Cleaning up X server warnings So I was sitting in the Narita airport with a couple of other free software developers merging X server patches. One of the developers was looking over my shoulder while the X server was building and casually commented on the number of warnings generated by the compiler. I felt like I had invited someone into my house without cleaning for months embarrassed and ashamed that we d let the code devolve into this state. Of course, we ve got excuses the X server code base is one of the oldest pieces of regularly used free software in existence. It was started before ANSI-C was codified. No function prototypes, no const , no void * , no enums or stdint.h. There may be a few developers out there who remember those days (fondly, of course), but I think most of us are glad that our favorite systems language has gained a lot of compile-time checking in the last 25 years. We ve spent time in the past adding function prototypes and cleaning up other warnings, but there was never a point at which the X server compiled without any warnings. More recently, we ve added a pile of new warning flags when compiling the X server which only served to increase the number of warnings dramatically. The current situation With the master branch of the X server and released versions of the dependencies, we generate 1047 warnings in the default build. -Wcast-qual considered chatty The GCC flag, -Wcast-qual, complains when you cast a pointer and change the const qualifier status. A very common thing for the X server to do is declare pointers as const to mark them as immutable once assigned. Often, the relevant data is actually constructed once at startup in allocated memory and stored to the data structure. During server reset, that needs to be freed, but free doesn t take a const pointer, so we cast to (void *), which -Wcast-qual then complains about. Loudly. Of the 1047 warnings, 380 of them are generated by this one warning flag. I ve gone ahead and just disabled it in util/macros for now. String constants are a pain The X server uses string constants to initialize defaults for font paths, configuration options, font names along with a host of other things. These end up getting stored in variables that can also take allocated storage. I ve gone ahead and declared the relevant objects as const and then fixed the code to suit. I don t have a count of the number of warnings these changes fixed; they were scattered across dozens of X server directories, and I was fixing one directory at a time, but probably more than half of the remaining warnings were of this form. And a host of other warnings Fixing the rest of the warnings was mostly a matter of stepping through them one at a time and actually adjusting the code. Shadowed declarations, unused values, redundant declarations and missing printf attributes were probably the bulk of them though. Changes to external modules Instead of just hacking the X server code, I ve created patches for other modules where necessary to fix the problems in the right place.

• proto/fontsproto. Declares FontPathElement names as const char *
• mesa/drm. Adds printf attribute to the debug_print function
• util/macros. Removes -Wcast-qual from the default warning set.

Getting the bits In case it wasn t clear, the X server build now generates zero warnings on my machine. I m hoping that this will also be true for other people. Patches are available at:

xserver - git://people.freedesktop.org/~keithp/xserver warning-fixes
fontsproto - git://people.freedesktop.org/~keithp/fontsproto fontsproto-next
mesa/drm - git://people.freedesktop.org/~keithp/drm warning-fixes
util/macros - already upstream on master

Keeping our house clean Of course, these patches are all waiting until 1.15 ships so that we don t accidentally break something important. However, once they re merged, I ll be bouncing any patches which generate warnings on my system, and if other people find warnings when they build, I ll expect them to send patches as well. Now to go collect the tea cups in my office and get them washed along with the breakfast dishes so I won t be embarrassed if some free software developers show up for lunch today.

Fingerprints and Key IDsOpenPGPv4 fingerprints are made from an SHA-1 digest over the key's public key material, creation date, and some boilerplate. SHA-1 digests are 160 bits in length. The "long key ID" of a key is the last 64 bits of the key's fingerprint. The "short key ID" of a key is the last 32 bits of the key's fingerprint. You can see both of the key IDs as a hash in and of themselves, as "32-bit truncated SHA-1" is a sort of hash (albeit not a cryptographically secure one). I'm arguing here that short Key IDs and long Key IDs are actually useless, and we should stop using them entirely where we can do so. We certainly should not be exposing normal human users to them. (Note that I am not arguing that OpenPGP v4 fingerprints themselves are cryptographically insecure. I do not believe that there are any serious cryptographic risks currently associated with OpenPGP v4 fingerprints. This post is about Key IDs specifically, not fingerprints.)Key IDs have serious problemsAsheesh pointed out two years ago that OpenPGP short key IDs are bad because they are trivial to replicate. This is called a preimage attack against the short key ID (which is just a truncated fingerprint). Today, David Leon Gil demonstrated that a collision attack against the long key ID is also trivial. A collision attack differs from a preimage attack in that the attacker gets to generate two different things that both have the same digest. Collision attacks are easier than preimage attacks because of the birthday paradox. dlg's colliding keys are not a surprise, but hopefully the explicit demonstration can serve as a wakeup call to help us improve our infrastructure. So this is not a way to spoof a specific target's long key ID on its own. But it indicates that it's more of a worry than most people tend to think about or plan for. And remember that for a search space as small as 64-bits (the long key ID), if you want to find a pre-image against any one of 2k keys, your search is actually only in a (64-k)-bit space to find a single pre-image. The particularly bad news: gpg doesn't cope well with the two keys that have the same long key ID:

0 dkg@alice:~$ gpg --import x
gpg: key B8EBE1AF: public key "9E669861368BCA0BE42DAF7DDDA252EBB8EBE1AF" imported
gpg: Total number processed: 1
gpg:               imported: 1  (RSA: 1)
0 dkg@alice:~$ gpg --import y
gpg: key B8EBE1AF: doesn't match our copy
gpg: Total number processed: 1
2 dkg@alice:~$ 

This probably also means that caff (from the signing-party package) will also choke when trying to deal with these two keys. I'm sure there are other OpenPGP-related tools that will fail in the face of two keys with matching 64-bit key IDs. We should not use Key IDs I am more convinced than ever that key IDs (both short and long) are actively problematic to real-world use of OpenPGP. We want two things from a key management framework: unforgability, and human-intelligible handles. Key IDs fail at both.

• Fingerprints are unforgable (as much as SHA-1's preimage resistance, anyway -- that's a separate discussion), but they aren't human-intelligible.
• User IDs are human-intelligible, and they are unforgable if we can rely on a robust keysigning network.
• Key IDs (both short and long) are neither human-intelligible nor unforgable (regardless of existence of a keysigning network), so they are the worst of all possible worlds.

So reasonable tools should not expose either short or long key IDs to users, or use them internally if they can avoid them. They do not have any properties we want, and in the worst case, they actively mislead people or lead them into harm. What reasonable tool should do that? How to replace Key IDs If we're not going to use Key IDs, what should we do instead? For anything human-facing, we should be using human-intelligible things like user IDs and creation dates. These are trivial to forge, but people can relate to them. This is better than offering the user something that is also trivial to forge, but that people cannot relate to. The job of any key management UI should be to interpret the cryptographic assurances provided by the certifications and present that to the user in a comprehensible way. For anything not human-facing (e.g. key management data storage, etc), we should be using the full key itself. We'll also want to store the full fingerprint as an index, since that is used for communication and key exchange (e.g. on calling cards). There remain parts of the spec (e.g. PK-ESK, Issuer subpackets) that make some use of the long key ID in ways that provide some measure of convenience but no real cryptographic security. We should fix the spec to stop using those, and either remove them entirely, or replace them with the full fingerprints. These fixes are not as urgent as the user-facing changes or the critical internal indexing fixes, though. Key IDs are not useful. We should stop using them.Tags: collision, crypto, gpg, openpgp, pgp, security

Today, here in the UK, the date is 11/12/13. Today, here in Edinburgh, I we became married.

I've already promised I will make no more than two jokes, ever, about "owning a wife". I will save them for suitable occasions.

Once more, I m going to FOSDEM 2014, the largest Free/Libre/Open Source Software event in Europe (5,000 attendants every year). As usual, I will be in charge of the Desktops DevRoom, together with our friends from Gnome (Christophe Fergeau), Unity (Didier Roche), Enlightenment (Philippe Caseiro) and others. See you in Brussels 1-2 February 2014! BTW, have you already submitted your talk proposal for the Desktops DevRoom? The deadline (15th December) is very close! Do not wait any more!!! See the details here: FOSDEM 2014 Desktops DevRoom Call for Talks

I ve come up with some new favorites this season. The boys and Laura were around for all three, and I am happy to report there were many kitchen smiles over these! From-Scratch Hot Chocolate There s something about hot chocolate made from scratch, with chocolate melted into milk, instead of a powder stirred in. It takes quite a bit more time, and probably has more calories, but it is quite delicious. The key to a delicious result where milk is concerned is to take things slow and keep stirring. You don t want the chocolate to scorch at the bottom of the pan. Heating up the milk before the chocolate should help things mix in more easily as well.

• Begin with 3 cups milk and 1 cup heavy whipping cream. Heat slowly over moderate to low heat, stirring periodically. Once you see bubbles start to form around the edges, it is plenty hot (or even a bit more hot than it needs to be).
• Add one cup of semisweet chocolate chips, 1 teaspoon sugar, and 1/2 tsp vanilla extract.
• Stir constantly until all the chocolate is melted and well mixed. There will still be some small bits of chocolate within, but if it is all done slowly like this, the chocolate should be pretty well melted.

The basis for this recipe was here, and it called for 2 cups milk and 2 cups half-and-half. I trust my heavy whipping cream was fine! <grin> There are also some other variations on that site. This nearly made my little cast iron kettle overflow, so next time I made a 3/4 recipe. Hot Spiced Cider We put up a Christmas tree yesterday, so I thought hot spiced cider would be perfect for the occasion. I went searching for recipes, and many of them called for cloves (which have to be sifted out later or put in a spice bag). I wasn t going to have time to delay two boys from setting up a Christmas tree long enough for that, so I found this basic recipe to work well. However, I, as usual, made some modifications ;-)

• Warm 4 cups apple cider (not juice, as the recipe suggests) in a pot.
• Add 1/2 tsp cinnamon
• Add 1/4 tsp nutmeg or allspice (I used allspice because I was mysteriously out of nutmeg, but will probably use nutmeg next time)
• Add 1 tbsp brown sugar
• Stir constantly until sufficiently dissolved. Pour immediately before drinking, as the contents will tend to separate.

Mmmmm . yum . Turkey or Chicken Noodle Soup The annual what to do with all that leftover turkey quest strikes again. I like chicken noodle soup, so why not a turkey noodle soup done the same way? Here s what I used, roughly, in my large 6-quart cast iron cooking pot (aka Dutch oven ):

• 9 cups chicken/turkey broth. Your own if you have it, or the canned variety works. Or make your own with boullion if you have it.
• 2 chopped yellow onions. (I added half a chopped red onion as well because I had it sitting around. Nobody complained, but 2.5 onions was a little much.)
• 4 tsp fresh basil or 1 tsp dried basil
• 4 tsp fresh oregano or 1 tsp dried oregano
• 1/2 tsp pepper
• 1/2 tsp salt
• 1 tsp beef bouillon
• 2 bay leaves
• 20 oz frozen mixed vegetables (I d probably add more than that next year; this wasn t quite enough)
• Plenty of wide egg noodles. The recipe I used called for 1 cup, which was laughably inadequate. I just dumped until it looked right, and then the package was almost empty so I dumped the rest in too.
• 4 cups cooked turkey or chicken, cubed (a kitchen scissors makes quick work of that)
• Two 14.5-oz cans diced tomatoes (do not drain)

Start with the broth, onion, basil, oregano, pepper, and bay leaf. Heat up the mixture and add the vegetables. Bring it to boiling, then add the uncooked noodles. Return to boiling, then reduce heat, cover, and simmer for 8 minutes. Add the turkey or chicken and diced tomatoes, and simmer until hot enough to serve. The nice thing about soups is that they freeze well and make great winter leftovers. This recipe makes quite a lot of soup; you may wish to halve it. This recipe was adapted from one in a Better Homes & Gardens cookbook.

My ASUS Transformer TF101 had suddenly started flickering in all sorts of funny colors some weeks ago. As tapping it gently on the table in the right angle made the problem go away temporarily, it was clear the problem was about a loose cable, or some other hardware connection issue. As I needed to go on a business trip the other day, I didn't look up the warranty expiration day until later that week. Then, Murphy struck: the tablet was now 2 years + 1 day old! Calling ASUS, some friendly guy there suggested I still tried to get ASUS to accept it for warranty, because the tablet had been with them last year for 5 days, so if they added that, it would still be within the warranty period. I filled out the RMA form, but one hour later the reply was they rejected it because it was out of warranty. Another guy on the phone then said they would probably only do the adding if it had been with them for maybe 10 days, or actually really 30 days, or whatever. Some googling suggested that the loose cable theory was indeed worth a try, so I took it apart. Thanks to a forum post I could then locate the display connector and fix it. Putting the case back together was actually harder than disassembling it because some plastic bits got stuck, but now everything is back to normal.

There has been a lot of discussion recently about the concept of a Basic Income (Wikipedia), largely due to the efforts to change the Swiss constitution to provide a Basic Income [1]. The concept of a Basic Income is that residents get a fixed payment without having to be sick, disabled, looking for work, or eligible for other forms of social security. A Basic Income wouldn t replace all other forms of social security, one of the most obvious examples is that sick people will often need money for medical care in additional to living expenses. Also I believe that it shouldn t be means tested in any way. I think that one of the problems with current payment schemes is that there are complex eligibility criteria which require effort for the applicant and for government agencies to prevent accidental or fraudulent over-payment. The tax rates could be raised slightly to make it revenue neutral. Newstart In Australia the main form of social security for unemployed people at the moment is called Newstart [2]. Currently Newstart payments range from a maximum of $501 per fortnight for a single person ($13,026 per annum), to a maximum of $699.90 per fortnight for someone who is a carer. The Newstart payments start to decrease if the recipient earns more than $62 per fortnight. The minimum wage in Australia is $16.37 per hour for permanent work or $20.30 for casual work [3]. So if someone works for more than 3 hours at a casual rate (and I can t imagine 4 hours a fortnight being anything other than casual) then their Newstart payments will decrease. The payment decreases are fairly significant, for every dollar that is earned about 50 cents will be deducted from the payments. That s a great incentive to either avoid opportunities to do part-time work or to do cash-only work that s outside the tax system. The most obvious way of implementing a Basic Income would be to replace Newstart. Then anyone who is in that situation would be free to just not get a job which would be OK IMHO as people who don t want to work probably wouldn t do a good job if the government forced them to get a job. People who are unemployed who want to work could work as much as they want and scale up according to what their employer asks and how much money they need. Currently the full-time minimum wage is $622.20 per week (I m not sure exactly how they get that from $16.37). That s almost 2.5* the Newstart allowance for a single person (but less than twice the Newstart allowance for a carer). While Newstart (and the other forms of social security) don t provide a great income, it seems that the difference between Newstart and the minimum wage isn t that great particularly when you consider that working involves some expenses for travel etc. There doesn t seem to be a great financial incentive for someone to leave Newstart and get a minimum wage job. People Who Want Social Security Some people think it s great to get government payments while others find it embarrassing to need such payments and won t necessarily apply if they are eligible. I think that the current system of forcing people to apply for social security is a way of discouraging people who find themselves unexpectedly in a difficult situation but doesn t discourage people who are happy not to work. This seems to effectively reduce the incidence of payments to the people who most tax-payers would regard as the most worthy recipients. Economics Charles Stross wrote about some ideas related to this [4]. He suggests that as the workforce participation has been steadily reducing due to technology we should move to a social model that isn t based around working to live but working to buy luxuries that aren t covered by the Basic Income. One of the many economic changes related to a Basic Income is that the minimum wage could be smaller than it might otherwise be. For example if the minimum wage was decreased by the same amount that the Basic Income provided then the minimum income would remain the same while employers would pay less, this would affect the viability of certain types of contract work web sites if they were subject to minimum wage laws (currently they just ignore the minimum wage laws by paying based on job completion instead of hours worked). I don t think that the minimum wage should decrease that much though, currently employers are able to run viable businesses with the minimum wage laws and I don t think that a Basic Income should be used as a way of helping corporations avoid paying their employees. If we had a Basic Income then there s many ways that it could be used to stabilise the economy. If people could pay their rent even if they lost their job then a down-turn in one area of the economy wouldn t immediately affect other areas. Also if rent payments were deducted automatically from an account used to receive the Basic Income then landlords would be more likely to rent to poor people as they could be guaranteed to receive rent payments (it would be easy to have a contractual agreement for rent to take priority and have bank computers enforce that). The Implementation Problem I don t think that my idea would have any significant negative effects. It wouldn t decrease government revenues if tax was adjusted accordingly. It wouldn t make people stop working as people who don t want to work already avoid it. It would help people who are out of work to get work by reducing the barriers to entry in terms of paperwork and of unreasonable cuts to Newstart making it bad value to take part time work. I think that the big problem with implementing it is people who want to prevent poor people from having opportunities. They want to reduce social security and minimum wages even though such changes will in the long run only give less tax revenue and greater expense in law enforcement. It seems rather ironic that such hostility often comes from people at the low end of the middle class whos jobs are most likely to be at risk from new technology. As on-going technological development reduces the number of workers that are required to keep things running we need to have some form of payment to the people who aren t doing enough work to survive. A decent Basic Income is a much better option than giving Newstart payments and forcing a significant portion of the population into a degrading search for jobs that don t exist. As that s the inevitable future I think we should make political changes to deal with it sooner rather than later. However a Basic Income might be implemented now it s surely going to be a lot better than what might happen if we wait until the majority of the population are unemployed before doing something about it.

• [1] http://tinyurl.com/mwemen5
  
• [2] http://www.humanservices.gov.au/customer/services/centrelink/newstart-allowance
• [3] http://www.fairwork.gov.au/PAY/NATIONAL-MINIMUM-WAGE/pages/default.aspx
• [4] http://tinyurl.com/mjq3dwl

It has been a while since I managed to publish the last interview, but the Debian Edu / Skolelinux community is still going strong, and yesterday we even had a new school administrator show up on #debian-edu to share his success story with installing Debian Edu at their school. This time I have been able to get some helpful comments from the creator of Knoppix, Klaus Knopper, who was involved in a Skolelinux project in Germany a few years ago. Who are you, and how do you spend your days? I am Klaus Knopper. I have a master degree in electrical engineering, and is currently professor in information management at the university of applied sciences Kaiserslautern / Germany and freelance Open Source software developer and consultant. All of this is pretty much of the work I spend my days with. Apart from teaching, I'm also conducting some more or less experimental projects like the Knoppix GNU/Linux live system (Debian-based like Skolelinux), ADRIANE (a blind-friendly talking desktop system) and LINBO (Linux-based network boot console, a fast remote install and repair system supporting various operating systems). How did you get in contact with the Skolelinux / Debian Edu project? The credit for this have to go to Kurt Gramlich, who is the German coordinator for Skolelinux. We were looking for an all-in-one open source community-supported distribution for schools, and Kurt introduced us to Skolelinux for this purpose. What do you see as the advantages of Skolelinux / Debian Edu?

• Quick installation,
• works (almost) out of the box,
• contains many useful software packages for teaching and learning,
• is a purely community-based distro and not controlled by a single company,
• has a large number of supporters and teachers who share their experience and problem solutions.

What do you see as the disadvantages of Skolelinux / Debian Edu?

• Skolelinux is - as we had to learn - not easily upgradable to the next version. Opposed to its genuine Debian base, upgrading to a new version means a full new installation from scratch to get it working again reliably.
• Skolelinux is based on Debian/stable, and therefore always a little outdated in terms of program versions compared to Edubuntu or similar educational Linux distros, which rather use Debian/testing as their base.
• Skolelinux has some very self-opinionated and stubborn default configuration which in my opinion adds unnecessary complexity and is not always suitable for a schools needs, the preset network configuration is actually a core definition feature of Skolelinux and not easy to change, so schools sometimes have to change their network configuration to make it "Skolelinux-compatible".
• Some proposed extensions, which were made available as contribution, like secure examination mode and lecture material distribution and collection, were not accepted into the mainline Skolelinux development and are now not easy to maintain in the future because of Skolelinux somewhat undeterministic update schemes.
• Skolelinux has only a very tiny number of base developers compared to Debian.

For these reasons and experience from our project, I would now rather consider using plain Debian for schools next time, until Skolelinux is more closely integrated into Debian and becomes upgradeable without reinstallation. Which free software do you use daily? GNU/Linux with LXDE desktop, bash for interactive dialog and programming, texlive for documentation and correspondence, occasionally LibreOffice for document format conversion. Various programming languages for teaching. Which strategy do you believe is the right one to use to get schools to use free software? Strong arguments are

• Knowledge is free, and so should be methods and tools for teaching and learning.
• Students can learn with and use the same software at school, at home, and at their working place without running into license or conversion problems.
• Closed source or proprietary software hides knowledge rather than exposing it, and proprietary software vendors try to bind customers to certain products. But teachers need to teach science, not products.
• If you have everything you for daily work as open source, what would you need proprietary software for?

This Monday, I attended a workshop on Multi-party Off the Record Messaging and Deniability hosted by the Calyx Institute. The discussion was a combination of legal and technical people, looking at how the characteristics of this particular technology affect (or do not affect) the law. This is a report-back, since I know other people wanted to attend. I'm not a lawyer, but I develop software to improve communications security, I care about these questions, and I want other people to be aware of the discussion. I hope I did not misrepresent anything below. I'd be happy if anyone wants to offer corrections. BackgroundOff the Record Messaging (OTR) is a way to secure instant messaging (e.g. jabber/XMPP, gChat, AIM). The two most common characteristics people want from a secure instant messaging program are:

Authentication

Each participant should be able to know specifically who the other parties are on the chat.

Confidentiality

The content of the messages should only be intelligible to the parties involved with the chat; it should appear opaque or encrypted to anyone else listening in. Note that confidentiality effectively depends on authentication -- if you don't know who you're talking to, you can't make sensible assertions about confidentiality.

As with many other modern networked encryption schemes, OTR relies on each user maintaining a long-lived "secret key", and publishing a corresponding "public key" for their peers to examine. These keys are critical for providing authentication (and by extension, for confidentiality). But OTR offers several interesting characteristics beyond the common two. Its most commonly cited characteristics are "forward secrecy" and "deniability".

Forward secrecy

Assuming the parties communicating are operating in good faith, forward secrecy offers protection against a special kind of adversary: one who logs the encrypted chat, and subsequently steals either party's long-term secret key. Without forward secrecy, such an adversary would be able to discover the content of the messages, violating the confidentiality characteristic. With forward secrecy, this adversary is be stymied and the messages remain confidential.

Deniability

Deniability only comes into play when one of the parties is no longer operating in good faith (e.g. their computer is compromised, or they are collaborating with an adversary). In this context, if Alice is chatting with Bob, she does not want Bob to be able to cryptographically prove to anyone else that she made any of the specific statements in the conversation. This is the focus of Monday's discussion. To be clear, this kind of deniability means Alice can correctly say "you have no cryptographic proof I said X", but it does not let her assert "here is cryptographic proof that I did not say X" (I can't think of any protocol that offers the latter assertion). The opposite of deniability is a cryptographic proof of origin, which usually runs something like "only someone with access to Alice's secret key could have said X."

The traditional two-party OTR protocol has offered both forward secrecy and deniability for years. But deniability in particular is a challenging characteristic to provide for group chat which is the domain of Multi-Party OTR (mpOTR). You can read some past discussion about the challenges of deniability in mpOTR (and why it's harder when there are more than two people chatting) from the otr-users mailing list. If you're not doing anything wrong... The discussion was well-anchored by a comment from another participant who cheekily asked "If you're not doing anything wrong, why do you need to hide your chat at all, let alone be able to deny it?" The general sense of the room was that we'd all heard this question many times, from many people. There are lots of problems with the ideas behind the question from many perspectives. But just from a legal perspective, there are at least two problems with the way this question is posed:

• laws themselves are not always just (e.g. consider chat communications between an interracial couple in the USA before 1967, if instant messaging had existed at the time), and
• law enforcement (or a legal adversary in civil litigation) may have a different understanding or interpretation of the law than you do (e.g. consider chat communications between a corporate or government whistleblower and a journalist).

In these situations, people confront real risk from the law. If we care about these people, we need to figure out if we can build systems to help them reduce that legal risk (of course we also need to fix broken laws, and the legal environment in general, but those approaches were out of scope for this discussion). The Legal Utility of Deniability Monday's meeting was called specifically because it wasn't clear how much real-world usefulness there is in the "deniability" characteristic, and whether this feature is worth the development effort and implementation tradeoffs required. In particular, the group was interested in deniability's utility in legal contexts; many (most?) people in the room were lawyers, and it's also not clear that deniability has much utility outside of a formal legal setting. If your adversary isn't constrained by some rule of law, they probably won't care at all whether there is a cryptographic proof or not that you wrote a particular message (In retrospect, one possible exception is exposure in the media, but we did not discuss that scenario). Places of possible usefulness So where might deniability come in handy during civil litigation or a criminal trial? Presumably the circumstance is that a piece of a chat log is offered as incriminating evidence, and the defendant is trying to deny something that they appear to have said in the log. This denial could take place in two rather different contexts: during rules over admissibility of evidence, or (once admitted) in front of a jury. In legal wrangling over admissibility, apparently a lot of horse-trading can go on -- each side concedes some things in exchange for the other side conceding other things. It appears that cryptographic proof of origin (that is, a lack of deniability) on the chat logs themselves might reduce the amount of leverage a defense lawyer can get from conceding or arguing strongly over that piece of evidence. For example, if the chain of custody of a chat transcript is fuzzy (i.e. the transcript could have been mishandled or modified somehow before reaching trial), then a cryptographic proof of origin would make it much harder for the defense to contest the chat transcript on the grounds of tampering. Deniability would give the defense more bargaining power. In arguing about already-admitted evidence before a jury, deniability in this sense seems like a job for expert witnesses, who would need to convince the jury of their interpretation of the data. There was a lot of skepticism in the room over this, both around the possibility of most jurors really understanding what OTR's claim of deniability actually means, and on jurors' ability to distinguish this argument from a bogus argument presented by an opposing expert witness who is willing to lie about the nature of the protocol (or who misunderstands it and passes on their misunderstanding to the jury). The complexity of the tech systems involved in a data-heavy prosecution or civil litigation are themselves opportunities for lawyers to argue (and experts to weigh in) on the general reliability of these systems. Sifting through the quantities of data available and ensuring that the appropriate evidence is actually findable, relevant, and suitably preserved for the jury's inspection is a hard and complicated job, with room for error. OTR's deniability might be one more element in a multi-pronged attack on these data systems. These are the most compelling arguments for the legal utility of deniability that I took away from the discussion. I confess that they don't seem particularly strong to me, though some level of "avoiding a weaker position when horse-trading" resonates with me. What about the arguments against its utility? Limitations The most basic argument against OTR's deniability is that courts don't care about cryptographic proof for digital evidence. People are convicted or lose civil cases based on unsigned electronic communications (e.g. normal e-mail, plain chat logs) all the time. OTR's deniability doesn't provide any legal cover stronger than trying to claim you didn't write a given e-mail that appears to have originated from your account. As someone who understands the forgeability of e-mail, i find this overall situation troubling, but it seems to be where we are. Worse, OTR's deniability doesn't cover whether you had a conversation, just what you said in that conversation. That is, Bob can still cryptographically prove to an adversary (or before a judge or jury) that he had a communication with someone controlling Alice's secret key (which is probably Alice); he just can't prove that Alice herself said any particular part of the conversation he produces. Additionally, there are runtime tradeoffs depending on how the protocol manages to achieve these features. For example, forward secrecy itself requires an additional round trip or two when compared to authenticated, encrypted communications without forward secrecy (a "round trip" is a message from Alice to Bob followed by a message back from Bob to Alice). Getting proper deniability into the mpOTR spec might incur extra latency (imagine having to wait 60 seconds after everyone joins before starting a group chat, or a pause in the chat of 15 seconds when a new member joins) or extra computational power (meaning that they might not work well on slower/older devices) or an order of magnitude more bandwidth (meaning that chat might not work at all on a weak connection). There could also simply be complexity that makes it harder to correctly implement a protocol with deniability than an alternate protocol without deniability. Incorrectly-implemented software can put its users at risk. I don't know enough about the current state of mpOTR to know what the specific tradeoffs are for the deniability feature, but it's clear there will be some. Who decides whether the tradeoffs are worth the feature? Other kinds of deniability Further weakening the case for the legal utility of OTR's deniability, there seem to be other ways to get deniability in a legal context over a chat transcript. There are deniability arguments that can be made from outside the protocol. For example, you can always claim someone else took control of your computer while you were asleep or using the bathroom or eating dinner, or you can claim that your computer had a virus that exported your secret key and it must have been used by someone else. If you're desperate enough to sacrifice your digital identity, you could arrange to have your secret key published, at which point anyone can make signed statements with it. Having forward secrecy makes it possible to expose your secret key without exposing the content of your past communications to any listener who happened to log them. Conclusion My takeaway from the discussion is that the legal utility of OTR's deniability is non-zero, but quite low; and that development energy focused on deniability is probably only justified if there are very few costs associated with it. Several folks pointed out that most communications-security tools are too complicated or inconvenient to use for normal people. If we have limited development energy to spend on securing instant messaging, usability and ubiquity would be a better focus than this form of deniability. Secure chat systems that take too long to make, that are too complex, or that are too cumbersome are not going to be adopted. But this doesn't mean people won't chat at all -- they'll just use cleartext chat, or maybe they'll use supposedly "secure" protocols with even worse properties: for example, without proper end-to-end authentication (permitting spoofing or impersonation by the server operator or potentially by anyone else); with encryption that is reversible by the chatroom operator or flawed enough to be reversed by any listener with a powerful computer; without forward secrecy; or so on. As a demonstration of this, we heard some lawyers in the room admit to using Skype to talk with their clients even though they know it's not a safe communications channel because their clients' adversaries might have access to the skype messaging system itself. My conclusion from the meeting is that there are a few particular situations where deniability could be useful legally, but that overall, it is not where we as a community should be spending our development energy. Perhaps in some future world where all communications are already authenticated, encrypted, and forward-secret by default, we can look into improving our protocols to provide this characteristic, but for now, we really need to work on usability, popularization, and wide deployment. Thanks Many thanks to Nick Merrill for organizing the discussion, to Shayana Kadidal and Stanley Cohen for providing a wealth of legal insight and legal experience, to Tom Ritter for an excellent presentation of the technical details, and to everyone in the group who participated in the interesting and lively discussion. Tags: chat, deniability, otr, security

My laptop is just over 3 years old, which is about the point I start to think about a replacement. At present there's nothing that's an obvious contender so I've been looking at an SSD to prolong it by another year or two. One of the other thoughts I had is that I currently use dm-crypt under Linux to provide whole disk encryption for everything except the boot partition - I have a bunch of my personal financial and immigration documents stored that I'd prefer not to get disclosed if my laptop is stolen. Modern drives have started offered integral AES encryption options, so perhaps I could offload that to the drive (my i5 470UM lacks the hardware instructions for this). General consensus in the pub (where all the best security advice is to be found) is that no one present trusted SSD firmware authors to not use some badly chosen AES crypto mode, or leave the key lying around plain text in easily readable flash, or some other implementation mishap. So how hard would it be to retrofit reliable (or at least source verifiable and thus more reliable) crypto to an SSD? There was an impressive article recently about reverse engineering the firmware of a HDD, to the point of modifying data returned to the host and also running Linux on the controller. It seems that SSD firmware should be easier - NAND is simpler to talk to than motors and magnetic sensors, right? It's a case of gluing together a SATA interface, a NAND controller and an AES offload engine, yes? Aside from the minor matter of finding a suitable drive with an available JTAG interface, a controller with docs (or more likely that can be reverse engineered) and enough time to produce a replacement open firmware, that is. Alternatively can anyone provide some idea of how secure the available laptop SSDs on the market actually are? I'm fine with "the NSA can read your data if they want" because a determined attacker will be able to find other ways to get my data anyway, but I don't want "anyone who finds the drive can use this loophole in the firmware by wiggling some bits with jtag to dump the key and read all your data".

(Discussion of a presentation I gave at Kiwicon last month)

Kexec is a Linux kernel feature intended to allow the booting of a replacement kernel at runtime. There's a few reasons you might want to do that, such as using Linux as a bootloader[1], rebooting without having to wait for the firmware to reinitialise or booting into a minimal kernel and userspace that can be booted on crash in order to save system state for later analysis.

But kexec's significantly more flexible than this. The kexec system call interface takes a list of segments (ie, pointers to a userspace buffer and the desired target destination) and an entry point. The kernel relocates those segments and jumps to the entry point. That entry point is typically code referred to as purgatory, due to the fact that it lives between the world of the first kernel and the world of the second kernel. The purgatory code sets up the environment for the second kernel and then jumps to it. The first kernel doesn't need to know anything about what the second kernel is or does. While it's conventional to load Linux, you can load just about anything.

The most important thing to note here is that none of this is signed. In other words, despite us having a robust in-kernel mechanism for ensuring that only signed modules can be inserted into the kernel, root can still load arbitrary code via kexec and execute it. This seems like a somewhat irritating way to patch the running kernel, so thankfully there's a much more straightforward approach.

I modified kexec to add an additional loader and uploaded the code here. Build and install it. Make sure that /sys/module/module/parameters/sig_enforce on your system is "Y". Then, as root, do something like:
kexec --type="dummy" --address= printf "0x%x" $(( $(grep "B sig_enforce" /proc/kallsyms awk ' print "0x"$1 ') & 0x7fffffff)) --value=0 --load-preserve-context --mem-max=0x10000 /bin/true
to load it[2]. Now do kexec -e and watch colours flash and check /sys/module/module/parameters/sig_enforce again.

The beauty of this approach is that it doesn't rely on any kernel bugs - it's using kernel functionality that was explicitly designed to let you do this kind of thing (ie, run arbitrary code in ring 0). There's not really any way to fix it beyond adding a new system call that has rather tighter restrictions on the binaries that can be loaded. If you're using signed modules but still permit kexec, you're not really adding any additional security.

But that's not the most interesting way to use kexec. If you can load arbitrary code into the kernel, you can load anything. Including, say, the Windows kernel. ReactOS provides a bootloader that's able to boot the Windows 2003 kernel, and it shouldn't be too difficult for a sufficiently enterprising individual to work out how to get Windows 8 booting. Things are a little trickier on UEFI - you need to tell the firmware which virtual physical map to use, and you can only do it once. If Linux has already done that, it's going to be difficult to set up a different map for Windows. Thankfully, there's an easy workaround. Just boot with the "noefi" kernel argument and the kernel will skip UEFI setup, letting you set up your own map.

Why would you want to do this? The most obvious reason is avoiding Secure Boot restrictions. Secure Boot, if enabled, is explicitly designed to stop you booting modified kernels unless you've added your own keys. But if you boot a signed Linux distribution with kexec enabled (like, say, Ubuntu) then you're able to boot a modified Windows kernel that will still believe it was booted securely. That means you can disable stuff like the Early Launch Anti-Malware feature or driver signing, or just stick whatever code you want directly into the kernel. In most cases all you'd need for this would be a bootloader, kernel and an initrd containing support for the main storage, an ntfs driver and a copy of kexec-tools. That should be well under 10MB, so it'll easily fit on the EFI system partition. Copy it over the Windows bootloader and you should be able to boot a modified Windows kernel without any terribly obvious graphical glitches in the process.

And that's the story of why kexec is disabled on Fedora when Secure Boot is enabled.

[1] That way you only have to write most drivers once
[2] The address section finds the address of the sig_enforce symbol in the kernel, and the value argument tells the dummy code what value to set that address to. --load-preserve-context informs the kernel that it should save hardware state in order to permit returning to the original kernel. --mem-max indicates the highest address that the kernel needs to back up. /bin/true is just there to satisfy the argument parser.

comments

So, using the command:

root@new# ssh root@old dd if=/dev/vg/somedisk dd of=/dev/vg/somedisk

appears to fail, getting a SIGTERM at some point for no discernable reason... however, using

root@old# dd if=/dev/vg/somedisk ssh root@new dd of=/dev/vg/somedisk

works fine. The pull version fails at a fairly random point after a fairly undefined period of time. The push version works everytime. This is most confusing and odd... Dear lazyweb, please give me some new ideas as to what's going on, it's driving me nuts! Update: solved... A different daemon wasn't limiting it's killing habits in the case that a certain process wasn't running, and was killing the ssh process on the new server almost at random, found the bug in the code and now testing with that. Thanks for all the suggestions though, much appreciated.

I ve just read Bartleby the Scrivener which is a short story about a scrivener who refused to work saying I d prefer not to . It reminded me of some situations in the computer industry. I ve never seen a single case where someone preferred not to work when everyone around them (colleagues and management) wanted them to work. But then the incidence of having an entire team and management wanting to work efficiently isn t nearly as common as one might imagine. In some cases it s desired that someone not work, such as a former colleague who was hired as a sysadmin but did nothing but change backup tapes (a few hours work per week). Not having him login as root improved the general reliability of the servers but it was fortunate that we never needed to restore from backups One time I had a colleague who preferred to spend most of his time in the office searching the Internet for videos of street fights. I have often told colleagues that I would prefer them to work, but in the case of a guy who s only hobby is street-fighting I decided to let it go. Managing people can be difficult, particularly for someone who doesn t like disagreements. Some managers that I ve reported to seemed to prefer not to manage in an apparent attempt to avoid disputes. One time when I complained about a colleague not even having a suitable computer to permit doing any work a manager responded with the rhetorical question what do you expect me to do? . That manager didn t do any annual reviews of staff for over a year, he only eventually did some reviews because he was told that his scheduled promotion was on hold until he got them done. I got the impression that at least two levels of management preferred not to work at that company. Sometimes it just gets weird though, such as the occasion when I was the only member of a team and the manager who was supposedly managing no-one but me never seemed to have time to have a meeting with me. But he didn t want me to bypass him and talk directly to other people in the company, so he preferred not to work and not to have anyone else do his job. Most of the companies that I ve worked for in a full-time capacity didn t seem to have any effective technical interviews (note that I ve mostly worked for financial companies and ISPs not free software companies). So it seems that anyone with minimal computer skills who wants a well paying job could just send out a CV to a bunch of recruiting agencies, get interviewed by enough companies to eventually hit one without a technical interview process and then find a job that doesn t require work. Depression The Wikipedia page about Bartleby the Scrivener [2] suggests that Bartleby was depressed. I wonder how much of the lack of performance I ve witnessed has been due to depression. There appears to be a strong correlation between work environments that cause depression and people preferring not to work. Maybe managers should be considering how to make work less depressing to try and get more effective employees (in terms of quality and quantity of work). One example of this is the sysadmin team death spiral I ve witnessed where no-one can automate solving problems (EG by cron jobs to manage resource usage and analysis tools to find minor problems before they become major problems) because everyone is dedicated to fixing things that break needlessly (EG systems crashing due to lack of disk space). When people start getting control over recurring problems and automating things then the work becomes increasingly about solving problems and less about implementing the same manual processes every day/week and it s more fun and effective for everyone. At the BoF on depression at LCA 2013 one delegate stated that many companies have people in HR who can arrange support for depressed employees. Apparently if you are depressed and you work for a company that s large enough to have a HR department then it can be beneficial to talk to HR about it. That probably works well in the case where an employee is depressed but the company is working well. But in the case where the company isn t working well it seems unlikely to help. David Graeber wrote an interesting article about Bullshit Jobs [3]. He goes a bit far, I don t think that late night pizza delivery is a bullshit job and actuaries are useful to society. But his points about the existence of useless jobs are reasonable. Management Levels I sometimes wonder whether there is some benefit in establishing social norms about working and then having management take little interest in how it happens. If a team works well together then management could just set deadlines (which would be negotiated with employees who know what s possible) and let the team work out how to do it. Then instead of having one manager for each team of ~10 people who theoretically tracks what everyone is doing you could have one manager for a dozen teams who just tracks overall team performance essentially remove a layer of management. Valve is famous for having no formal management structure and for getting things done, unfortunately that apparently allows school-style cliques to block actions [4]. But I think that the Valve experiment is useful and provides some ideas that can be used by other companies. Maybe if instead of requiring consensus of the entire company for hiring decisions they only required consensus of the team things would have worked better. Of course another down-side to such things is that hierarchical management can be good for avoiding discrimination and bullying. The article I cited about Valve compares it to high-school. It could be that Valve employees were all nice people who only hired other nice people. But if similar systems were implemented in many companies then some would surely end up being like a typical high school with all the bullying and mistreatment of minority groups that entails. Michael O. Church wrote an interesting article in which he divides employees into four categories, loser , clueless , psychopaths , and technocrats (note that he didn t invent the first three names) [5]. In his model the clueless category includes most middle-management. I think that there are some problems with Michael s model and I m not arguing for a technocracy (which is how this post might be interpreted in terms of his ideas). But I think he demonstrates some of the real problems in the way companies are managed and in his model the losers prefer not to work as long as they can get paid. Conclusion I don t have any good solutions to these problems to offer. It seems that the best we can hope for is incremental change to make work less depressing, to have the minimal amount of management, and to avoid bullshit jobs .

• [1] http://www.gutenberg.org/ebooks/11231
• [2] http://en.wikipedia.org/wiki/Bartleby,_the_Scrivener
• [3] http://www.strikemag.org/bullshit-jobs/
• [4] http://www.wired.com/gamelife/2013/07/wireduk-valve-jeri-ellsworth/
• [5] http://tinyurl.com/kxcduch

While I remember, I have uploaded the slides from my talk about Solr and Perl at the London Perl Workshop. This talk was inspired by having seen and contributed to at least five different sets of Solr search code at my current job, all of which (I now believe) were doing it wrong. I distilled this hard-won knowledge into a 20 minute talk, which - funny story - I actually delivered twice to work around a cock-up in the printed schedule. I don't believe any video was successfully taken, but I may be proved wrong later. I have also uploaded the Parse::Yapp grammar mentioned in the talk. In case you don't have time to read the slides, the right way to present Solr via Perl is to use the 'edismax' parser, and write your code a bit like this:

my $solr = WebService::Solr->new($url);
my $s = $query->param('q');
# WebService::Solr::Query objects are useful for
# 'fq' params, but avoid them for main 'q' param.
my $options =  
 fq => [WebService::Solr::Query->new(...)];
 ;
$solr->search($s, \%options);

The key thing here is not to put any complicated parsing code in between the user and Solr. Avoid Search::QueryParser at all costs.

Backups are fun and exciting! Restores are exciting, in a terrifying and stressful way. Fixing serious bugs is gratifying, in a depressing way. I am glad to announce two software releases: Obnam version 1.6.1 and larch version 1.20131130. Obnam is my backup application, larch is a Python copy-on-write B-tree implementation that Obnam uses. I've uploaded the new versions to Debian unstable and to my own apt repository at [code.liw.fi] (also for wheezy). (I don't have the energy to upload to Debian backports: help is welcome there.) These are mainly bug fix releases, and minor improvements. The larch release fixes serious problems, and everyone should be upgrading. NEWS for larch:

• Serious bug fixed: the "KeyError" crash for reference counts. This was false memory use optimisation, which triggered a rare bug in related code. Repeatable test case by Rob Kendrick, and helpful analysis by Itamar Turing-Trauring.
• Serious bug fixed: another "node missing" bug. This crash was caused by a bug that overwrote on-disk reference count groups with zeroes. Repeatable test case by Rob Kendrick.
• Fixes to fsck from Antoine Brenner.

NEWS for Obnam (combining versions 1.6 and 1.6.1, both released today):

• Fix Debian package dependencies correctly.
• Stop logging paramiko exceptions that get converted into another type of exception by the SFTP plugin in Obnam.
• obnam-benchmark can now use an installed version of larch. Patch by Lars Kruse.
• Obnam has been ported to FreeBSD by Itamar Turner-Trauring of HybridCluster.
• Backup progress reporting now reports scanned file data, not just backed up file data. This will hopefully be less confusing to people.
• The list-keys, client-keys, and list-toplevels commands now obey a new option, --key-details, to show the usernames attached to each public key. Patch by Lars Kruse.
• New option --ssh-command to set the command Obnam runs when invoking ssh. patch by Lars Kruse.
• obnam clients can now be used without being an existing client. Patch by Itamar Turner-Trauring.
• New option --ssh-host-keys-check to better specify how SSH host keys should be checked. Patch by Itamar Turner-Trauring.

Bug fixes:

• Fix"obnam list-toplevels so it doesn't give an error when it's unable to read the per-client directory of another client, when encryption is used. Fix by Lars Kruse.
• Fix the encryption plugin to give a better error message when it looks for client directories but fails to find them. Fix by Lars Kruse.
• obnam list-toplevels got confused when the repository contained extra files, such as "lock" (left there by a previous, crashed Obnam run). It no longer does. Fix by Lars Kruse.
• The SFTP plugin now handles another error code (EACCESS) when writing a file and the directory it should go into not existing. Patch by Armin Gr linger.
• Obnam's manual page now explains about breaking long logical lines into multiple physical ones.
• The /~/ path prefix in SFTP URLs works again, at least with sufficiently new versions of Paramiko (1.7.7.1 in Debian wheezy is OK). Reported by Lars Kruse.
• The Nagios plugin to report errors in a way Nagios expects. Patch by Martijn Grendelman.
• The Nagios plugin for Obnam now correctly handles the case where a backup repository for a client exists, but does not have a backup yet. Patch by Lars Kruse.
• obnam ls now handles trailing slashes in filename arguments. Reported by Biltong.
• When restoring a backup, Obnam will now continue past errors, instead of aborting with the first one. Patch by Itamar Turner-Trauring.

Following up on my port of the crystalhd plugin to the gstreamer 1.0 api I realized that the CrystalHD repo is pretty dormant. After reading slomo's nice article about GStreamer and hardware integration and a short off list mail exchange I decided to split the GStreamer part out of the CrystalHD repo and to try to get the plugin into gst-plugins-bad. Since the kernel part is already in linux kernel's staging area there would not be much left in the repo except for the libcrystalhd library itself and the firmware blobs. So I split them out as well and started to clean them up a bit by moving it to autoconf/automake, dropping the need for a C++ compiler and adding symbol versioning among other things. So up to know video is still smooth with:

gst-launch-1.0 filesrc location=sample.mp4 ! decodebin ! xvimagesink

after jhbuilding up to gst-plugins-bad. There are #ifdefs for macosx and windows but I doubt they're functional but in case anybody is building libcrystalhd on these these platforms it'd be great to know if it still works. Should these efforts lead to the crystalhd plugin being merged into GStreamer getting the kernel driver out of staging would be a great next step. This blog is flattr enabled.

Appointed to the Debian Tech Committee I m pleased to announce that I ve been appointed to serve on the Debain Technical Committee. I d like to thank the other committee members and the Debian project leader, Lucas Nussbaum, for giving me this opportunity to serve. I look forward to working within the committee to further Debian s goals as the universal operating system.

This is one thing I have wanted to do for a long time: configure Mutt to encrypt all messages sent to addresses for which I have a valid public key. Well, here is an awk-based script to generate that configuration. (Yes, I know, a similar script was already written. But I did not see it at first, and I find mine more readable. :-) )Code

#! /bin/sh
set -e
# Specific hooks set global configuration values for Mutt, which are not
# reset for new messages, so a default hook is needed to set the default
# value (do not try encrypting all messages).
printf "send-hook . unset crypt_autoencrypt\n\n"
cat <<EOF
# This group contains all known PGP users, and can be used to define
# hooks, for instance to encrypt all messages sent to PGP users, or to
# add a specific signature to promote PGP usage to non-PGP users.
EOF
# Generate a machine-readable list of known keys
gpg2 --batch --with-colons --list-keys \
      awk -- '
        BEGIN  
            FS = ":"
            # A flag that indicates whether or not we are in a public
            # key with usable encryption capability
            usable = 0
         
        # Detect beginning of public keys with usable encryption
        # capability
        $1 == "pub" && $12 ~ /E/   usable = 1  
        # Detect beginning of public keys without usable encryption
        # capability
        $1 == "pub" && $12 !~ /E/   usable = 0  
        
        # Only consider user IDs from public keys with usable encryption
        # capability and with regular, marginal, full or ultimate
        # validity (n, m, f or u in the second field)
        usable && $1 == "uid" && $2 ~ /[nmfu]/ && $10 ~ /@/  
            # Remove everything before and after the email address in
            # brackets
            sub(/^[^<]*</, "", $10)
            sub(/>[^>]*$/, "", $10)
            # Finally print the email address
            print $10
         ' \
      sort -u \
       
        # Group addresses by ten to reduce the number of Mutt commands
        finished=0
        while [ $finished -ne 1 ]
        do
            addresses=""
            for i in 0 1 2 3 4 5 6 7 8 9
            do
                if read address
                then
                    addresses="$addresses $address"
                else
                    finished=1
                    break
                fi
            done
            # Add PGP users' addresses to a pgp-users group
            printf "group -group pgp-users -addr %s\n" \
                "$addresses"
        done
     
# Build a hook to try encrypting messages sent to PGP users
printf "\n# Encrypt all messages sent to known PGP users\n"
printf "send-hook \"%%C pgp-users\" set crypt_autoencrypt\n" \
printf "\n# Add a specific signature to promote PGP usage to non-PGP users\n"
printf "#send-hook \"!%%C pgp-users\" set signature=~/.signature.use-pgp\n"

Usage Script usage This script generates uses GnuPG to print a list of all known keys, takes only valid ones, and uses them to build a series of configuration instructions for Mutt, that define hooks that are triggered when you write a message to them. This configuration has to be written to your Mutt configuration file:

$ bin/gen-pgp-hooks.sh >> ~/.muttrc

Or better (far better, in fact), to a dedicated configuration file you will refer to in your main one:

$ bin/gen-pgp-hooks.sh > ~/.muttrc.crypt-recipients
$ echo "source ~/.muttrc.crypt-recipients" >> ~/.muttrc

You may want to adapt this script to it directly writes to that file rather than having to redirect it. Also, remember to run it when you refresh your public keyring or add new keys to it. Mutt usage These hooks will make Mutt try to encrypt all messages you send to at least one known PGP user. That means it will try it even for messages you send to a PGP user and to non-PGP ones. In these cases, it will not find keys for all the recipient, and ask you which key to use; as you have none, you will have to quit that prompt by typing ^G, and manually disable encryption by accessing the PGP options menu with the key p.