle failed debootstraps and the like. The ON-CHANGE and ESEQPROPS combinators work together to sequence the interaction of the Debian Live suite and Consfigurator.

• In the innermost ON-CHANGE expression: create the file auto/config and populate it with the call to lb_config(1) that we need to make, as described in the Debian Live manual, chapter 6.
  • If doing so resulted in a change to the auto/config file e.g. the user added some more options ensure that lb_config(1) and lb_bootstrap(1) both get rerun.
• Now in the inner ESEQPROPS expression, use DEPLOYS to configure the chroot, essentially by forking into the chroot and recursively reinvoking Consfigurator.
• Finally, if any of the above resulted in a change being made, call lb_chroot(1) and lb_binary(1).

This way, we only rebuild the chroot if the configuration changed, and we only rebuild the image if the chroot changed. Now over in my personal consfig:

(try-register-data-source
 :git-snapshot :name "consfig" :repo #P"src/cl/consfig/" ...)
(defproplist hybrid-live-iso-built :lisp ()
  "Build a Debian Live system in /srv/live/spw.
Typically this property is not applied in a DEFHOST form, but rather run as
needed at the REPL.  The reason for this is that otherwise the whole image will
get rebuilt each time a commit is made to my dotfiles repo or to my consfig."
  (:desc "Sean's Debian Live system image built")
  (live-build:image-built.
      '("--archive-areas" "main contrib non-free" ...)
      "/srv/live/spw"
    (os:debian-stable "buster" :amd64)
    (basic-props)
    (apt:installed "whatever" "you" "want")
    (git:snapshot-extracted "/etc/skel/src" "dotfiles")
    (file:is-copy-of "/etc/skel/.bashrc" "/etc/skel/src/dotfiles/.bashrc")
    (git:snapshot-extracted "/root/src/cl" "consfig")))

The first argument to LIVE-BUILD:IMAGE-BUILT. is additional arguments to lb_config(1). The third argument onwards are the properties for the live system. The cool thing is GIT:SNAPSHOT-EXTRACTED the calls to this ensure that a copy of my Emacs configuration and my consfig end up in the live image, ready to be used interactively to install Debian, as described above. I ll need to add something like (chroot:host-chroot-bootstrapped melete.silentflame.com "/srv/chroot/melete") too. As with everything Consfigurator-related, Joey Hess s Propellor is the giant upon whose shoulders I m standing.

Last weekend Debian Quebec held a Bug Squashing Party to try to fix some bugs in the upcoming Debian Bullseye. I wasn't convinced at first, but Tassia's contagious energy and willingness to help organise the event eventually won me over. And shockers! it was really fun. We fixed a couple of RC bugs, held lightning talks and had a virtual pizza party! My lightning talk on autopkgtests was well received and a few people decided to migrate to sbuild and enable autopkgtests by default. Sergio's talk on debuginfod was incredibly interesting. I'm not a C programmer and the live demo made me understand how this service can help making debugging C easier. Jerome's talk on using Yubikeys to unlock LUKS encrypted drives was also very good! It also served as a reminder that Yubico's product are much more featureful and convenient to use than other Open Hardware/ Free Software hardware tokens. Hopefully that will change as enterprises like Nitrokey and Solokey mature. This was my third BSP, crazy how time flies... With the Bullseye release closing in, you should try to join or organise one!

I was going OK with Thunderbird and enigmail(though it have many problems). Normally I go through changelogs before updating packages and rarely do a complete upgrage of my machine. Couple of days ago I did a complete upgrade of system which updated my Thunderbird to latest version and throwing of enigmail plugin for using their native openPGP support. There is a blog from Mozilla which I should ve read earlier. Thunderbird s builtin openPGP functionality is still in experimental, atleast not ready for my workflow. I could ve downgrade to version 68. But I chose to move to my secondary MUA, mutt. I was using mutt for emails and newsletters that I check twice in a year a so. So I started configuring mutt to handle my big mailboxes. It took three evenings to configure mutt to my workflow. Though the basic setup can be done in less than an hour it is the small nitpicks consumed much of my time. Currently I have isync to pull and keep mails offline. Mutt to read, msmtp to send, abook as the email address book and urlview to see the links in mail. I am still learning notmuch and virtual mailbox ways to filter. There are ton of articles out there to configure mutt and all related things to it. But I find certain configs very hard to get. So I will write down those.

• As a long Thunderbird user, I still want my mailbox index to look in a certain way. I used;

   set date_format="%d/%m/%y %I:%M %p"
   set index_format="%3C   %Z %?X?@& ? %-22.17L %-5.50s %> %-22.20D"
  

  This gives following order - serial number, various flags (if there is an attachment, it will shows @ ), sender, subject and to extreme right there will be date and time (12h local) of mail
• If use nano to write mails you can use

  set editor="nano --syntax=email -r 70 -b"
  

  to get 70 char length and mail related syntax highlighting
• mutt has a way to make new mail notification. The new_mail_command can be used to execute a custom script upon new mail, such as running notify-send. There are many standalone mail notifier such as mailnag, mail notification etc. It all just felt bulky for me. So I ended up making these.

  #!/bin/sh
  accounts="$(awk '/^Channel/  print $2 ' "$MBSYNCRC")"
  for account in $accounts; do
       acc="$(echo "$account"   sed "s/.*\///")"
       new=$(find "$MAILBOX/$acc/Inbox/new/" -type f -newer "$MUTT/.mailsynclastrun" 2> /dev/null)
       newcount=$(echo "$new"   sed '/^\s*$/d'   wc -l)
       if [ "$newcount" -gt "0" ]; then
               for file in $new; do
               # Extract subject and sender from mail.
               from=$(awk '/^From: / && ++n ==1,/^\<.*\>:/' "$file"   perl -CS -MEncode -ne 'print decode("MIME-Header", $_)'   awk '  $1=""; if (NF>=3)$NF=""; print $0  '   sed 's/^[[:blank:]]*[\"'\''\<]*//;s/[\"'\''\>]*[[:blank:]]*$//')
               subject=$(awk '/^Subject: / && ++n == 1,/^\<.*\>: / && ++i == 2' "$file"   head -n 1   perl -CS -MEncode -ne 'print decode("MIME-Header", $_)'   sed 's/^Subject: //'   sed 's/^ [[:blank:]]*[\"'\''\<]*//;s/[\"'\''\>]*[[:blank:]]*$//'   tr -d '\n')
               displays="$(pgrep -a Xorg   grep -wo "[0-9]*:[0-9]\+")"
                       for x in $displays; do
                               export DISPLAY=$x
                               notify-send -i $MUTT/mutt.png -t 5000 "$account received new message:" "$from: <i>$subject</i>"
                       done
               done
       fi
  done
  touch "$MUTT/.mailsynclastrun" 
  

  And hooked to mail_new_command. This code snippet is from lukesmith s mutt-wizard, I barely modified to meet my need. Currently it only look in to Inbox . I need to modify to check other mailbox folders in future.

So far, everything going okay.

Cons

• some times mbsync throws EOF and secret key not found error.
• searching is still a pain in mutt
• nano s spell checker also check things which I am replying to.

More to come Well for now I moved mail from part of the Thunderbird. But Thunderbird was more than a MUA to me. It was my RSS reader, calendar and to-do list manager. I will write more about those once I make a complete transition.

Welcome to the September 2020 report from the Reproducible Builds project. In our monthly reports, we attempt to summarise the things that we have been up to over the past month, but if you are interested in contributing to the project, please visit our main website. This month, the Reproducible Builds project was pleased to announce a donation from Amateur Radio Digital Communications (ARDC) in support of its goals. ARDC s contribution will propel the Reproducible Builds project s efforts in ensuring the future health, security and sustainability of our increasingly digital society. Amateur Radio Digital Communications (ARDC) is a non-profit which was formed to further research and experimentation with digital communications using radio, with a goal of advancing the state of the art of amateur radio and to educate radio operators in these techniques. You can view the full announcement as well as more information about ARDC on their website.
In August s report, we announced that Jennifer Helsby (redshiftzero) launched a new reproduciblewheels.com website to address the lack of reproducibility of Python wheels . This month, Kushal Das posted a brief follow-up to provide an update on reproducible sources as well. The Threema privacy and security-oriented messaging application announced that within the next months , their apps will become fully open source, supporting reproducible builds :

This is to say that anyone will be able to independently review Threema s security and verify that the published source code corresponds to the downloaded app.

You can view the full announcement on Threema s website.

Events Sadly, due to the unprecedented events in 2020, there will be no in-person Reproducible Builds event this year. However, the Reproducible Builds project intends to resume meeting regularly on IRC, starting on Monday, October 12th at 18:00 UTC (full announcement). The cadence of these meetings will probably be every two weeks, although this will be discussed and decided on at the first meeting. (An editable agenda is available.) On 18th September, Bernhard M. Wiedemann gave a presentation in German titled Wie reproducible builds Software sicherer machen ( How reproducible builds make software more secure ) at the Internet Security Digital Days 2020 conference. (View video.) On Saturday 10th October, Morten Linderud will give a talk at Arch Conf Online 2020 on The State of Reproducible Builds in the Arch Linux distribution:

The previous year has seen great progress in Arch Linux to get reproducible builds in the hands of the users and developers. In this talk we will explore the current tooling that allows users to reproduce packages, the rebuilder software that has been written to check packages and the current issues in this space.

During the Reproducible Builds summit in Marrakesh, GNU Guix, NixOS and Debian were able to produce a bit-for-bit identical binary when building GNU Mes, despite using three different major versions of GCC. Since the summit, additional work resulted in a bit-for-bit identical Mes binary using tcc and this month, a fuller update was posted by the individuals involved.

Development work In openSUSE, Bernhard M. Wiedemann published his monthly Reproducible Builds status update.

Debian Chris Lamb uploaded a number of Debian packages to address reproducibility issues that he had previously provided patches for, including cfingerd (#831021), grap (#870573), splint (#924003) & schroot (#902804) Last month, an issue was identified where a large number of Debian .buildinfo build certificates had been tainted on the official Debian build servers, as these environments had files underneath the /usr/local/sbin directory to prevent the execution of system services during package builds. However, this month, Aurelien Jarno and Wouter Verhelst fixed this issue in varying ways, resulting in a special policy-rcd-declarative-deny-all package. Building on Chris Lamb s previous work on reproducible builds for Debian .ISO images, Roland Clobus announced his work in progress on making the Debian Live images reproducible. [ ] Lucas Nussbaum performed an archive-wide rebuild of packages to test enabling the reproducible=+fixfilepath Debian build flag by default. Enabling the fixfilepath feature will likely fix reproducibility issues in an estimated 500-700 packages. The test revealed only 33 packages (out of 30,000 in the archive) that fail to build with fixfilepath. Many of those will be fixed when the default LLVM/Clang version is upgraded. 79 reviews of Debian packages were added, 23 were updated and 17 were removed this month adding to our knowledge about identified issues. Chris Lamb added and categorised a number of new issue types, including packages that captures their build path via quicktest.h and absolute build directories in documentation generated by Doxygen , etc. Lastly, Lukas Puehringer s uploaded a new version of the in-toto to Debian which was sponsored by Holger Levsen. [ ]

diffoscope diffoscope is our in-depth and content-aware diff utility that can not only locate and diagnose reproducibility issues, it provides human-readable diffs of all kinds too. In September, Chris Lamb made the following changes to diffoscope, including preparing and uploading versions 159 and 160 to Debian:

• New features:
  • Show ordering differences only in strings(1) output by applying the ordering check to all differences across the codebase. [ ]
• Bug fixes:
  • Mark some PGP tests that they require pgpdump, and check that the associated binary is actually installed before attempting to run it. (#969753)
  • Don t raise exceptions when cleaning up after guestfs cleanup failure. [ ]
  • Ensure we check FALLBACK_FILE_EXTENSION_SUFFIX, otherwise we run pgpdump against all files that are recognised by file(1) as data. [ ]
• Codebase improvements:
  • Add some documentation for the EXTERNAL_TOOLS dictionary. [ ]
  • Abstract out a variable we use a couple of times. [ ]
• diffoscope.org website improvements:
  • Make the (long) demonstration GIF less prominent on the page. [ ]

In addition, Paul Spooren added support for automatically deploying Docker images. [ ]

Website and documentation This month, a number of updates to the main Reproducible Builds website and related documentation. Chris Lamb made the following changes:

• Update a few titles and the ordering of some top-level navigation elements. [ ]
• Drafted, published and publicised August s monthly report.
• Improve the documentation on how to signup to Salsa. [ ]
• Add some more links to academic papers. [ ]
• Also include the general news in our RSS feed [ ] and drop including weekly reports from the RSS feed (they are never shown now that we have over 10 items) [ ].
• Update ordering and location of various news and links to tarballs, etc. [ ][ ][ ]
• Kept isdebianreproducibleyet.com up to date. [ ]
• Worked with Amateur Radio Digital Communications in order to announce their generous sponsorship of the Reproducible Builds project.

In addition, Holger Levsen re-added the documentation link to the top-level navigation [ ] and documented that the jekyll-polyglot package is required [ ]. Lastly, diffoscope.org and reproducible-builds.org were transferred to Software Freedom Conservancy. Many thanks to Brett Smith from Conservancy, J r my Bobbio (lunar) and Holger Levsen for their help with transferring and to Mattia Rizzolo for initiating this.

Upstream patches The Reproducible Builds project detects, dissects and attempts to fix as many currently-unreproducible packages as possible. We endeavour to send all of our patches upstream where appropriate. This month, we wrote a large number of these patches, including:

• Bernhard M. Wiedemann:
  • cfn-python-lint (build failure)
  • clutter (avoid a random ID in HTML from xsltproc)
  • kubernetes (1-bit order in manual page)
  • libint (merged, filesystem order)
  • libmysofa (disable -fprofile-arcs and code coverage)
  • libnet (merged, date)
  • libqb (date / copyright)
  • libsemigroups (CPU detection)
  • nauty (CPU type detection)
• Chris Lamb:
  • #970024 filed against cif2cell.
  • #970278 filed against smartlist.
  • #970383 filed against evince.
  • #970498 filed against libiio.
  • #970851 filed against check-pgbackrest.
  • #970908 filed against smartdns.
  • #971420 filed against jhbuild.
• kpcyrd:
  • git2-rs (sort return ordering of readdir(3))
• Vagrant Cascadian:
  • #970874 filed against nix.
  • #970888 & #970890 filed against fai.
  • #970893 filed against debdelta.
  • #971400 & #971402 filed against vboot-utils.
  • #971408 filed against simde.

Bernhard M. Wiedemann also reported issues in git2-rs, pyftpdlib, python-nbclient, python-pyzmq & python-sidpy.

Testing framework The Reproducible Builds project operates a Jenkins-based testing framework to power tests.reproducible-builds.org. This month, Holger Levsen made the following changes:

• Debian:
  • Shorten the subject of nodes have gone offline notification emails. [ ]
  • Also track bugs that have been usertagged with usrmerge. [ ]
  • Drop abort-related codepaths as that functionality has been removed from Jenkins. [ ]
  • Update the frequency we update base images and status pages. [ ][ ][ ][ ]
• Status summary view page:
  • Add support for monitoring systemctl status [ ] and the number of diffoscope processes [ ].
  • Show the total number of nodes [ ] and colourise critical disk space situations [ ].
  • Improve the visuals with respect to vertical space. [ ][ ]
• Debian rebuilder prototype:
  • Resume building random packages again [ ] and update the frequency that packages are rebuilt. [ ][ ]
  • Use --no-respect-build-path parameter until sbuild 0.81 is available. [ ]
  • Treat the inability to locate some packages as a debrebuild problem, and not as a issue with the rebuilder itself. [ ]
• Arch Linux:
  • Update various components to be compatible with Arch Linux s move to the xz compression format. [ ][ ][ ]
  • Allow scheduling of old packages to catch up on the backlog. [ ][ ][ ]
  • Improve formatting on the summary page. [ ][ ]
  • Update HTML pages once every hour, not every 30 minutes. [ ]
  • Use the Ubuntu (!) GPG keyserver to validate packages. [ ]
• System health checks:
  • Highlight important bad conditions in colour. [ ][ ]
  • Add support for detecting more problems, including Jenkins shutdown issues [ ], failure to upgrade Arch Linux packages [ ], kernels with wrong permissions [ ], etc.
• Misc:
  • Delete old schroot sessions after 2 days, not 3. [ ]
  • Use sudo to cleanup diffoscope schroot sessions. [ ]

In addition, stefan0xC fixed a query for unknown results in the handling of Arch Linux packages [ ] and Mattia Rizzolo updated the template that notifies maintainers by email of their newly-unreproducible packages to ensure that it did not get caught in junk/spam folders [ ]. Finally, build node maintenance was performed by Holger Levsen [ ][ ][ ][ ], Mattia Rizzolo [ ][ ] and Vagrant Cascadian [ ][ ][ ].
If you are interested in contributing to the Reproducible Builds project, please visit our Contribute page on our website. However, you can get in touch with us via:

• IRC: #reproducible-builds on irc.oftc.net.
• Twitter: @ReproBuilds
• Mastodon: @reproducible_builds@fosstodon.org
• Mailing list: rb-general@lists.reproducible-builds.org

Welcome to the August 2020 report from the Reproducible Builds project. In our monthly reports, we summarise the things that we have been up to over the past month. The motivation behind the Reproducible Builds effort is to ensure no flaws have been introduced from the original free software source code to the pre-compiled binaries we install on our systems. If you re interested in contributing to the project, please visit our main website.

---

This month, Jennifer Helsby launched a new reproduciblewheels.com website to address the lack of reproducibility of Python wheels. To quote Jennifer s accompanying explanatory blog post:

One hiccup we ve encountered in SecureDrop development is that not all Python wheels can be built reproducibly. We ship multiple (Python) projects in Debian packages, with Python dependencies included in those packages as wheels. In order for our Debian packages to be reproducible, we need that wheel build process to also be reproducible

Parallel to this, transparencylog.com was also launched, a service that verifies the contents of URLs against a publicly recorded cryptographic log. It keeps an append-only log of the cryptographic digests of all URLs it has seen. (GitHub repo) On 18th September, Bernhard M. Wiedemann will give a presentation in German, titled Wie reproducible builds Software sicherer machen ( How reproducible builds make software more secure ) at the Internet Security Digital Days 2020 conference.

Reproducible builds at DebConf20 There were a number of talks at the recent online-only DebConf20 conference on the topic of reproducible builds. Holger gave a talk titled Reproducing Bullseye in practice , focusing on independently verifying that the binaries distributed from ftp.debian.org are made from their claimed sources. It also served as a general update on the status of reproducible builds within Debian. The video (145 MB) and slides are available. There were also a number of other talks that involved Reproducible Builds too. For example, the Malayalam language mini-conference had a talk titled , ? ( I want to join Debian, what should I do? ) presented by Praveen Arimbrathodiyil, the Clojure Packaging Team BoF session led by Elana Hashman, as well as Where is Salsa CI right now? that was on the topic of Salsa, the collaborative development server that Debian uses to provide the necessary tools for package maintainers, packaging teams and so on. Jonathan Bustillos (Jathan) also gave a talk in Spanish titled Un camino verificable desde el origen hasta el binario ( A verifiable path from source to binary ). (Video, 88MB)

Development work After many years of development work, the compiler for the Rust programming language now generates reproducible binary code. This generated some general discussion on Reddit on the topic of reproducibility in general. Paul Spooren posted a request for comments to OpenWrt s openwrt-devel mailing list asking for clarification on when to raise the PKG_RELEASE identifier of a package. This is needed in order to successfully perform rebuilds in a reproducible builds context. In openSUSE, Bernhard M. Wiedemann published his monthly Reproducible Builds status update. Chris Lamb provided some comments and pointers on an upstream issue regarding the reproducibility of a Snap / SquashFS archive file. [ ]

Debian Holger Levsen identified that a large number of Debian .buildinfo build certificates have been tainted on the official Debian build servers, as these environments have files underneath the /usr/local/sbin directory [ ]. He also filed against bug for debrebuild after spotting that it can fail to download packages from snapshot.debian.org [ ]. This month, several issues were uncovered (or assisted) due to the efforts of reproducible builds. For instance, Debian bug #968710 was filed by Simon McVittie, which describes a problem with detached debug symbol files (required to generate a traceback) that is unlikely to have been discovered without reproducible builds. In addition, Jelmer Vernooij called attention that the new Debian Janitor tool is using the property of reproducibility (as well as diffoscope when applying archive-wide changes to Debian:

New merge proposals also include a link to the diffoscope diff between a vanilla build and the build with changes. Unfortunately these can be a bit noisy for packages that are not reproducible yet, due to the difference in build environment between the two builds. [ ]

56 reviews of Debian packages were added, 38 were updated and 24 were removed this month adding to our knowledge about identified issues. Specifically, Chris Lamb added and categorised the nondeterministic_version_generated_by_python_param and the lessc_nondeterministic_keys toolchain issues. [ ][ ] Holger Levsen sponsored Lukas Puehringer s upload of the python-securesystemslib pacage, which is a dependency of in-toto, a framework to secure the integrity of software supply chains. [ ] Lastly, Chris Lamb further refined his merge request against the debian-installer component to allow all arguments from sources.list files (such as [check-valid-until=no]) in order that we can test the reproducibility of the installer images on the Reproducible Builds own testing infrastructure and sent a ping to the team that maintains that code.

Upstream patches The Reproducible Builds project detects, dissects and attempts to fix as many currently-unreproducible packages as possible. We endeavour to send all of our patches upstream where appropriate. This month, we wrote a large number of these patches, including:

• Bernhard M. Wiedemann:
  • asymptote (shell/Perl date)
  • getfem (embeds datetime and user, submitted via email)
  • getdp (hostname and user)
  • getdp (user)
  • guix (disable parallelism)
  • httpcomponents-client (Java documentation generator readdir order)
  • kuberlr (date)
  • lal (date and time issue, submitted via email)
  • libmesh (host)
  • OBS (discuss how to track old build prjconf metadata in buildinfo)
  • openblas (disable CPU detection)
  • openfoam-selector (date)
  • perl (toolchain, date)
  • python-blosc (CPU detection)
  • python-eventlet (fails to build far in the future)
  • rna-star (date and hostname)
  • trilinos (date)
  • xz/b4 (workaround CPU count influencing output, reported upstream)
• Benjamin Hof:
  • flit
• Chris Lamb:
  • #966657 filed against json-c (forwarded upstream).
  • #967238 filed against nmh.
  • #968045 filed against golang-gonum-v1-plot.
  • #968183 filed against chirp.
  • #968185 filed against pixelmed-codec.
  • #968187 filed against debhelper.
  • #968189 filed against muroar.
  • #968278 filed against serd.
  • #968344 filed against pencil2d.
  • #968557 filed against tpot.
  • #968700 filed against evolution.
  • #969320 filed against aflplusplus.
• Herv Boutemy:
  • plexus-archiver (timezone/DST issue)
• Vagrant Cascadian:
  • #968627 filed against libjpeg-turbo.
  • #968641 filed against jack-audio-connection-kit.
  • #968652 filed against glusterfs.

diffoscope diffoscope is our in-depth and content-aware diff utility that can not only locate and diagnose reproducibility issues, it provides human-readable diffs of all kinds. In August, Chris Lamb made the following changes to diffoscope, including preparing and uploading versions 155, 156, 157 and 158 to Debian:

• New features:
  • Support extracting data of PGP signed data. (#214)
  • Try files named .pgp against pgpdump(1) to determine whether they are Pretty Good Privacy (PGP) files. (#211)
  • Support multiple options for all file extension matching. [ ]
• Bug fixes:
  • Don t raise an exception when we encounter XML files with <!ENTITY> declarations inside the Document Type Definition (DTD), or when a DTD or entity references an external resource. (#212)
  • pgpdump(1) can successfully parse some binary files, so check that the parsed output contains something sensible before accepting it. [ ]
  • Temporarily drop gnumeric from the Debian build-dependencies as it has been removed from the testing distribution. (#968742)
  • Correctly use fallback_recognises to prevent matching .xsb binary XML files.
  • Correct identify signed PGP files as file(1) returns data . (#211)
• Logging improvements:
  • Emit a message when ppudump version does not match our file header. [ ]
  • Don t use Python s repr(object) output in Calling external command messages. [ ]
  • Include the filename in the not identified by any comparator message. [ ]
• Codebase improvements:
  • Bump Python requirement from 3.6 to 3.7. Most distributions are either shipping with Python 3.5 or 3.7, so supporting 3.6 is not only somewhat unnecessary but also cumbersome to test locally. [ ]
  • Drop some unused imports [ ], drop an unnecessary dictionary comprehensions [ ] and some unnecessary control flow [ ].
  • Correct typo of output in a comment. [ ]
• Release process:
  • Move generation of debian/tests/control to an external script. [ ]
  • Add some URLs for the site that will appear on PyPI.org. [ ]
  • Update author and author email in setup.py for PyPI.org and similar. [ ]
• Testsuite improvements:
  • Update PPU tests for compatibility with Free Pascal versions 3.2.0 or greater. (#968124)
  • Mark that our identification test for .ppu files requires ppudump version 3.2.0 or higher. [ ]
  • Add an assert_diff helper that loads and compares a fixture output. [ ][ ][ ][ ]
• Misc:
  • Duplicate docker instructions in the Get diffoscope section of the diffoscope website. [ ]

In addition, Mattia Rizzolo documented in setup.py that diffoscope works with Python version 3.8 [ ] and Frazer Clews applied some Pylint suggestions [ ] and removed some deprecated methods [ ].

Website This month, Chris Lamb updated the main Reproducible Builds website and documentation to:

• Clarify & fix a few entries on the who page [ ][ ] and ensure that images do not get to large on some viewports [ ].
• Clarify use of a pronoun re. Conservancy. [ ]
• Use View all our monthly reports over View all monthly reports . [ ]
• Move a is a suffix out of the link target on the SOURCE_DATE_EPOCH age. [ ]

In addition, Javier Jard n added the freedesktop-sdk project [ ] and Kushal Das added SecureDrop project [ ] to our projects page. Lastly, Michael P hn added internationalisation and translation support with help from Hans-Christoph Steiner [ ].

Testing framework The Reproducible Builds project operate a Jenkins-based testing framework to power tests.reproducible-builds.org. This month, Holger Levsen made the following changes:

• System health checks:
  • Improve explanation how the status and scores are calculated. [ ][ ]
  • Update and condense view of detected issues. [ ][ ]
  • Query the canonical configuration file to determine whether a job is disabled instead of duplicating/hardcoding this. [ ]
  • Detect several problems when updating the status of reporting-oriented metapackage sets. [ ]
  • Detect when diffoscope is not installable [ ] and failures in DNS resolution [ ].
• Debian:
  • Update the URL to the Debian security team bug tracker s Git repository. [ ]
  • Reschedule the unstable and bullseye distributions often for the arm64 architecture. [ ]
  • Schedule buster less often for armhf. [ ][ ][ ]
  • Force the build of certain packages in the work-in-progress package rebuilder. [ ][ ]
  • Only update the stretch and buster base build images when necessary. [ ]
• Other distributions:
  • For F-Droid, trigger jobs by commits, not by a timer. [ ]
  • Disable the Archlinux HTML page generation job as it has never worked. [ ]
  • Disable the alternative OpenWrt rebuilder jobs. [ ]
• Misc;
  • Improve monitoring, such as number of mounts, disk, memory, etc.. [ ][ ][ ][ ]
  • Install the ruby-jekyll-polyglot package to needed for the recently-added internationalisation and translation support on the Reproducible Builds website. [ ]
  • Update link to report potential issues. [ ][ ]

Many other changes were made too, including:

• Chris Lamb:
  • Use <pre> HTML tags when dumping fixed-width debugging data in the self-serve package scheduler. [ ]
• Mattia Rizzolo:
  • For Alpine and ArchLinux, make the cleanup routines in the event of an error more robust. [ ]
  • Update the sudo configuration to permit Jenkins itself to unmount more directories. [ ]
  • Setup automatic renewal of our Let s Encrypt certificates for all domains served by us (including jenkins.debian.net, www.reproducible-builds.org, diffoscope.org, buildinfos.debian.net, etc.). [ ][ ][ ][ ][ ]
• Vagrant Cascadian:
  • Mark that the u-boot Universal Boot Loader should not build architecture independent packages on the arm64 architecture anymore. [ ]

Finally, build node maintenance was performed by Holger Levsen [ ], Mattia Rizzolo [ ][ ] and Vagrant Cascadian [ ][ ][ ][ ]

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Mailing list On our mailing list this month, Leo Wandersleb sent a message to the list after he was wondering how to expand his WalletScrutiny.com project (which aims to improve the security of Bitcoin wallets) from Android wallets to also monitor Linux wallets as well:

If you think you know how to spread the word about reproducibility in the context of Bitcoin wallets through WalletScrutiny, your contributions are highly welcome on this PR [ ]

Julien Lepiller posted to the list linking to a blog post by Tavis Ormandy titled You don t need reproducible builds. Morten Linderud (foxboron) responded with a clear rebuttal that Tavis was only considering the narrow use-case of proprietary vendors and closed-source software. He additionally noted that the criticism that reproducible builds cannot prevent against backdoors being deliberately introduced into the upstream source ( bugdoors ) are decidedly (and deliberately) outside the scope of reproducible builds to begin with. Chris Lamb included the Reproducible Builds mailing list in a wider discussion regarding a tentative proposal to include .buildinfo files in .deb packages, adding his remarks regarding requiring a custom tool in order to determine whether generated build artifacts are identical in a reproducible context. [ ] Jonathan Bustillos (Jathan) posted a quick email to the list requesting whether there was a list of To do tasks in Reproducible Builds. Lastly, Chris Lamb responded at length to a query regarding the status of reproducible builds for Debian ISO or installation images. He noted that most of the technical work has been performed but there are at least four issues until they can be generally advertised as such . He pointed that the privacy-oriented Tails operation system, which is based directly on Debian, has had reproducible builds for a number of years now. [ ]

---

If you are interested in contributing to the Reproducible Builds project, please visit our Contribute page on our website. However, you can get in touch with us via:

• IRC: #reproducible-builds on irc.oftc.net.
• Twitter: @ReproBuilds
• Mastodon: @reproducible_builds@fosstodon.org
• Mailing list: rb-general@lists.reproducible-builds.org

Introducing cryptsetup-suspend Today, we're introducing cryptsetup-suspend, whose job is to protect the content of your harddrives while the system is sleeping. TL;DR:

• You can lock your encrypted harddrives during suspend mode by installing cryptsetup-suspend
• For cryptsetup-suspend to work properly, at least Linux kernel 5.6 is required
• We hope that in a bright future, everything will be available out-of-the-box in Debian and it's derivatives

Before: After:

Table of contents

What does this mean and why should you care about it? If you don't use full-disk encryption, don't read any further. Instead, think about, what will happen if you lose your notebook on the train, a random person picks it up and browses through all your personal pictures, e-mails, and tax records. Then encrypt your system and come back. If you believe full-disk encryption is necessary, you might know that it only works when your machine is powered off. Once you turn on the machine and decrypt your harddrive, your encryption key stays in RAM and can potentially be extracted by malicious software or physical access. Even if these attacks are non-trivial, it's enough to worry about. If an attacker is able to extract your disk encryption keys from memory, they're able to read the content of your disk in return. Sadly, in 2020, we hardly power off our laptops anymore. The sleep mode, also known as "suspend mode", is just too convenient. Just close the lid to freeze the system state and lift it anytime later in order to continue. Well, convenience usually comes with a cost: during suspend mode, your system memory is kept powered, all your data - including your encryption keys - stays there, waiting to be extracted by a malicious person. Unfortunately, there are practical attacks to extract the data of your powered memory. Cryptsetup-suspend expands the protection of your full-disk encryption to all those times when your computer sleeps in suspend mode. Cryptsetup-suspend utilizes the suspend feature of LUKS volumes and integrates it with your Debian system. Encryption keys are evicted from memory before suspend mode and the volumes have to be re-opened after resuming - potentially prompting for the required passphrases. By now, we have a working prototype which we want to introduce today. We did quite some testing, both on virtualized and bare-metal Debian and Ubuntu systems, with and without graphical stack, so we dare to unseal and set free the project and ask you - the community - to test, review, criticize and give feedback. Here's a screencast of cryptsetup-suspend in action:

State of the implementation: where are we? If you're interested in the technical details, here's how cryptsetup-suspend works internally. It basically consists of three parts:

1. cryptsetup-suspend: A C program that takes a list of LUKS devices as arguments, suspends them via luksSuspend and suspends the system afterwards. Also, it tries to reserve some memory for decryption, which we'll explain below.
2. cryptsetup-suspend-wrapper: A shell wrapper script which works the following way:
   1. Extract the initramfs into a ramfs
   2. Run (systemd) pre-suspend scripts, stop udev, freeze almost all cgroups
   3. Chroot into the ramfs and run cryptsetup-suspend
   4. Resume initramfs devices inside chroot after resume
   5. Resume non-initramfs devices outside chroot
   6. Thaw groups, start udev, run (systemd) post-suspend scripts
   7. Unmount the ramfs
3. A systemd unit drop-in file overriding the Exec property of systemd-suspend.service so that it invokes the script cryptsetup-suspend-wrapper.

Reusing large parts of the existing cryptsetup-initramfs implementation has some positive side-effects: Out-of-the-box, we support all LUKS block device setups that have been supported by the Debian cryptsetup packages before. Freezing most processes/cgroups is necessary to prevent possible race-conditions and dead-locks after the system resumes. Processes will try to access data on the locked/suspended block devices eventually leading to buffer overflows and data loss.

Technical challenges and caveats

• Dead-locks at suspend: In order to prevent possible dead-locks between suspending the encrypted LUKS disks and suspending the system, we have to tell the Linux kernel to not sync() before going to sleep. A corresponding patch got accepted upstream in Linux 5.6. See section What about the kernel patch? below for details.
• Race conditions at resume: Likewise, there's a risk of race conditions between resuming the system and unlocking the encypted LUKS disks. We went with freezing as many processes as possible as a counter measurement. See last part of section State of the implementation: where are we? for details.
• Memory management: Memory management is definitely a challenge. Unlocking disks might require a lot of memory (if key derivation function is argon2i) and the swap device most likely is locked at that time. See section All that matters to me is the memories! below for details.
• systemd dependency: Our implementation depends on systemd. It uses a unit drop-in file for systemd-suspend.service for hooking into the system suspend process and depends on systemds cgroup management to freeze and thaw processes. If you're using a different init system, sorry, you're currently out of luck.

What about the kernel patch? The problem is simple: the Linux kernel suspend implementation enforces a final filesystem sync() before the system goes to sleep in order to prevent potential data loss. While that's sensible in most scenarios, it may result in dead-locks in our situation, since the block device that holds the filesystem is already suspended. The fssync() call will block forever as it waits for the block device to finish the sync() operation. So we need a way to conditionally disable this sync() call in the Linux kernel resume function. That's what our patch does, by introducing a run-time switch at /sys/power/sync_on_suspend, but it only got accepted into the Linux kernel recently and was first released with Linux kernel 5.6. Since release 4.3, the Linux kernel at least provides a build-time flag to disable the sync(): CONFIG_SUSPEND_SKIP_SYNC (that was called SUSPEND_SKIP_SYNC first and renamed to CONFIG_SUSPEND_SKIP_SYNC in kernel release 4.9). Enabling this flag at build-time protects you against the dead locks perfectly well. But while that works on an individual basis, it's a non-option for the distribution Linux kernel defaults. In most cases you still want the sync() to happen, except if you have user-space code that takes care of the sync() just before suspending your system - just like our cryptsetup-suspend implementation does. So in order to properly test cryptsetup-suspend, you're strongly advised to run Linux kernel 5.6 or newer. Fortunately, Linux 5.6 is available in buster-backports thanks to the Debian Kernel Team.

All that matters to me is the memories! One of the tricky parts is memory management. Since version 2, LUKS uses argon2i as default key derivation function. Argon2i is a memory-hard hash function and LUKS2 assigns the minimum of half of your systems memory or 1 GB to unlocking your device. While this is usually unproblematic during system boot - there's not much in the system memory anyway - it can become problematic when suspending. When cryptsetup tries to unlock a device and wants 1 GB of memory for this, but everything is already occupied by your browser and video player, there's only two options what to do:

1. Kill a process to free some memory
2. Move some of the data from memory to swap space

The first option is certainly not what you expect when suspending your system. The second option is impossible, because swap is located on your harddrive which we have locked before. Our current solution is to allocate the memory after freezing the other processes, but before locking the disks. At this time, the system can still move data to swap, but it won't be accessed anymore. We then release the memory just in time for cryptsetup to claim it again. The implementation of this is still subject to change.

What's missing: A proper user interface As mentioned before, we consider cryptsetup-suspend usable, but it certainly still has bugs and shortcomings. The most obvious one is lack of a proper user interface. Currently, we switch over to a tty command-line interface to prompt for passphrases when unlocking the LUKS devices. It certainly would be better to replace this with a graphical user interface later, probably by using plymouth or something alike. Unfortunately, it seems rather impossible to spawn a real graphical environment for the passphrase prompt. That would imply to load the full graphical stack into the ramfs, raising the required amount of memory significantly. Lack of memory is currently our biggest concern and source of trouble. We'd definitely appreciate to learn about your ideas how to improve the user experience here.

Let's get practical: how to use TL;DR: On Debian Bullseye (Testing), all you need to do is to install the cryptsetup-suspend package from experimental. It's not necessary to upgrade the other cryptsetup packages. On Debian Buster, cryptsetup packages from backports are required.

1. First, be sure that you're running Linux kernel 5.6 or newer. For Buster systems, it's available in buster-backports.
2. Second, if you're on Debian Buster, install the cryptsetup 2:2.3.3-2~bpo10+1 packages from buster-backports.
3. Third, install the cryptsetup-suspend package from experimental. Beware that cryptsetup-suspend depends on cryptsetup-initramfs (>= 2:2.3.3-1~). Either you need the cryptsetup packages from testing/unstable, or the backports from buster-backports.
4. Now that you have the cryptsetup-suspend package installed, everything should be in place: Just send your system to sleep. It should switch to a virtual text terminal before going to sleep, ask for a passphrase to unlock your encrypted disk(s) after resume and switch back to your former working environment (most likely your graphical desktop environment) afterwards.

Security considerations Suspending LUKS devices basically means to remove the corresponding encryption keys from system memory. This protects against all sort of attacks trying to read them from there, e.g. cold-boot attacks. But, cryptsetup-suspend only protects the encryption keys of your LUKS devices. Most likely there's more sensitive data in system memory, like all kinds of private keys (e.g. OpenPGP, OpenSSH) or documents with sensitive content. We hope that the community will help improve this situation by providing useful pre-/post-suspend scripts. A positive example is KeepassXC, which is able to lock itself when going to suspend mode.

Related and similar projects

• Systemd Homed: systemd recently got a new feature to manage home directories. It brings support for encrypting your home directory within a LUKS2 container and for suspending the LUKS2 container during system sleep. It all is limited to systemd home directories though and doesn't help with other LUKS devices.
• There's several earlier luks-suspend-* implementations. Unfortunately, neither of them deal with all the Technical challenges and caveats we discovered. Still we'd like to mention some of them:
• debian-luks-suspend
• go-luks-suspend
• arch-luks-suspend

Links

• Our Linux kernel patch: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c052bf82c6b00ca27aab0859addc4b3159dfd3a4
• The debian/experimental branch of our Debian cryptsetup packaging repository, containing cryptsetup-suspend related changes: https://salsa.debian.org/cryptsetup-team/cryptsetup/-/tree/debian/experimental
• cryptsetup-suspend manpage: https://salsa.debian.org/cryptsetup-team/cryptsetup/-/blob/debian/experimental/debian/doc/cryptsetup-suspend.xml

Feedback and Comments We'd be more than happy to learn about your thoughts on cryptsetup-suspend. For specific issues, don't hesitate to open a bugreport against cryptsetup-suspend. You can also reach us via mail - see the next section for contact addresses. Last but not least, comments below the blogpost work as well.

Authors

• Tim (tim at systemli.org)
• Jonas (jonas at freesources.org)

As we grow old, so do our computing machines. And just like we don t decommission ourselves, so should be the case of the machines. They should be semi-retired, delegating major tasks to newer machines while they can still serve some less demaning work: File Servers, UPNP Servers et cetera. It is common on a Debian installer based derivative, and otherwise too, to use block encryption on Linux. With machines from this decade, I think we ve always had CPU extension for encryption. So, as would be the usual case, all my laptops are block encrypted. But as they reach the phase of their life to retire and serving as a headless boss, it becomes cumbersome to keep feeding it a password and all the logistics involved to feed it. As such, I wanted to get rid of feeding it the password. Then, there s also the case of bad/faulty hardware, many of which mostly can temporarily fix their functionality when reset, which usually is to reboot the machine. I still recollect words of my Linux Guru - Dhiren Raj Bhandari - that many of the unexplainable errors can be resolved by just rebooting the machine. This was more than 20 years ago in the prime era of Microsoft Windows OS and the context back then was quite different, but yes, some bits of that saying still apply today. So I wanted my laptop, which had LUKS set up for 2 disks, to go password-less now. I stumbled across a slightly dated article where the author achieved similar results with keyscript. So the thing was doable. To my delight, Debian cryptsetup has the best setup and documentation in place to do it with just adding keyfiles and the nice integration in crypttab to ensure your keys propagate to initramfs The whole thing took me around 20-25 minutes, including drafting this post. From Retired Head and Password Prompt to Headless and Password-less. The beauty of Debian and FOSS

In case you are not yet familiar with why an initramfs (or initrd, or initial ramdisk) is typically used when starting Linux, let me quote the wikipedia definition: [ ] initrd is a scheme for loading a temporary root file system into memory, which may be used as part of the Linux startup process [ ] to make preparations before the real root file system can be mounted. Many Linux distributions do not compile all file system drivers into the kernel, but instead load them on-demand from an initramfs, which saves memory. Another common scenario, in which an initramfs is required, is full-disk encryption: the disk must be unlocked from userspace, but since userspace is encrypted, an initramfs is used.

Motivation Thus far, building a distri disk image was quite slow: This is on an AMD Ryzen 3900X 12-core processor (2019):

distri % time make cryptimage serial=1
80.29s user 13.56s system 186% cpu 50.419 total # 19s image, 31s initrd

Of these 50 seconds, dracut s initramfs generation accounts for 31 seconds (62%)! Initramfs generation time drops to 8.7 seconds once dracut no longer needs to use the single-threaded gzip(1) , but the multi-threaded replacement pigz(1) : This brings the total time to build a distri disk image down to:

distri % time make cryptimage serial=1
76.85s user 13.23s system 327% cpu 27.509 total # 19s image, 8.7s initrd

Clearly, when you use dracut on any modern computer, you should make pigz available. dracut should fail to compile unless one explicitly opts into the known-slower gzip. For more thoughts on optional dependencies, see Optional dependencies don t work . But why does it take 8.7 seconds still? Can we go faster? The answer is Yes! I recently built a distri-specific initramfs I m calling minitrd. I wrote both big parts from scratch:

1. the initramfs generator program (distri initrd)
2. a custom Go userland (cmd/minitrd), running as /init in the initramfs.

minitrd generates the initramfs image in 400ms, bringing the total time down to:

distri % time make cryptimage serial=1
50.09s user 8.80s system 314% cpu 18.739 total # 18s image, 400ms initrd

(The remaining time is spent in preparing the file system, then installing and configuring the distri system, i.e. preparing a disk image you can run on real hardware.) How can minitrd be 20 times faster than dracut? dracut is mainly written in shell, with a C helper program. It drives the generation process by spawning lots of external dependencies (e.g. ldd or the dracut-install helper program). I assume that the combination of using an interpreted language (shell) that spawns lots of processes and precludes a concurrent architecture is to blame for the poor performance. minitrd is written in Go, with speed as a goal. It leverages concurrency and uses no external dependencies; everything happens within a single process (but with enough threads to saturate modern hardware). Measuring early boot time using qemu, I measured the dracut-generated initramfs taking 588ms to display the full disk encryption passphrase prompt, whereas minitrd took only 195ms. The rest of this article dives deeper into how minitrd works.

What does an initramfs do? Ultimately, the job of an initramfs is to make the root file system available and continue booting the system from there. Depending on the system setup, this involves the following 5 steps:

1. Load kernel modules to access the block devices with the root file system Depending on the system, the block devices with the root file system might already be present when the initramfs runs, or some kernel modules might need to be loaded first. On my Dell XPS 9360 laptop, the NVMe system disk is already present when the initramfs starts, whereas in qemu, we need to load the virtio_pci module, followed by the virtio_scsi module. How will our userland program know which kernel modules to load? Linux kernel modules declare patterns for their supported hardware as an alias, e.g.:

initrd# grep virtio_pci lib/modules/5.4.6/modules.alias
alias pci:v00001AF4d*sv*sd*bc*sc*i* virtio_pci

Devices in sysfs have a modalias file whose content can be matched against these declarations to identify the module to load:

initrd# cat /sys/devices/pci0000:00/*/modalias
pci:v00001AF4d00001005sv00001AF4sd00000004bc00scFFi00
pci:v00001AF4d00001004sv00001AF4sd00000008bc01sc00i00
[ ]

Hence, for the initial round of module loading, it is sufficient to locate all modalias files within sysfs and load the responsible modules. Loading a kernel module can result in new devices appearing. When that happens, the kernel sends a uevent, which the uevent consumer in userspace receives via a netlink socket. Typically, this consumer is udev(7) , but in our case, it s minitrd. For each uevent messages that comes with a MODALIAS variable, minitrd will load the relevant kernel module(s). When loading a kernel module, its dependencies need to be loaded first. Dependency information is stored in the modules.dep file in a Makefile-like syntax:

initrd# grep virtio_pci lib/modules/5.4.6/modules.dep
kernel/drivers/virtio/virtio_pci.ko: kernel/drivers/virtio/virtio_ring.ko kernel/drivers/virtio/virtio.ko

To load a module, we can open its file and then call the Linux-specific finit_module(2) system call. Some modules are expected to return an error code, e.g. ENODEV or ENOENT when some hardware device is not actually present. Side note: next to the textual versions, there are also binary versions of the modules.alias and modules.dep files. Presumably, those can be queried more quickly, but for simplicitly, I have not (yet?) implemented support in minitrd.

2. Console settings: font, keyboard layout Setting a legible font is necessary for hi-dpi displays. On my Dell XPS 9360 (3200 x 1800 QHD+ display), the following works well:

initrd# setfont latarcyrheb-sun32

Setting the user s keyboard layout is necessary for entering the LUKS full-disk encryption passphrase in their preferred keyboard layout. I use the NEO layout:

initrd# loadkeys neo

3. Block device identification In the Linux kernel, block device enumeration order is not necessarily the same on each boot. Even if it was deterministic, device order could still be changed when users modify their computer s device topology (e.g. connect a new disk to a formerly unused port). Hence, it is good style to refer to disks and their partitions with stable identifiers. This also applies to boot loader configuration, and so most distributions will set a kernel parameter such as root=UUID=1fa04de7-30a9-4183-93e9-1b0061567121. Identifying the block device or partition with the specified UUID is the initramfs s job. Depending on what the device contains, the UUID comes from a different place. For example, ext4 file systems have a UUID field in their file system superblock, whereas LUKS volumes have a UUID in their LUKS header. Canonically, probing a device to extract the UUID is done by libblkid from the util-linux package, but the logic can easily be re-implemented in other languages and changes rarely. minitrd comes with its own implementation to avoid cgo or running the blkid(8) program.

4. LUKS full-disk encryption unlocking (only on encrypted systems) Unlocking a LUKS-encrypted volume is done in userspace. The kernel handles the crypto, but reading the metadata, obtaining the passphrase (or e.g. key material from a file) and setting up the device mapper table entries are done in user space.

initrd# modprobe algif_skcipher
initrd# cryptsetup luksOpen /dev/sda4 cryptroot1

After the user entered their passphrase, the root file system can be mounted:

initrd# mount /dev/dm-0 /mnt

5. Continuing the boot process (switch_root) Now that everything is set up, we need to pass execution to the init program on the root file system with a careful sequence of chdir(2) , mount(2) , chroot(2) , chdir(2) and execve(2) system calls that is explained in this busybox switch_root comment.

initrd# mount -t devtmpfs dev /mnt/dev
initrd# exec switch_root -c /dev/console /mnt /init

To conserve RAM, the files in the temporary file system to which the initramfs archive is extracted are typically deleted.

How is an initramfs generated? An initramfs image (more accurately: archive) is a compressed cpio archive. Typically, gzip compression is used, but the kernel supports a bunch of different algorithms and distributions such as Ubuntu are switching to lz4. Generators typically prepare a temporary directory and feed it to the cpio(1) program. In minitrd, we read the files into memory and generate the cpio archive using the go-cpio package. We use the pgzip package for parallel gzip compression. The following files need to go into the cpio archive:

minitrd Go userland The minitrd binary is copied into the cpio archive as /init and will be run by the kernel after extracting the archive. Like the rest of distri, minitrd is built statically without cgo, which means it can be copied as-is into the cpio archive.

Linux kernel modules Aside from the modules.alias and modules.dep metadata files, the kernel modules themselves reside in e.g. /lib/modules/5.4.6/kernel and need to be copied into the cpio archive. Copying all modules results in a 80 MiB archive, so it is common to only copy modules that are relevant to the initramfs s features. This reduces archive size to 24 MiB. The filtering relies on hard-coded patterns and module names. For example, disk encryption related modules are all kernel modules underneath kernel/crypto, plus kernel/drivers/md/dm-crypt.ko. When generating a host-only initramfs (works on precisely the computer that generated it), some initramfs generators look at the currently loaded modules and just copy those.

Console Fonts and Keymaps The kbd package s setfont(8) and loadkeys(1) programs load console fonts and keymaps from /usr/share/consolefonts and /usr/share/keymaps, respectively. Hence, these directories need to be copied into the cpio archive. Depending on whether the initramfs should be generic (work on many computers) or host-only (works on precisely the computer/settings that generated it), the entire directories are copied, or only the required font/keymap.

cryptsetup, setfont, loadkeys These programs are (currently) required because minitrd does not implement their functionality. As they are dynamically linked, not only the programs themselves need to be copied, but also the ELF dynamic linking loader (path stored in the .interp ELF section) and any ELF library dependencies. For example, cryptsetup in distri declares the ELF interpreter /ro/glibc-amd64-2.27-3/out/lib/ld-linux-x86-64.so.2 and declares dependencies on shared libraries libcryptsetup.so.12, libblkid.so.1 and others. Luckily, in distri, packages contain a lib subdirectory containing symbolic links to the resolved shared library paths (hermetic packaging), so it is sufficient to mirror the lib directory into the cpio archive, recursing into shared library dependencies of shared libraries. cryptsetup also requires the GCC runtime library libgcc_s.so.1 to be present at runtime, and will abort with an error message about not being able to call pthread_cancel(3) if it is unavailable.

time zone data To print log messages in the correct time zone, we copy /etc/localtime from the host into the cpio archive.

minitrd outside of distri? I currently have no desire to make minitrd available outside of distri. While the technical challenges (such as extending the generator to not rely on distri s hermetic packages) are surmountable, I don t want to support people s initramfs remotely. Also, I think that people s efforts should in general be spent on rallying behind dracut and making it work faster, thereby benefiting all Linux distributions that use dracut (increasingly more). With minitrd, I have demonstrated that significant speed-ups are achievable.

Conclusion It was interesting to dive into how an initramfs really works. I had been working with the concept for many years, from small tasks such as debug why the encrypted root file system is not unlocked to more complicated tasks such as set up a root file system on DRBD for a high-availability setup . But even with that sort of experience, I didn t know all the details, until I was forced to implement every little thing. As I suspected going into this exercise, dracut is much slower than it needs to be. Re-implementing its generation stage in a modern language instead of shell helps a lot. Of course, my minitrd does a bit less than dracut, but not drastically so. The overall architecture is the same. I hope my effort helps with two things:

1. As a teaching implementation: instead of wading through the various components that make up a modern initramfs (udev, systemd, various shell scripts, ), people can learn about how an initramfs works in a single place.
2. I hope the significant time difference motivates people to improve dracut.

Appendix: qemu development environment Before writing any Go code, I did some manual prototyping. Learning how other people prototype is often immensely useful to me, so I m sharing my notes here. First, I copied all kernel modules and a statically built busybox binary:

% mkdir -p lib/modules/5.4.6
% cp -Lr /ro/lib/modules/5.4.6/* lib/modules/5.4.6/
% cp ~/busybox-1.22.0-amd64/busybox sh

To generate an initramfs from the current directory, I used:

% find .   cpio -o -H newc   pigz > /tmp/initrd

In distri s Makefile, I append these flags to the QEMU invocation:

-kernel /tmp/kernel \
-initrd /tmp/initrd \
-append "root=/dev/mapper/cryptroot1 rdinit=/sh ro console=ttyS0,115200 rd.luks=1 rd.luks.uuid=63051f8a-54b9-4996-b94f-3cf105af2900 rd.luks.name=63051f8a-54b9-4996-b94f-3cf105af2900=cryptroot1 rd.vconsole.keymap=neo rd.vconsole.font=latarcyrheb-sun32 init=/init systemd.setenv=PATH=/bin rw vga=836"

The vga= mode parameter is required for loading font latarcyrheb-sun32. Once in the busybox shell, I manually prepared the required mount points and kernel modules:

ln -s sh mount
ln -s sh lsmod
mkdir /proc /sys /run /mnt
mount -t proc proc /proc
mount -t sysfs sys /sys
mount -t devtmpfs dev /dev
modprobe virtio_pci
modprobe virtio_scsi

As a next step, I copied cryptsetup and dependencies into the initramfs directory:

% for f in /ro/cryptsetup-amd64-2.0.4-6/lib/*; do full=$(readlink -f $f); rel=$(echo $full   sed 's,^/,,g'); mkdir -p $(dirname $rel); install $full $rel; done
% ln -s ld-2.27.so ro/glibc-amd64-2.27-3/out/lib/ld-linux-x86-64.so.2
% cp /ro/glibc-amd64-2.27-3/out/lib/ld-2.27.so ro/glibc-amd64-2.27-3/out/lib/ld-2.27.so
% cp -r /ro/cryptsetup-amd64-2.0.4-6/lib ro/cryptsetup-amd64-2.0.4-6/
% mkdir -p ro/gcc-libs-amd64-8.2.0-3/out/lib64/
% cp /ro/gcc-libs-amd64-8.2.0-3/out/lib64/libgcc_s.so.1 ro/gcc-libs-amd64-8.2.0-3/out/lib64/libgcc_s.so.1
% ln -s /ro/gcc-libs-amd64-8.2.0-3/out/lib64/libgcc_s.so.1 ro/cryptsetup-amd64-2.0.4-6/lib
% cp -r /ro/lvm2-amd64-2.03.00-6/lib ro/lvm2-amd64-2.03.00-6/

In busybox, I used the following commands to unlock the root file system:

modprobe algif_skcipher
./cryptsetup luksOpen /dev/sda4 cryptroot1
mount /dev/dm-0 /mnt

Rolling Stone has an insightful article about why the Christian Right supports Trump and won t stop supporting him no matter what he does [1]. Interesting article about Data Oriented Architecture [2]. Quarantine Will normalise WFH and Recession will Denormalise Jobs [3]. I guess we can always hope that after a disaster we can learn to do things better than before. Tyre wear is worse than exhaust for small particulate matter [4]. We need better tyres and legal controls over such things. Scott Santens wrote an insightful article about the need for democracy and unconditional basic income [5]. In ancient Greece, work was regarded as a curse is an extreme position but strongly supported by evidence. In his essay In Praise of Idleness, Bertrand Russell wrote Modern methods of production have given us the possibility of ease and security for all; we have chosen, instead, to have overwork for some and starvation for others. Hitherto we have continued to be as energetic as we were before there were machines; in this we have been foolish, but there is no reason to go on being foolish forever. Cory Doctorow wrote an insightful article for Locus titled A Lever Without a Fulcrum Is Just a Stick about expansions to copyright laws [6]. One of his analogies is that giving a bullied kid more lunch money just allows the bullies to steal more money, with artists being bullied kids and lunch money being the rights that are granted under copyright law. The proposed solution includes changes to labor and contract law, presumably Cory will write other articles in future giving the details of his ideas in this regard. The Register has an amusing article about the trial of a former CIA employee on trial for being the alleged vault 7 leaker [7]. Both the prosecution and the defence are building their cases around the defendent being a jerk. The article exposes poor security and poor hiring practices in the CIA. CNN has an informative article about Finland s war on fake news [8]. As Finland has long standing disputes with Russia they have had more practice at dealing with fake news than most countries. The Times of Israel has an interesting article about how the UK used German Jews to spy on German prisoners of war [9]. Cory Doctorow wrote an insightful article Data is the New Toxic Waste about how collecting personal data isn t an asset, it s a liability [10]. Ulrike Uhlig wrote an insightful article about Control Freaks , analysing the different meanings of control, both positive and negative [11]. 538 has an informative article about the value of statistical life [12]. It s about $9M per person in the US, which means a mind-boggling amount of money should be spent to save the millions of lives that will be potentially lost in a natural disaster (like Coronavirus). NPR has an interesting interview about Crypto AG, the Swiss crypto company owned by the CIA [13]. I first learned of this years ago, it s not new, but I still learned a lot from this interview.

• [1] http://tinyurl.com/r2zyrpz
• [2] https://blog.eyas.sh/2020/03/data-oriented-architecture/
• [3] https://abe-winter.github.io/2020/03/07/wfhdemic.html
• [4] http://tinyurl.com/tf4yj4m
• [5] http://tinyurl.com/y9dcnzma
• [6] http://tinyurl.com/v3mxgh5
• [7] https://www.theregister.co.uk/2020/03/05/cia_leak_trial/
• [8] http://tinyurl.com/y6cn42us
• [9] http://tinyurl.com/y67mo4rr
• [10] http://tinyurl.com/wucsgw8
• [11] https://curlybracket.net/2020/03/16/control-freaks.html
• [12] http://tinyurl.com/s6e7luk
• [13] http://tinyurl.com/qpx3dah

The following contributors got their Debian Developer accounts in the last two months:

• Allison Randal (wendar)
• Carsten Schoenert (tijuca)
• Jeremy Bicha (jbicha)
• Luca Boccassi (bluca)
• Michael Hudson-Doyle (mwhudson)
• Elana Hashman (ehashman)

The following contributors were added as Debian Maintainers in the last two months:

• Ervin Heged s
• Tom Marble
• Lukas Schwaighofer
• Philippe Thierry

Congratulations!

Confession time: I started making these posts (eons ago) because a close friend did as well, and I enjoyed reading them. But the main reason why I continue is because the primary way I have to keep track of the books I've bought and avoid duplicates is, well, grep on these posts. I should come up with a non-bullshit way of doing this, but time to do more elegant things is in short supply, and, well, it's my blog. So I'm boring all of you who read this in various places with my internal bookkeeping. I do try to at least add a bit of commentary. This one will be more tedious than most since it includes five separate Humble Bundles, which increases the volume a lot. (I just realized I'd forgotten to record those purchases from the past several months.) First, the individual books I bought directly: Ilona Andrews Sweep in Peace (sff)
Ilona Andrews One Fell Sweep (sff)
Steven Brust Vallista (sff)
Nicky Drayden The Prey of Gods (sff)
Meg Elison The Book of the Unnamed Midwife (sff)
Pat Green Night Moves (nonfiction)
Ann Leckie Provenance (sff)
Seanan McGuire Once Broken Faith (sff)
Seanan McGuire The Brightest Fell (sff)
K. Arsenault Rivera The Tiger's Daughter (sff)
Matthew Walker Why We Sleep (nonfiction)
Some new books by favorite authors, a few new releases I heard good things about, and two (Night Moves and Why We Sleep) from references in on-line articles that impressed me. The books from security bundles (this is mostly work reading, assuming I'll get to any of it), including a blockchain bundle: Wil Allsop Unauthorised Access (nonfiction)
Ross Anderson Security Engineering (nonfiction)
Chris Anley, et al. The Shellcoder's Handbook (nonfiction)
Conrad Barsky & Chris Wilmer Bitcoin for the Befuddled (nonfiction)
Imran Bashir Mastering Blockchain (nonfiction)
Richard Bejtlich The Practice of Network Security (nonfiction)
Kariappa Bheemaiah The Blockchain Alternative (nonfiction)
Violet Blue Smart Girl's Guide to Privacy (nonfiction)
Richard Caetano Learning Bitcoin (nonfiction)
Nick Cano Game Hacking (nonfiction)
Bruce Dang, et al. Practical Reverse Engineering (nonfiction)
Chris Dannen Introducing Ethereum and Solidity (nonfiction)
Daniel Drescher Blockchain Basics (nonfiction)
Chris Eagle The IDA Pro Book, 2nd Edition (nonfiction)
Nikolay Elenkov Android Security Internals (nonfiction)
Jon Erickson Hacking, 2nd Edition (nonfiction)
Pedro Franco Understanding Bitcoin (nonfiction)
Christopher Hadnagy Social Engineering (nonfiction)
Peter N.M. Hansteen The Book of PF (nonfiction)
Brian Kelly The Bitcoin Big Bang (nonfiction)
David Kennedy, et al. Metasploit (nonfiction)
Manul Laphroaig (ed.) PoC GTFO (nonfiction)
Michael Hale Ligh, et al. The Art of Memory Forensics (nonfiction)
Michael Hale Ligh, et al. Malware Analyst's Cookbook (nonfiction)
Michael W. Lucas Absolute OpenBSD, 2nd Edition (nonfiction)
Bruce Nikkel Practical Forensic Imaging (nonfiction)
Sean-Philip Oriyano CEHv9 (nonfiction)
Kevin D. Mitnick The Art of Deception (nonfiction)
Narayan Prusty Building Blockchain Projects (nonfiction)
Prypto Bitcoin for Dummies (nonfiction)
Chris Sanders Practical Packet Analysis, 3rd Edition (nonfiction)
Bruce Schneier Applied Cryptography (nonfiction)
Adam Shostack Threat Modeling (nonfiction)
Craig Smith The Car Hacker's Handbook (nonfiction)
Dafydd Stuttard & Marcus Pinto The Web Application Hacker's Handbook (nonfiction)
Albert Szmigielski Bitcoin Essentials (nonfiction)
David Thiel iOS Application Security (nonfiction)
Georgia Weidman Penetration Testing (nonfiction)
Finally, the two SF bundles: Buzz Aldrin & John Barnes Encounter with Tiber (sff)
Poul Anderson Orion Shall Rise (sff)
Greg Bear The Forge of God (sff)
Octavia E. Butler Dawn (sff)
William C. Dietz Steelheart (sff)
J.L. Doty A Choice of Treasons (sff)
Harlan Ellison The City on the Edge of Forever (sff)
Toh Enjoe Self-Reference ENGINE (sff)
David Feintuch Midshipman's Hope (sff)
Alan Dean Foster Icerigger (sff)
Alan Dean Foster Mission to Moulokin (sff)
Alan Dean Foster The Deluge Drivers (sff)
Taiyo Fujii Orbital Cloud (sff)
Hideo Furukawa Belka, Why Don't You Bark? (sff)
Haikasoru (ed.) Saiensu Fikushon 2016 (sff anthology)
Joe Haldeman All My Sins Remembered (sff)
Jyouji Hayashi The Ouroboros Wave (sff)
Sergei Lukyanenko The Genome (sff)
Chohei Kambayashi Good Luck, Yukikaze (sff)
Chohei Kambayashi Yukikaze (sff)
Sakyo Komatsu Virus (sff)
Miyuki Miyabe The Book of Heroes (sff)
Kazuki Sakuraba Red Girls (sff)
Robert Silverberg Across a Billion Years (sff)
Allen Steele Orbital Decay (sff)
Bruce Sterling Schismatrix Plus (sff)
Michael Swanwick Vacuum Flowers (sff)
Yoshiki Tanaka Legend of the Galactic Heroes, Volume 1: Dawn (sff)
Yoshiki Tanaka Legend of the Galactic Heroes, Volume 2: Ambition (sff)
Yoshiki Tanaka Legend of the Galactic Heroes, Volume 3: Endurance (sff)
Tow Ubukata Mardock Scramble (sff)
Sayuri Ueda The Cage of Zeus (sff)
Sean Williams & Shane Dix Echoes of Earth (sff)
Hiroshi Yamamoto MM9 (sff)
Timothy Zahn Blackcollar (sff)
Phew. Okay, all caught up, and hopefully won't have to dump something like this again in the near future. Also, more books than I have any actual time to read, but what else is new.

An earlier article showed that private key storage is an important problem to solve in any cryptographic system and established keycards as a good way to store private key material offline. But which keycard should we use? This article examines the form factor, openness, and performance of four keycards to try to help readers choose the one that will fit their needs. I have personally been using a YubiKey NEO, since a 2015 announcement on GitHub promoting two-factor authentication. I was also able to hook up my SSH authentication key into the YubiKey's 2048 bit RSA slot. It seemed natural to move the other subkeys onto the keycard, provided that performance was sufficient. The mail client that I use, (Notmuch), blocks when decrypting messages, which could be a serious problems on large email threads from encrypted mailing lists. So I built a test harness and got access to some more keycards: I bought a FST-01 from its creator, Yutaka Niibe, at the last DebConf and Nitrokey donated a Nitrokey Pro. I also bought a YubiKey 4 when I got the NEO. There are of course other keycards out there, but those are the ones I could get my hands on. You'll notice none of those keycards have a physical keypad to enter passwords, so they are all vulnerable to keyloggers that could extract the key's PIN. Keep in mind, however, that even with the PIN, an attacker could only ask the keycard to decrypt or sign material but not extract the key that is protected by the card's firmware.

Form factor The four keycards have similar form factors: they all connect to a standard USB port, although both YubiKey keycards have a capacitive button by which the user triggers two-factor authentication and the YubiKey 4 can also require a button press to confirm private key use. The YubiKeys feel sturdier than the other two. The NEO has withstood two years of punishment in my pockets along with the rest of my "real" keyring and there is only minimal wear on the keycard in the picture. It's also thinner so it fits well on the keyring. The FST-01 stands out from the other two with its minimal design. Out of the box, the FST-01 comes without a case, so the circuitry is exposed. This is deliberate: one of its goals is to be as transparent as possible, both in terms of software and hardware design and you definitely get that feeling at the physical level. Unfortunately, that does mean it feels more brittle than other models: I wouldn't carry it in my pocket all the time, although there is a case that may protect the key a little better, but it does not provide an easy way to hook it into a keyring. In the group picture above, the FST-01 is the pink plastic thing, which is a rubbery casing I received along with the device when I got it. Notice how the USB connectors of the YubiKeys differ from the other two: while the FST-01 and the Nitrokey have standard USB connectors, the YubiKey has only a "half-connector", which is what makes it thinner than the other two. The "Nano" form factor takes this even further and almost disappears in the USB port. Unfortunately, this arrangement means the YubiKey NEO often comes loose and falls out of the USB port, especially when connected to a laptop. On my workstation, however, it usually stays put even with my whole keyring hanging off of it. I suspect this adds more strain to the host's USB port but that's a tradeoff I've lived with without any noticeable wear so far. Finally, the NEO has this peculiar feature of supporting NFC for certain operations, as LWN previously covered, but I haven't used that feature yet. The Nitrokey Pro looks like a normal USB key, in contrast with the other two devices. It does feel a little brittle when compared with the YubiKey, although only time will tell how much of a beating it can take. It has a small ring in the case so it is possible to carry it directly on your keyring, but I would be worried the cap would come off eventually. Nitrokey devices are also two times thicker than the Yubico models which makes them less convenient to carry around on keyrings.

Open and closed designs The FST-01 is as open as hardware comes, down to the PCB design available as KiCad files in this Git repository. The software running on the card is the Gnuk firmware that implements the OpenPGP card protocol, but you can also get it with firmware implementing a true random number generator (TRNG) called NeuG (pronounced "noisy"); the device is programmable through a standard Serial Wire Debug (SWD) port. The Nitrokey Start model also runs the Gnuk firmware. However, the Nitrokey website announces only ECC and RSA 2048-bit support for the Start, while the FST-01 also supports RSA-4096. Nitrokey's founder Jan Suhr, in a private email, explained that this is because "Gnuk doesn't support RSA-3072 or larger at a reasonable speed". Its devices (the Pro, Start, and HSM models) use a similar chip to the FST-01: the STM32F103 microcontroller. Nitrokey also publishes its hardware designs, on GitHub, which shows the Pro is basically a fork of the FST-01, according to the ChangeLog. I opened the case to confirm it was using the STM MCU, something I should warn you against; I broke one of the pins holding it together when opening it so now it's even more fragile. But at least, I was able to confirm it was built using the STM32F103TBU6 MCU, like the FST-01. But this is where the comparison ends: on the back side, we find a SIM card reader that holds the OpenPGP card that, in turn, holds the private key material and does the cryptographic operations. So, in effect, the Nitrokey Pro is really a evolution of the original OpenPGP card readers. Nitrokey confirmed the OpenPGP card featured in the Pro is the same as the one shipped by the Free Software Foundation Europe (FSFE): the BasicCard built by ZeitControl. Those cards, however, are covered by NDAs and the firmware is only partially open source. This makes the Nitrokey Pro less open than the FST-01, but that's an inevitable tradeoff when choosing a design based on the OpenPGP cards, which Suhr described to me as "pretty proprietary". There are other keycards out there, however, for example the SLJ52GDL150-150k smartcard suggested by Debian developer Yves-Alexis Perez, which he prefers as it is certified by French and German authorities. In that blog post, he also said he was experimenting with the GPL-licensed OpenPGP applet implemented by the French ANSSI. But the YubiKey devices are even further away in the closed-design direction. Both the hardware designs and firmware are proprietary. The YubiKey NEO, for example, cannot be upgraded at all, even though it is based on an open firmware. According to Yubico's FAQ, this is due to "best security practices": "There is a 'no upgrade' policy for our devices since nothing, including malware, can write to the firmware." I find this decision questionable in a context where security updates are often more important than trying to design a bulletproof design, which may simply be impossible. And the YubiKey NEO did suffer from critical security issue that allowed attackers to bypass the PIN protection on the card, which raises the question of the actual protection of the private key material on those cards. According to Niibe, "some OpenPGP cards store the private key unencrypted. It is a common attitude for many smartcard implementations", which was confirmed by Suhr: "the private key is protected by hardware mechanisms which prevent its extraction and misuse". He is referring to the use of tamper resistance. After that security issue, there was no other option for YubiKey NEO users than to get a new keycard (for free, thankfully) from Yubico, which also meant discarding the private key material on the key. For OpenPGP keys, this may mean having to bootstrap the web of trust from scratch if the keycard was responsible for the main certification key. But at least the NEO is running free software based on the OpenPGP card applet and the source is still available on GitHub. The YubiKey 4, on the other hand, is now closed source, which was controversial when the new model was announced last year. It led the main Linux Foundation system administrator, Konstantin Ryabitsev, to withdraw his endorsement of Yubico products. In response, Yubico argued that this approach was essential to the security of its devices, which are now based on "a secure chip, which has built-in countermeasures to mitigate a long list of attacks". In particular, it claims that:

A commercial-grade AVR or ARM controller is unfit to be used in a security product. In most cases, these controllers are easy to attack, from breaking in via a debug/JTAG/TAP port to probing memory contents. Various forms of fault injection and side-channel analysis are possible, sometimes allowing for a complete key recovery in a shockingly short period of time.

While I understand those concerns, they eventually come down to the trust you have in an organization. Not only do we have to trust Yubico, but also hardware manufacturers and designs they have chosen. Every step in the hidden supply chain is then trusted to make correct technical decisions and not introduce any backdoors. History, unfortunately, is not on Yubico's side: Snowden revealed the example of RSA security accepting what renowned cryptographer Bruce Schneier described as a "bribe" from the NSA to weaken its ECC implementation, by using the presumably backdoored Dual_EC_DRBG algorithm. What makes Yubico or its suppliers so different from RSA Security? Remember that RSA Security used to be an adamant opponent to the degradation of encryption standards, campaigning against the Clipper chip in the first crypto wars. Even if we trust the Yubico supply chain, how can we trust a closed design using what basically amounts to security through obscurity? Publicly auditable designs are an important tradition in cryptography, and that principle shouldn't stop when software is frozen into silicon. In fact, a critical vulnerability called ROCA disclosed recently affects closed "smartcards" like the YubiKey 4 and allows full private key recovery from the public key if the key was generated on a vulnerable keycard. When speaking with Ars Technica, the researchers outlined the importance of open designs and questioned the reliability of certification:

Our work highlights the dangers of keeping the design secret and the implementation closed-source, even if both are thoroughly analyzed and certified by experts. The lack of public information causes a delay in the discovery of flaws (and hinders the process of checking for them), thereby increasing the number of already deployed and affected devices at the time of detection.

This issue with open hardware designs seems to be recurring topic of conversation on the Gnuk mailing list. For example, there was a discussion in September 2017 regarding possible hardware vulnerabilities in the STM MCU that would allow extraction of encrypted key material from the key. Niibe referred to a talk presented at the WOOT 17 workshop, where Johannes Obermaier and Stefan Tatschner, from the Fraunhofer Institute, demonstrated attacks against the STMF0 family MCUs. It is still unclear if those attacks also apply to the older STMF1 design used in the FST-01, however. Furthermore, extracted private key material is still protected by user passphrase, but the Gnuk uses a weak key derivation function, so brute-forcing attacks may be possible. Fortunately, there is work in progress to make GnuPG hash the passphrase before sending it to the keycard, which should make such attacks harder if not completely pointless. When asked about the Yubico claims in a private email, Niibe did recognize that "it is true that there are more weak points in general purpose implementations than special implementations". During the last DebConf in Montreal, Niibe explained:

If you don't trust me, you should not buy from me. Source code availability is only a single factor: someone can maliciously replace the firmware to enable advanced attacks.

Niibe recommends to "build the firmware yourself", also saying the design of the FST-01 uses normal hardware that "everyone can replicate". Those advantages are hard to deny for a cryptographic system: using more generic components makes it harder for hostile parties to mount targeted attacks. A counter-argument here is that it can be difficult for a regular user to audit such designs, let alone physically build the device from scratch but, in a mailing list discussion, Debian developer Ian Jackson explained that:

You don't need to be able to validate it personally. The thing spooks most hate is discovery. Backdooring supposedly-free hardware is harder (more costly) because it comes with greater risk of discovery. To put it concretely: if they backdoor all of them, someone (not necessarily you) might notice. (Backdooring only yours involves messing with the shipping arrangements and so on, and supposes that you specifically are of interest.)

Since that, as far as we know, the STM microcontrollers are not backdoored, I would tend to favor those devices instead of proprietary ones, as such a backdoor would be more easily detectable than in a closed design. Even though physical attacks may be possible against those microcontrollers, in the end, if an attacker has physical access to a keycard, I consider the key compromised, even if it has the best chip on the market. In our email exchange, Niibe argued that "when a token is lost, it is better to revoke keys, even if the token is considered secure enough". So like any other device, physical compromise of tokens may mean compromise of the key and should trigger key-revocation procedures.

Algorithms and performance To establish reliable performance results, I wrote a benchmark program naively called crypto-bench that could produce comparable results between the different keys. The program takes each algorithm/keycard combination and runs 1000 decryptions of a 16-byte file (one AES-128 block) using GnuPG, after priming it to get the password cached. I assume the overhead of GnuPG calls to be negligible, as it should be the same across all tokens, so comparisons are possible. AES encryption is constant across all tests as it is always performed on the host and fast enough to be irrelevant in the tests. I used the following:

• Intel(R) Core(TM) i3-6100U CPU @ 2.30GHz running Debian 9 ("stretch"/stable amd64), using GnuPG 2.1.18-6 (from the stable Debian package)
• Nitrokey Pro 0.8 (latest firmware)
• FST-01, running Gnuk version 1.2.5 (latest firmware)
• YubiKey NEO OpenPGP applet 1.0.10 (not upgradable)
• YubiKey 4 4.2.6 (not upgradable)

I ran crypto-bench for each keycard, which resulted in the following:

Algorithm	Device	Mean time (s)
ECDH-Curve25519	CPU	0.036
	FST-01	0.135
RSA-2048	CPU	0.016
	YubiKey-4	0.162
	Nitrokey-Pro	0.610
	YubiKey-NEO	0.736
	FST-01	1.265
RSA-4096	CPU	0.043
	YubiKey-4	0.875
	Nitrokey-Pro	3.150
	FST-01	8.218

There we see the performance of the four keycards I tested, compared with the same operations done without a keycard: the "CPU" device. That provides the baseline time of GnuPG decrypting the file. The first obvious observation is that using a keycard is slower: in the best scenario (FST-01 + ECC) we see a four-fold slowdown, but in the worst case (also FST-01, but RSA-4096), we see a catastrophic 200-fold slowdown. When I presented the results on the Gnuk mailing list, GnuPG developer Werner Koch confirmed those "numbers are as expected":

With a crypto chip RSA is much faster. By design the Gnuk can't be as fast - it is just a simple MCU. However, using Curve25519 Gnuk is really fast.

And yes, the FST-01 is really fast at doing ECC, but it's also the only keycard that handles ECC in my tests; the Nitrokey Start and Nitrokey HSM should support it as well, but I haven't been able to test those devices. Also note that the YubiKey NEO doesn't support RSA-4096 at all, so we can only compare RSA-2048 across keycards. We should note, however, that ECC is slower than RSA on the CPU, which suggests the Gnuk ECC implementation used by the FST-01 is exceptionally fast. In discussions about improving the performance of the FST-01, Niibe estimated the user tolerance threshold to be "2 seconds decryption time". In a new design using the STM32L432 microcontroller, Aurelien Jarno was able to bring the numbers for RSA-2048 decryption from 1.27s down to 0.65s, and for RSA-4096, from 8.22s down to 3.87s seconds. RSA-4096 is still beyond the two-second threshold, but at least it brings the FST-01 close to the YubiKey NEO and Nitrokey Pro performance levels. We should also underline the superior performance of the YubiKey 4: whatever that thing is doing, it's doing it faster than anyone else. It does RSA-4096 faster than the FST-01 does RSA-2048, and almost as fast as the Nitrokey Pro does RSA-2048. We should also note that the Nitrokey Pro also fails to cross the two-second threshold for RSA-4096 decryption. For me, the FST-01's stellar performance with ECC outshines the other devices. Maybe it says more about the efficiency of the algorithm than the FST-01 or Gnuk's design, but it's definitely an interesting avenue for people who want to deploy those modern algorithms. So, in terms of performance, it is clear that both the YubiKey 4 and the FST-01 take the prize in their own areas (RSA and ECC, respectively).

Conclusion In the above presentation, I have evaluated four cryptographic keycards for use with various OpenPGP operations. What the results show is that the only efficient way of storing a 4096-bit encryption key on a keycard would be to use the YubiKey 4. Unfortunately, I do not feel we should put our trust in such closed designs so I would argue you should either stick with 2048-bit encryption subkeys or keep the keys on disk. Considering that losing such a key would be catastrophic, this might be a good approach anyway. You should also consider switching to ECC encryption: even though it may not be supported everywhere, GnuPG supports having multiple encryption subkeys on a keyring: if one algorithm is unsupported (e.g. GnuPG 1.4 doesn't support ECC), it will fall back to a supported algorithm (e.g. RSA). Do not forget your previously encrypted material doesn't magically re-encrypt itself using your new encryption subkey, however. For authentication and signing keys, speed is not such an issue, so I would warmly recommend either the Nitrokey Pro or Start, or the FST-01, depending on whether you want to start experimenting with ECC algorithms. Availability also seems to be an issue for the FST-01. While you can generally get the device when you meet Niibe in person for a few bucks (I bought mine for around \$30 Canadian), the Seeed online shop says the device is out of stock at the time of this writing, even though Jonathan McDowell said that may be inaccurate in a debian-project discussion. Nevertheless, this issue may make the Nitrokey devices more attractive. When deciding on using the Pro or Start, Suhr offered the following advice:

In practice smart card security has been proven to work well (at least if you use a decent smart card). Therefore the Nitrokey Pro should be used for high security cases. If you don't trust the smart card or if Nitrokey Start is just sufficient for you, you can choose that one. This is why we offer both models.

So far, I have created a signing subkey and moved that and my authentication key to the YubiKey NEO, because it's a device I physically trust to keep itself together in my pockets and I was already using it. It has served me well so far, especially with its extra features like U2F and HOTP support, which I use frequently. Those features are also available on the Nitrokey Pro, so that may be an alternative if I lose the YubiKey. I will probably move my main certification key to the FST-01 and a LUKS-encrypted USB disk, to keep that certification key offline but backed up on two different devices. As for the encryption key, I'll wait for keycard performance to improve, or simply switch my whole keyring to ECC and use the FST-01 or Nitrokey Start for that purpose.

---

[The author would like to thank Nitrokey for providing hardware for testing.] This article first appeared in the Linux Weekly News.

While the adoption of OpenPGP by the general population is marginal at best, it is a critical component for the security community and particularly for Linux distributions. For example, every package uploaded into Debian is verified by the central repository using the maintainer's OpenPGP keys and the repository itself is, in turn, signed using a separate key. If upstream packages also use such signatures, this creates a complete trust path from the original upstream developer to users. Beyond that, pull requests for the Linux kernel are verified using signatures as well. Therefore, the stakes are high: a compromise of the release key, or even of a single maintainer's key, could enable devastating attacks against many machines. That has led the Debian community to develop a good grasp of best practices for cryptographic signatures (which are typically handled using GNU Privacy Guard, also known as GnuPG or GPG). For example, weak (less than 2048 bits) and vulnerable PGPv3 keys were removed from the keyring in 2015, and there is a strong culture of cross-signing keys between Debian members at in-person meetings. Yet even Debian developers (DDs) do not seem to have established practices on how to actually store critical private key material, as we can see in this discussion on the debian-project mailing list. That email boiled down to a simple request: can I have a "key dongles for dummies" tutorial? Key dongles, or keycards as we'll call them here, are small devices that allow users to store keys on an offline device and provide one possible solution for protecting private key material. In this article, I hope to use my experience in this domain to clarify the issue of how to store those precious private keys that, if compromised, could enable arbitrary code execution on millions of machines all over the world.

Why store keys offline? Before we go into details about storing keys offline, it may be useful to do a small reminder of how the OpenPGP standard works. OpenPGP keys are made of a main public/private key pair, the certification key, used to sign user identifiers and subkeys. My public key, shown below, has the usual main certification/signature key (marked SC) but also an encryption subkey (marked E), a separate signature key (S), and two authentication keys (marked A) which I use as RSA keys to log into servers using SSH, thanks to the Monkeysphere project.

    pub   rsa4096/792152527B75921E 2009-05-29 [SC] [expires: 2018-04-19]
      8DC901CE64146C048AD50FBB792152527B75921E
    uid                 [ultimate] Antoine Beaupr  <anarcat@anarc.at>
    uid                 [ultimate] Antoine Beaupr  <anarcat@koumbit.org>
    uid                 [ultimate] Antoine Beaupr  <anarcat@orangeseeds.org>
    uid                 [ultimate] Antoine Beaupr  <anarcat@debian.org>
    sub   rsa2048/B7F648FED2DF2587 2012-07-18 [A]
    sub   rsa2048/604E4B3EEE02855A 2012-07-20 [A]
    sub   rsa4096/A51D5B109C5A5581 2009-05-29 [E]
    sub   rsa2048/3EA1DDDDB261D97B 2017-08-23 [S]

All the subkeys (sub) and identities (uid) are bound by the main certification key using cryptographic self-signatures. So while an attacker stealing a private subkey can spoof signatures in my name or authenticate to other servers, that key can always be revoked by the main certification key. But if the certification key gets stolen, all bets are off: the attacker can create or revoke identities or subkeys as they wish. In a catastrophic scenario, an attacker could even steal the key and remove your copies, taking complete control of the key, without any possibility of recovery. Incidentally, this is why it is so important to generate a revocation certificate and store it offline. So by moving the certification key offline, we reduce the attack surface on the OpenPGP trust chain: day-to-day keys (e.g. email encryption or signature) can stay online but if they get stolen, the certification key can revoke those keys without having to revoke the main certification key as well. Note that a stolen encryption key is a different problem: even if we revoke the encryption subkey, this will only affect future encrypted messages. Previous messages will be readable by the attacker with the stolen subkey even if that subkey gets revoked, so the benefits of revoking encryption certificates are more limited.

Common strategies for offline key storage Considering the security tradeoffs, some propose storing those critical keys offline to reduce those threats. But where exactly? In an attempt to answer that question, Jonathan McDowell, a member of the Debian keyring maintenance team, said that there are three options: use an external LUKS-encrypted volume, an air-gapped system, or a keycard. Full-disk encryption like LUKS adds an extra layer of security by hiding the content of the key from an attacker. Even though private keyrings are usually protected by a passphrase, they are easily identifiable as a keyring. But when a volume is fully encrypted, it's not immediately obvious to an attacker there is private key material on the device. According to Sean Whitton, another advantage of LUKS over plain GnuPG keyring encryption is that you can pass the --iter-time argument when creating a LUKS partition to increase key-derivation delay, which makes brute-forcing much harder. Indeed, GnuPG 2.x doesn't have a run-time option to configure the key-derivation algorithm, although a patch was introduced recently to make the delay configurable at compile time in gpg-agent, which is now responsible for all secret key operations. The downside of external volumes is complexity: GnuPG makes it difficult to extract secrets out of its keyring, which makes the first setup tricky and error-prone. This is easier in the 2.x series thanks to the new storage system and the associated keygrip files, but it still requires arcane knowledge of GPG internals. It is also inconvenient to use secret keys stored outside your main keyring when you actually do need to use them, as GPG doesn't know where to find those keys anymore. Another option is to set up a separate air-gapped system to perform certification operations. An example is the PGP clean room project, which is a live system based on Debian and designed by DD Daniel Pocock to operate an OpenPGP and X.509 certificate authority using commodity hardware. The basic principle is to store the secrets on a different machine that is never connected to the network and, therefore, not exposed to attacks, at least in theory. I have personally discarded that approach because I feel air-gapped systems provide a false sense of security: data eventually does need to come in and out of the system, somehow, even if only to propagate signatures out of the system, which exposes the system to attacks. System updates are similarly problematic: to keep the system secure, timely security updates need to be deployed to the air-gapped system. A common use pattern is to share data through USB keys, which introduce a vulnerability where attacks like BadUSB can infect the air-gapped system. From there, there is a multitude of exotic ways of exfiltrating the data using LEDs, infrared cameras, or the good old TEMPEST attack. I therefore concluded the complexity tradeoffs of an air-gapped system are not worth it. Furthermore, the workflow for air-gapped systems is complex: even though PGP clean room went a long way, it's still lacking even simple scripts that allow signing or transferring keys, which is a problem shared by the external LUKS storage approach.

Keycard advantages The approach I have chosen is to use a cryptographic keycard: an external device, usually connected through the USB port, that stores the private key material and performs critical cryptographic operations on the behalf of the host. For example, the FST-01 keycard can perform RSA and ECC public-key decryption without ever exposing the private key material to the host. In effect, a keycard is a miniature computer that performs restricted computations for another host. Keycards usually support multiple "slots" to store subkeys. The OpenPGP standard specifies there are three subkeys available by default: for signature, authentication, and encryption. Finally, keycards can have an actual physical keypad to enter passwords so a potential keylogger cannot capture them, although the keycards I have access to do not feature such a keypad. We could easily draw a parallel between keycards and an air-gapped system; in effect, a keycard is a miniaturized air-gapped computer and suffers from similar problems. An attacker can intercept data on the host system and attack the device in the same way, if not more easily, because a keycard is actually "online" (i.e. clearly not air-gapped) when connected. The advantage over a fully-fledged air-gapped computer, however, is that the keycard implements only a restricted set of operations. So it is easier to create an open hardware and software design that is audited and verified, which is much harder to accomplish for a general-purpose computer. Like air-gapped systems, keycards address the scenario where an attacker wants to get the private key material. While an attacker could fool the keycard into signing or decrypting some data, this is possible only while the key is physically connected, and the keycard software will prompt the user for a password before doing the operation, though the keycard can cache the password for some time. In effect, it thwarts offline attacks: to brute-force the key's password, the attacker needs to be on the target system and try to guess the keycard's password, which will lock itself after a limited number of tries. It also provides for a clean and standard interface to store keys offline: a single GnuPG command moves private key material to a keycard (the keytocard command in the --edit-key interface), whereas moving private key material to a LUKS-encrypted device or air-gapped computer is more complex. Keycards are also useful if you operate on multiple computers. A common problem when using GnuPG on multiple machines is how to safely copy and synchronize private key material among different devices, which introduces new security problems. Indeed, a "good rule of thumb in a forensics lab", according to Robert J. Hansen on the GnuPG mailing list, is to "store the minimum personal data possible on your systems". Keycards provide the best of both worlds here: you can use your private key on multiple computers without actually storing it in multiple places. In fact, Mike Gerwitz went as far as saying:

For users that need their GPG key on multiple boxes, I consider a smartcard to be essential. Otherwise, the user is just furthering her risk of compromise.

Keycard tradeoffs As Gerwitz hinted, there are multiple downsides to using a keycard, however. Another DD, Wouter Verhelst clearly expressed the tradeoffs:

Smartcards are useful. They ensure that the private half of your key is never on any hard disk or other general storage device, and therefore that it cannot possibly be stolen (because there's only one possible copy of it). Smartcards are a pain in the ass. They ensure that the private half of your key is never on any hard disk or other general storage device but instead sits in your wallet, so whenever you need to access it, you need to grab your wallet to be able to do so, which takes more effort than just firing up GnuPG. If your laptop doesn't have a builtin cardreader, you also need to fish the reader from your backpack or wherever, etc.

"Smartcards" here refer to older OpenPGP cards that relied on the IEC 7816 smartcard connectors and therefore needed a specially-built smartcard reader. Newer keycards simply use a standard USB connector. In any case, it's true that having an external device introduces new issues: attackers can steal your keycard, you can simply lose it, or wash it with your dirty laundry. A laptop or a computer can also be lost, of course, but it is much easier to lose a small USB keycard than a full laptop and I have yet to hear of someone shoving a full laptop into a washing machine. When you lose your keycard, unless a separate revocation certificate is available somewhere, you lose complete control of the key, which is catastrophic. But, even if you revoke the lost key, you need to create a new one, which involves rebuilding the web of trust for the key a rather expensive operation as it usually requires meeting other OpenPGP users in person to exchange fingerprints. You should therefore think about how to back up the certification key, which is a problem that already exists for online keys; of course, everyone has a revocation certificates and backups of their OpenPGP keys... right? In the keycard scenario, backups may be multiple keycards distributed geographically. Note that, contrary to an air-gapped system, a key generated on a keycard cannot be backed up, by design. For subkeys, this is not a problem as they do not need to be backed up (except encryption keys). But, for a certification key, this means users need to generate the key on the host and transfer it to the keycard, which means the host is expected to have enough entropy to generate cryptographic-strength random numbers, for example. Also consider the possibility of combining different approaches: you could, for example, use a keycard for day-to-day operation, but keep a backup of the certification key on a LUKS-encrypted offline volume. Keycards introduce a new element into the trust chain: you need to trust the keycard manufacturer to not have any hostile code in the key's firmware or hardware. In addition, you need to trust that the implementation is correct. Keycards are harder to update: the firmware may be deliberately inaccessible to the host for security reasons or may require special software to manipulate. Keycards may be slower than the CPU in performing certain operations because they are small embedded microcontrollers with limited computing power. Finally, keycards may encourage users to trust multiple machines with their secrets, which works against the "minimum personal data" principle. A completely different approach called the trusted physical console (TPC) does the opposite: instead of trying to get private key material onto all of those machines, just have them on a single machine that is used for everything. Unlike a keycard, the TPC is an actual computer, say a laptop, which has the advantage of needing no special procedure to manage keys. The downside is, of course, that you actually need to carry that laptop everywhere you go, which may be problematic, especially in some corporate environments that restrict bringing your own devices.

Quick keycard "howto" Getting keys onto a keycard is easy enough:

1. Start with a temporary key to test the procedure:

       export GNUPGHOME=$(mktemp -d)
       gpg --generate-key
   

2. Edit the key using its user ID (UID):

       gpg --edit-key UID
   

3. Use the key command to select the first subkey, then copy it to the keycard (you can also use the addcardkey command to just generate a new subkey directly on the keycard):

       gpg> key 1
       gpg> keytocard
   

4. If you want to move the subkey, use the save command, which will remove the local copy of the private key, so the keycard will be the only copy of the secret key. Otherwise use the quit command to save the key on the keycard, but keep the secret key in your normal keyring; answer "n" to "save changes?" and "y" to "quit without saving?" . This way the keycard is a backup of your secret key.
5. Once you are satisfied with the results, repeat steps 1 through 4 with your normal keyring (unset $GNUPGHOME)

When a key is moved to a keycard, --list-secret-keys will show it as sec> (or ssb> for subkeys) instead of the usual sec keyword. If the key is completely missing (for example, if you moved it to a LUKS container), the # sign is used instead. If you need to use a key from a keycard backup, you simply do gpg --card-edit with the key plugged in, then type the fetch command at the prompt to fetch the public key that corresponds to the private key on the keycard (which stays on the keycard). This is the same procedure as the one to use the secret key on another computer.

Conclusion There are already informal OpenPGP best-practices guides out there and some recommend storing keys offline, but they rarely explain what exactly that means. Storing your primary secret key offline is important in dealing with possible compromises and we examined the main ways of doing so: either with an air-gapped system, LUKS-encrypted keyring, or by using keycards. Each approach has its own tradeoffs, but I recommend getting familiar with keycards if you use multiple computers and want a standardized interface with minimal configuration trouble. And of course, those approaches can be combined. This tutorial, for example, uses a keycard on an air-gapped computer, which neatly resolves the question of how to transmit signatures between the air-gapped system and the world. It is definitely not for the faint of heart, however. Once one has decided to use a keycard, the next order of business is to choose a specific device. That choice will be addressed in a followup article, where I will look at performance, physical design, and other considerations.

This article first appeared in the Linux Weekly News.

While the adoption of OpenPGP by the general population is marginal at best, it is a critical component for the security community and particularly for Linux distributions. For example, every package uploaded into Debian is verified by the central repository using the maintainer's OpenPGP keys and the repository itself is, in turn, signed using a separate key. If upstream packages also use such signatures, this creates a complete trust path from the original upstream developer to users. Beyond that, pull requests for the Linux kernel are verified using signatures as well. Therefore, the stakes are high: a compromise of the release key, or even of a single maintainer's key, could enable devastating attacks against many machines. That has led the Debian community to develop a good grasp of best practices for cryptographic signatures (which are typically handled using GNU Privacy Guard, also known as GnuPG or GPG). For example, weak (less than 2048 bits) and vulnerable PGPv3 keys were removed from the keyring in 2015, and there is a strong culture of cross-signing keys between Debian members at in-person meetings. Yet even Debian developers (DDs) do not seem to have established practices on how to actually store critical private key material, as we can see in this discussion on the debian-project mailing list. That email boiled down to a simple request: can I have a "key dongles for dummies" tutorial? Key dongles, or keycards as we'll call them here, are small devices that allow users to store keys on an offline device and provide one possible solution for protecting private key material. In this article, I hope to use my experience in this domain to clarify the issue of how to store those precious private keys that, if compromised, could enable arbitrary code execution on millions of machines all over the world.

Why store keys offline? Before we go into details about storing keys offline, it may be useful to do a small reminder of how the OpenPGP standard works. OpenPGP keys are made of a main public/private key pair, the certification key, used to sign user identifiers and subkeys. My public key, shown below, has the usual main certification/signature key (marked SC) but also an encryption subkey (marked E), a separate signature key (S), and two authentication keys (marked A) which I use as RSA keys to log into servers using SSH, thanks to the Monkeysphere project.

    pub   rsa4096/792152527B75921E 2009-05-29 [SC] [expires: 2018-04-19]
      8DC901CE64146C048AD50FBB792152527B75921E
    uid                 [ultimate] Antoine Beaupr  <anarcat@anarc.at>
    uid                 [ultimate] Antoine Beaupr  <anarcat@koumbit.org>
    uid                 [ultimate] Antoine Beaupr  <anarcat@orangeseeds.org>
    uid                 [ultimate] Antoine Beaupr  <anarcat@debian.org>
    sub   rsa2048/B7F648FED2DF2587 2012-07-18 [A]
    sub   rsa2048/604E4B3EEE02855A 2012-07-20 [A]
    sub   rsa4096/A51D5B109C5A5581 2009-05-29 [E]
    sub   rsa2048/3EA1DDDDB261D97B 2017-08-23 [S]

All the subkeys (sub) and identities (uid) are bound by the main certification key using cryptographic self-signatures. So while an attacker stealing a private subkey can spoof signatures in my name or authenticate to other servers, that key can always be revoked by the main certification key. But if the certification key gets stolen, all bets are off: the attacker can create or revoke identities or subkeys as they wish. In a catastrophic scenario, an attacker could even steal the key and remove your copies, taking complete control of the key, without any possibility of recovery. Incidentally, this is why it is so important to generate a revocation certificate and store it offline. So by moving the certification key offline, we reduce the attack surface on the OpenPGP trust chain: day-to-day keys (e.g. email encryption or signature) can stay online but if they get stolen, the certification key can revoke those keys without having to revoke the main certification key as well. Note that a stolen encryption key is a different problem: even if we revoke the encryption subkey, this will only affect future encrypted messages. Previous messages will be readable by the attacker with the stolen subkey even if that subkey gets revoked, so the benefits of revoking encryption certificates are more limited.

Common strategies for offline key storage Considering the security tradeoffs, some propose storing those critical keys offline to reduce those threats. But where exactly? In an attempt to answer that question, Jonathan McDowell, a member of the Debian keyring maintenance team, said that there are three options: use an external LUKS-encrypted volume, an air-gapped system, or a keycard. Full-disk encryption like LUKS adds an extra layer of security by hiding the content of the key from an attacker. Even though private keyrings are usually protected by a passphrase, they are easily identifiable as a keyring. But when a volume is fully encrypted, it's not immediately obvious to an attacker there is private key material on the device. According to Sean Whitton, another advantage of LUKS over plain GnuPG keyring encryption is that you can pass the --iter-time argument when creating a LUKS partition to increase key-derivation delay, which makes brute-forcing much harder. Indeed, GnuPG 2.x doesn't have a run-time option to configure the key-derivation algorithm, although a patch was introduced recently to make the delay configurable at compile time in gpg-agent, which is now responsible for all secret key operations. The downside of external volumes is complexity: GnuPG makes it difficult to extract secrets out of its keyring, which makes the first setup tricky and error-prone. This is easier in the 2.x series thanks to the new storage system and the associated keygrip files, but it still requires arcane knowledge of GPG internals. It is also inconvenient to use secret keys stored outside your main keyring when you actually do need to use them, as GPG doesn't know where to find those keys anymore. Another option is to set up a separate air-gapped system to perform certification operations. An example is the PGP clean room project, which is a live system based on Debian and designed by DD Daniel Pocock to operate an OpenPGP and X.509 certificate authority using commodity hardware. The basic principle is to store the secrets on a different machine that is never connected to the network and, therefore, not exposed to attacks, at least in theory. I have personally discarded that approach because I feel air-gapped systems provide a false sense of security: data eventually does need to come in and out of the system, somehow, even if only to propagate signatures out of the system, which exposes the system to attacks. System updates are similarly problematic: to keep the system secure, timely security updates need to be deployed to the air-gapped system. A common use pattern is to share data through USB keys, which introduce a vulnerability where attacks like BadUSB can infect the air-gapped system. From there, there is a multitude of exotic ways of exfiltrating the data using LEDs, infrared cameras, or the good old TEMPEST attack. I therefore concluded the complexity tradeoffs of an air-gapped system are not worth it. Furthermore, the workflow for air-gapped systems is complex: even though PGP clean room went a long way, it's still lacking even simple scripts that allow signing or transferring keys, which is a problem shared by the external LUKS storage approach.

Keycard advantages The approach I have chosen is to use a cryptographic keycard: an external device, usually connected through the USB port, that stores the private key material and performs critical cryptographic operations on the behalf of the host. For example, the FST-01 keycard can perform RSA and ECC public-key decryption without ever exposing the private key material to the host. In effect, a keycard is a miniature computer that performs restricted computations for another host. Keycards usually support multiple "slots" to store subkeys. The OpenPGP standard specifies there are three subkeys available by default: for signature, authentication, and encryption. Finally, keycards can have an actual physical keypad to enter passwords so a potential keylogger cannot capture them, although the keycards I have access to do not feature such a keypad. We could easily draw a parallel between keycards and an air-gapped system; in effect, a keycard is a miniaturized air-gapped computer and suffers from similar problems. An attacker can intercept data on the host system and attack the device in the same way, if not more easily, because a keycard is actually "online" (i.e. clearly not air-gapped) when connected. The advantage over a fully-fledged air-gapped computer, however, is that the keycard implements only a restricted set of operations. So it is easier to create an open hardware and software design that is audited and verified, which is much harder to accomplish for a general-purpose computer. Like air-gapped systems, keycards address the scenario where an attacker wants to get the private key material. While an attacker could fool the keycard into signing or decrypting some data, this is possible only while the key is physically connected, and the keycard software will prompt the user for a password before doing the operation, though the keycard can cache the password for some time. In effect, it thwarts offline attacks: to brute-force the key's password, the attacker needs to be on the target system and try to guess the keycard's password, which will lock itself after a limited number of tries. It also provides for a clean and standard interface to store keys offline: a single GnuPG command moves private key material to a keycard (the keytocard command in the --edit-key interface), whereas moving private key material to a LUKS-encrypted device or air-gapped computer is more complex. Keycards are also useful if you operate on multiple computers. A common problem when using GnuPG on multiple machines is how to safely copy and synchronize private key material among different devices, which introduces new security problems. Indeed, a "good rule of thumb in a forensics lab", according to Robert J. Hansen on the GnuPG mailing list, is to "store the minimum personal data possible on your systems". Keycards provide the best of both worlds here: you can use your private key on multiple computers without actually storing it in multiple places. In fact, Mike Gerwitz went as far as saying:

For users that need their GPG key on multiple boxes, I consider a smartcard to be essential. Otherwise, the user is just furthering her risk of compromise.

Keycard tradeoffs As Gerwitz hinted, there are multiple downsides to using a keycard, however. Another DD, Wouter Verhelst clearly expressed the tradeoffs:

Smartcards are useful. They ensure that the private half of your key is never on any hard disk or other general storage device, and therefore that it cannot possibly be stolen (because there's only one possible copy of it). Smartcards are a pain in the ass. They ensure that the private half of your key is never on any hard disk or other general storage device but instead sits in your wallet, so whenever you need to access it, you need to grab your wallet to be able to do so, which takes more effort than just firing up GnuPG. If your laptop doesn't have a builtin cardreader, you also need to fish the reader from your backpack or wherever, etc.

"Smartcards" here refer to older OpenPGP cards that relied on the IEC 7816 smartcard connectors and therefore needed a specially-built smartcard reader. Newer keycards simply use a standard USB connector. In any case, it's true that having an external device introduces new issues: attackers can steal your keycard, you can simply lose it, or wash it with your dirty laundry. A laptop or a computer can also be lost, of course, but it is much easier to lose a small USB keycard than a full laptop and I have yet to hear of someone shoving a full laptop into a washing machine. When you lose your keycard, unless a separate revocation certificate is available somewhere, you lose complete control of the key, which is catastrophic. But, even if you revoke the lost key, you need to create a new one, which involves rebuilding the web of trust for the key a rather expensive operation as it usually requires meeting other OpenPGP users in person to exchange fingerprints. You should therefore think about how to back up the certification key, which is a problem that already exists for online keys; of course, everyone has a revocation certificates and backups of their OpenPGP keys... right? In the keycard scenario, backups may be multiple keycards distributed geographically. Note that, contrary to an air-gapped system, a key generated on a keycard cannot be backed up, by design. For subkeys, this is not a problem as they do not need to be backed up (except encryption keys). But, for a certification key, this means users need to generate the key on the host and transfer it to the keycard, which means the host is expected to have enough entropy to generate cryptographic-strength random numbers, for example. Also consider the possibility of combining different approaches: you could, for example, use a keycard for day-to-day operation, but keep a backup of the certification key on a LUKS-encrypted offline volume. Keycards introduce a new element into the trust chain: you need to trust the keycard manufacturer to not have any hostile code in the key's firmware or hardware. In addition, you need to trust that the implementation is correct. Keycards are harder to update: the firmware may be deliberately inaccessible to the host for security reasons or may require special software to manipulate. Keycards may be slower than the CPU in performing certain operations because they are small embedded microcontrollers with limited computing power. Finally, keycards may encourage users to trust multiple machines with their secrets, which works against the "minimum personal data" principle. A completely different approach called the trusted physical console (TPC) does the opposite: instead of trying to get private key material onto all of those machines, just have them on a single machine that is used for everything. Unlike a keycard, the TPC is an actual computer, say a laptop, which has the advantage of needing no special procedure to manage keys. The downside is, of course, that you actually need to carry that laptop everywhere you go, which may be problematic, especially in some corporate environments that restrict bringing your own devices.

Quick keycard "howto" Getting keys onto a keycard is easy enough:

1. Start with a temporary key to test the procedure:

       export GNUPGHOME=$(mktemp -d)
       gpg --generate-key
   

2. Edit the key using its user ID (UID):

       gpg --edit-key UID
   

3. Use the key command to select the first subkey, then copy it to the keycard (you can also use the addcardkey command to just generate a new subkey directly on the keycard):

       gpg> key 1
       gpg> keytocard
   

4. If you want to move the subkey, use the save command, which will remove the local copy of the private key, so the keycard will be the only copy of the secret key. Otherwise use the quit command to save the key on the keycard, but keep the secret key in your normal keyring; answer "n" to "save changes?" and "y" to "quit without saving?" . This way the keycard is a backup of your secret key.
5. Once you are satisfied with the results, repeat steps 1 through 4 with your normal keyring (unset $GNUPGHOME)

When a key is moved to a keycard, --list-secret-keys will show it as sec> (or ssb> for subkeys) instead of the usual sec keyword. If the key is completely missing (for example, if you moved it to a LUKS container), the # sign is used instead. If you need to use a key from a keycard backup, you simply do gpg --card-edit with the key plugged in, then type the fetch command at the prompt to fetch the public key that corresponds to the private key on the keycard (which stays on the keycard). This is the same procedure as the one to use the secret key on another computer.

Conclusion There are already informal OpenPGP best-practices guides out there and some recommend storing keys offline, but they rarely explain what exactly that means. Storing your primary secret key offline is important in dealing with possible compromises and we examined the main ways of doing so: either with an air-gapped system, LUKS-encrypted keyring, or by using keycards. Each approach has its own tradeoffs, but I recommend getting familiar with keycards if you use multiple computers and want a standardized interface with minimal configuration trouble. And of course, those approaches can be combined. This tutorial, for example, uses a keycard on an air-gapped computer, which neatly resolves the question of how to transmit signatures between the air-gapped system and the world. It is definitely not for the faint of heart, however. Once one has decided to use a keycard, the next order of business is to choose a specific device. That choice will be addressed in a followup article, where I will look at performance, physical design, and other considerations.

This article first appeared in the Linux Weekly News.

Here is my monthly update covering what I have been doing in the free software world in August 2017 (previous month):

• Created ZeroCoolOS, a live operating system that plays the film Hackers (1995) on a continuous loop.
• Sent a patch for pristine-tar to allow storage of detached upstream signatures. (#871809)
• Worked more on Lintian, a static analysis tool for Debian packages, reporting on various errors, omissions and quality-assurance issues to the maintainer (previous changes):
  • Fix an apache2-unparsable-dependency false positive by allowing periods in dependency names. (#873701)
  • Ignore "repacked" packages when checking for upstream source tarball signatures as they will never match.
  • Downgrade the severity of orig-tarball-missing-upstream-signature. (#870722)
  • From a suggestion by Theodore Ts'o, expand the explanation of orig-tarball-missing-upstream-signature to include the location of where dpkg-source looks.
  • Address a number of issues in the copyright-year-in-future tag including preventing false positives in port numbers, email addresses, ISO standard numbers and street addresses (#869788), as well as "meta" or testing statements (#873323). In addition, report all violating years in a line and expand the testsuite.
  • Don't match quoted "FIXME" variants of file-contains-fixme-placeholder (#870199), avoid checking copyright_hints files (#872843) and downgrade the tag's severity.
  • Apply a patch from Alex Muntada to recommend "substr" over of "substring" in mentions-deprecated-usr-lib-perl5-directory. (#871767)
  • Prevent missing-build-dependency-for-dh_-command false positives exposed by following the advice in useless-autoreconf-build-depends. (#869541)
  • Ensure readme-debian-contains-debmake-template also checks for files containing "Automatically generated by debmake".
  • Check python3-foo packages have a Section: python, not just python2-foo. (#870272)
  • Check for packages shipping compiled Java class files. (#873211)
  • Additionally consider .cljc files to avoid codeless-jar warnings. (#870649)
  • Prevent desktop-entry-lacks-keywords-entry false positives for Link and Directory-style .desktop files. (#873702)
  • Split out Python checks from checks/scripts.pm check to a new, source check of type source.
  • Check for python-foo without a corresponding python3-foo package. (#870681)
  • Complain about packages that Build-Depend on python-sphinx only. (#870730)
  • Warn about packages that alternatively Build-Depend on the Python 2 and Python 3 versions of Sphinx. (#870758)
  • Check for packages that depend on Python 2.x. (#870822)
  • Correct false positives in unconditional-use-of-dpkg-statoverride by detecting "if !" as a shell prefix. (#869587)
  • Alert on for missing calls to dpkg-maintscript-helper(1) in maintainer scripts. (#872042)
  • Check for packages using sensible-utils without declaring a dependency after splitting from debianutils. (#872611)
  • Warn about scripts using nodejs as an interpreter now that the nodejs script provides /usr/bin/node. (#873096)
  • Remove recommendations to add a Testsuite: autopkgtest field to debian/control and emit a new tag the package if it does so. (#865531)
  • Recognise autopkgtest-pkg-elpa as a valid test suite. (#873458)
  • Add note to /etc/bash_completion.d's obsolete path warning output regarding stricter filename requirements. (#814599)
  • Add 4.0.1 and 4.1.0 as known Policy standards versions.
  • Apply a patch from Maia Everett to avoid British spellings under the en_US locale. (#868897)
  • Stop emitting maintainer,uploader -address-causes-mail-loops for @packages.debian.org addresses. (#871575)
  • Modify Lintian::Data's all subroutine to always return keys in insertion order.
  • Apply a patch from Steve Langasek to accomodate binutils outputting symbols in a different format on the ppc64el architecture. (#869750)
  • Add an explicit test for packages including external fonts via the Google Font and TypeKit APIs. (#873434)
  • Add missing entries in internal Test-For fields to make development/testing workflow less error-prone.
• Sent three pull requests to git-buildpackage, a tool to assist in Debian packaging from Git repositories:
  • Make pq --abbrev= configurable. (#872351)
  • Use build profiles to avoid installation of test dependencies. (#31)
  • Correct "allow to" grammar. (#30)
• Updated travis.debian.net (my hosted service for projects that host their Debian packaging on GitHub to use the Travis CI continuous integration platform for testing):
  • Move away from deb.debian.org; Travis appears to be using a HTTP proxy that strips SRV records. (commit)
  • Highlight double quotes are required for TRAVIS_DEBIAN_EXTRA_REPOSITORY. (commit)
  • Use force-unsafe-io. (commit)
  • Clarify docs when upstream already has a travis.yml file. (#46)
  • Make documentation easier to copy-paste. (commit)
• Merged a pull request in django-slack, my library to easily post messages to the Slack group-messaging utility, where instantiation of a SlackException was failing. (#71)
• Assigned two pull requests to the Redis key-value database store to correct "did not received" and "faield" typos. (#4216 & #4215).

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