Review: Unseen Academicals, by Terry Pratchett

Series:	Discworld #37
Publisher:	Harper
Copyright:	October 2009
Printing:	November 2014
ISBN:	0-06-233500-6
Format:	Mass market
Pages:	517

Unseen Academicals is the 37th Discworld novel and includes many of the long-standing Ankh-Morpork cast, but mostly as supporting characters. The main characters are a new (and delightful) bunch with their own concerns. You arguably could start reading here if you really wanted to, although you would risk spoiling several previous books (most notably Thud!) and will miss some references that depend on familiarity with the cast. The Unseen University is, like most institutions of its sort, funded by an endowment that allows the wizards to focus on the pure life of the mind (or the stomach). Much to their dismay, they have just discovered that an endowment that amounts to most of their food budget requires that they field a football team. Glenda runs the night kitchen at the Unseen University. Given the deep and abiding love that wizards have for food, there is both a main kitchen and a night kitchen. The main kitchen is more prestigious, but the night kitchen is responsible for making pies, something that Glenda is quietly but exceptionally good at. Juliet is Glenda's new employee. She is exceptionally beautiful, not very bright, and a working class girl of the Ankh-Morpork streets down to her bones. Trevor Likely is a candle dribbler, responsible for assisting the Candle Knave in refreshing the endless university candles and ensuring that their wax is properly dribbled, although he pushes most of that work off onto the infallibly polite and oddly intelligent Mr. Nutt. Glenda, Trev, and Juliet are the sort of people who populate the great city of Ankh-Morpork. While the people everyone has heard of have political crises, adventures, and book plots, they keep institutions like the Unseen University running. They read romance novels, go to the football games, and nurse long-standing rivalries. They do not expect the high mucky-mucks to enter their world, let alone mess with their game. I approached Unseen Academicals with trepidation because I normally don't get along as well with the Discworld wizard books. I need not have worried; Pratchett realized that the wizards would work better as supporting characters and instead turns the main plot (or at least most of it; more on that later) over to the servants. This was a brilliant decision. The setup of this book is some of the best of Discworld up to this point. Trev is a streetwise rogue with an uncanny knack for kicking around a can that he developed after being forbidden to play football by his dear old mum. He falls for Juliet even though their families support different football teams, so you may think that a Romeo and Juliet spoof is coming. There are a few gestures of one, but Pratchett deftly avoids the pitfalls and predictability and instead makes Juliet one of the best characters in the book by playing directly against type. She is one of the characters that Pratchett is so astonishingly good at, the ones that are so thoroughly themselves that they transcend the stories they're put into. The heart of this book, though, is Glenda.

Glenda enjoyed her job. She didn't have a career; they were for people who could not hold down jobs.

She is the kind of person who knows where she fits in the world and likes what she does and is happy to stay there until she decides something isn't right, and then she changes the world through the power of common sense morality, righteous indignation, and sheer stubborn persistence. Discworld is full of complex and subtle characters fencing with each other, but there are few things I have enjoyed more than Glenda being a determinedly good person. Vetinari of course recognizes and respects (and uses) that inner core immediately. Unfortunately, as great as the setup and characters are, Unseen Academicals falls apart a bit at the end. I was eagerly reading the story, wondering what Pratchett was going to weave out of the stories of these individuals, and then it partly turned into yet another wizard book. Pratchett pulled another of his deus ex machina tricks for the climax in a way that I found unsatisfying and contrary to the tone of the rest of the story, and while the characters do get reasonable endings, it lacked the oomph I was hoping for. Rincewind is as determinedly one-note as ever, the wizards do all the standard wizard things, and the plot just isn't that interesting. I liked Mr. Nutt a great deal in the first part of the book, and I wish he could have kept that edge of enigmatic competence and unflappableness. Pratchett wanted to tell a different story that involved more angst and self-doubt, and while I appreciate that story, I found it less engaging and a bit more melodramatic than I was hoping for. Mr. Nutt's reactions in the last half of the book were believable and fit his background, but that was part of the problem: he slotted back into an archetype that I thought Pratchett was going to twist and upend. Mr. Nutt does, at least, get a fantastic closing line, and as usual there are a lot of great asides and quotes along the way, including possibly the sharpest and most biting Vetinari speech of the entire series.

The Patrician took a sip of his beer. "I have told this to few people, gentlemen, and I suspect never will again, but one day when I was a young boy on holiday in Uberwald I was walking along the bank of a stream when I saw a mother otter with her cubs. A very endearing sight, I'm sure you will agree, and even as I watched, the mother otter dived into the water and came up with a plump salmon, which she subdued and dragged on to a half-submerged log. As she ate it, while of course it was still alive, the body split and I remember to this day the sweet pinkness of its roes as they spilled out, much to the delight of the baby otters who scrambled over themselves to feed on the delicacy. One of nature's wonders, gentlemen: mother and children dining on mother and children. And that's when I first learned about evil. It is built into the very nature of the universe. Every world spins in pain. If there is any kind of supreme being, I told myself, it is up to all of us to become his moral superior."

My dissatisfaction with the ending prevents Unseen Academicals from rising to the level of Night Watch, and it's a bit more uneven than the best books of the series. Still, though, this is great stuff; recommended to anyone who is reading the series. Followed in publication order by I Shall Wear Midnight. Rating: 8 out of 10

With the release of Libntlm version 1.8 the release tarball can be reproduced on several distributions. We also publish a signed minimal source-only tarball, produced by git-archive which is the same format used by Savannah, Codeberg, GitLab, GitHub and others. Reproducibility of both tarballs are tested continuously for regressions on GitLab through a CI/CD pipeline. If that wasn t enough to excite you, the Debian packages of Libntlm are now built from the reproducible minimal source-only tarball. The resulting binaries are hopefully reproducible on several architectures. What does that even mean? Why should you care? How you can do the same for your project? What are the open issues? Read on, dear reader This article describes my practical experiments with reproducible release artifacts, following up on my earlier thoughts that lead to discussion on Fosstodon and a patch by Janneke Nieuwenhuizen to make Guix tarballs reproducible that inspired me to some practical work. Let s look at how a maintainer release some software, and how a user can reproduce the released artifacts from the source code. Libntlm provides a shared library written in C and uses GNU Make, GNU Autoconf, GNU Automake, GNU Libtool and gnulib for build management, but these ideas should apply to most project and build system. The following illustrate the steps a maintainer would take to prepare a release:

git clone https://gitlab.com/gsasl/libntlm.git
cd libntlm
git checkout v1.8
./bootstrap
./configure
make distcheck
gpg -b libntlm-1.8.tar.gz

The generated files libntlm-1.8.tar.gz and libntlm-1.8.tar.gz.sig are published, and users download and use them. This is how the GNU project have been doing releases since the late 1980 s. That is a testament to how successful this pattern has been! These tarballs contain source code and some generated files, typically shell scripts generated by autoconf, makefile templates generated by automake, documentation in formats like Info, HTML, or PDF. Rarely do they contain binary object code, but historically that happened. The XZUtils incident illustrate that tarballs with files that are not included in the git archive offer an opportunity to disguise malicious backdoors. I blogged earlier how to mitigate this risk by using signed minimal source-only tarballs. The risk of hiding malware is not the only motivation to publish signed minimal source-only tarballs. With pre-generated content in tarballs, there is a risk that GNU/Linux distributions such as Trisquel, Guix, Debian/Ubuntu or Fedora ship generated files coming from the tarball into the binary *.deb or *.rpm package file. Typically the person packaging the upstream project never realized that some installed artifacts was not re-built through a typical autoconf -fi && ./configure && make install sequence, and never wrote the code to rebuild everything. This can also happen if the build rules are written but are buggy, shipping the old artifact. When a security problem is found, this can lead to time-consuming situations, as it may be that patching the relevant source code and rebuilding the package is not sufficient: the vulnerable generated object from the tarball would be shipped into the binary package instead of a rebuilt artifact. For architecture-specific binaries this rarely happens, since object code is usually not included in tarballs although for 10+ years I shipped the binary Java JAR file in the GNU Libidn release tarball, until I stopped shipping it. For interpreted languages and especially for generated content such as HTML, PDF, shell scripts this happens more than you would like. Publishing minimal source-only tarballs enable easier auditing of a project s code, to avoid the need to read through all generated files looking for malicious content. I have taken care to generate the source-only minimal tarball using git-archive. This is the same format that GitLab, GitHub etc offer for the automated download links on git tags. The minimal source-only tarballs can thus serve as a way to audit GitLab and GitHub download material! Consider if/when hosting sites like GitLab or GitHub has a security incident that cause generated tarballs to include a backdoor that is not present in the git repository. If people rely on the tag download artifact without verifying the maintainer PGP signature using GnuPG, this can lead to similar backdoor scenarios that we had for XZUtils but originated with the hosting provider instead of the release manager. This is even more concerning, since this attack can be mounted for some selected IP address that you want to target and not on everyone, thereby making it harder to discover. With all that discussion and rationale out of the way, let s return to the release process. I have added another step here:

make srcdist
gpg -b libntlm-1.8-src.tar.gz

Now the release is ready. I publish these four files in the Libntlm s Savannah Download area, but they can be uploaded to a GitLab/GitHub release area as well. These are the SHA256 checksums I got after building the tarballs on my Trisquel 11 aramo laptop:

91de864224913b9493c7a6cec2890e6eded3610d34c3d983132823de348ec2ca  libntlm-1.8-src.tar.gz
ce6569a47a21173ba69c990965f73eb82d9a093eb871f935ab64ee13df47fda1  libntlm-1.8.tar.gz

So how can you reproduce my artifacts? Here is how to reproduce them in a Ubuntu 22.04 container:

podman run -it --rm ubuntu:22.04
apt-get update
apt-get install -y --no-install-recommends autoconf automake libtool make git ca-certificates
git clone https://gitlab.com/gsasl/libntlm.git
cd libntlm
git checkout v1.8
./bootstrap
./configure
make dist srcdist
sha256sum libntlm-*.tar.gz

You should see the exact same SHA256 checksum values. Hooray! This works because Trisquel 11 and Ubuntu 22.04 uses the same version of git, autoconf, automake, and libtool. These tools do not guarantee the same output content for all versions, similar to how GNU GCC does not generate the same binary output for all versions. So there is still some delicate version pairing needed. Ideally, the artifacts should be possible to reproduce from the release artifacts themselves, and not only directly from git. It is possible to reproduce the full tarball in a AlmaLinux 8 container replace almalinux:8 with rockylinux:8 if you prefer RockyLinux:

podman run -it --rm almalinux:8
dnf update -y
dnf install -y make wget gcc
wget https://download.savannah.nongnu.org/releases/libntlm/libntlm-1.8.tar.gz
tar xfa libntlm-1.8.tar.gz
cd libntlm-1.8
./configure
make dist
sha256sum libntlm-1.8.tar.gz

The source-only minimal tarball can be regenerated on Debian 11:

podman run -it --rm debian:11
apt-get update
apt-get install -y --no-install-recommends make git ca-certificates
git clone https://gitlab.com/gsasl/libntlm.git
cd libntlm
git checkout v1.8
make -f cfg.mk srcdist
sha256sum libntlm-1.8-src.tar.gz 

As the Magnus Opus or chef-d uvre, let s recreate the full tarball directly from the minimal source-only tarball on Trisquel 11 replace docker.io/kpengboy/trisquel:11.0 with ubuntu:22.04 if you prefer.

podman run -it --rm docker.io/kpengboy/trisquel:11.0
apt-get update
apt-get install -y --no-install-recommends autoconf automake libtool make wget git ca-certificates
wget https://download.savannah.nongnu.org/releases/libntlm/libntlm-1.8-src.tar.gz
tar xfa libntlm-1.8-src.tar.gz
cd libntlm-v1.8
./bootstrap
./configure
make dist
sha256sum libntlm-1.8.tar.gz

Yay! You should now have great confidence in that the release artifacts correspond to what s in version control and also to what the maintainer intended to release. Your remaining job is to audit the source code for vulnerabilities, including the source code of the dependencies used in the build. You no longer have to worry about auditing the release artifacts. I find it somewhat amusing that the build infrastructure for Libntlm is now in a significantly better place than the code itself. Libntlm is written in old C style with plenty of string manipulation and uses broken cryptographic algorithms such as MD4 and single-DES. Remember folks: solving supply chain security issues has no bearing on what kind of code you eventually run. A clean gun can still shoot you in the foot. Side note on naming: GitLab exports tarballs with pathnames libntlm-v1.8/ (i.e.., PROJECT-TAG/) and I ve adopted the same pathnames, which means my libntlm-1.8-src.tar.gz tarballs are bit-by-bit identical to GitLab s exports and you can verify this with tools like diffoscope. GitLab name the tarball libntlm-v1.8.tar.gz (i.e., PROJECT-TAG.ARCHIVE) which I find too similar to the libntlm-1.8.tar.gz that we also publish. GitHub uses the same git archive style, but unfortunately they have logic that removes the v in the pathname so you will get a tarball with pathname libntlm-1.8/ instead of libntlm-v1.8/ that GitLab and I use. The content of the tarball is bit-by-bit identical, but the pathname and archive differs. Codeberg (running Forgejo) uses another approach: the tarball is called libntlm-v1.8.tar.gz (after the tag) just like GitLab, but the pathname inside the archive is libntlm/, otherwise the produced archive is bit-by-bit identical including timestamps. Savannah s CGIT interface uses archive name libntlm-1.8.tar.gz with pathname libntlm-1.8/, but otherwise file content is identical. Savannah s GitWeb interface provides snapshot links that are named after the git commit (e.g., libntlm-a812c2ca.tar.gz with libntlm-a812c2ca/) and I cannot find any tag-based download links at all. Overall, we are so close to get SHA256 checksum to match, but fail on pathname within the archive. I ve chosen to be compatible with GitLab regarding the content of tarballs but not on archive naming. From a simplicity point of view, it would be nice if everyone used PROJECT-TAG.ARCHIVE for the archive filename and PROJECT-TAG/ for the pathname within the archive. This aspect will probably need more discussion. Side note on git archive output: It seems different versions of git archive produce different results for the same repository. The version of git in Debian 11, Trisquel 11 and Ubuntu 22.04 behave the same. The version of git in Debian 12, AlmaLinux/RockyLinux 8/9, Alpine, ArchLinux, macOS homebrew, and upcoming Ubuntu 24.04 behave in another way. Hopefully this will not change that often, but this would invalidate reproducibility of these tarballs in the future, forcing you to use an old git release to reproduce the source-only tarball. Alas, GitLab and most other sites appears to be using modern git so the download tarballs from them would not match my tarballs even though the content would. Side note on ChangeLog: ChangeLog files were traditionally manually curated files with version history for a package. In recent years, several projects moved to dynamically generate them from git history (using tools like git2cl or gitlog-to-changelog). This has consequences for reproducibility of tarballs: you need to have the entire git history available! The gitlog-to-changelog tool also output different outputs depending on the time zone of the person using it, which arguable is a simple bug that can be fixed. However this entire approach is incompatible with rebuilding the full tarball from the minimal source-only tarball. It seems Libntlm s ChangeLog file died on the surgery table here. So how would a distribution build these minimal source-only tarballs? I happen to help on the libntlm package in Debian. It has historically used the generated tarballs as the source code to build from. This means that code coming from gnulib is vendored in the tarball. When a security problem is discovered in gnulib code, the security team needs to patch all packages that include that vendored code and rebuild them, instead of merely patching the gnulib package and rebuild all packages that rely on that particular code. To change this, the Debian libntlm package needs to Build-Depends on Debian s gnulib package. But there was one problem: similar to most projects that use gnulib, Libntlm depend on a particular git commit of gnulib, and Debian only ship one commit. There is no coordination about which commit to use. I have adopted gnulib in Debian, and add a git bundle to the *_all.deb binary package so that projects that rely on gnulib can pick whatever commit they need. This allow an no-network GNULIB_URL and GNULIB_REVISION approach when running Libntlm s ./bootstrap with the Debian gnulib package installed. Otherwise libntlm would pick up whatever latest version of gnulib that Debian happened to have in the gnulib package, which is not what the Libntlm maintainer intended to be used, and can lead to all sorts of version mismatches (and consequently security problems) over time. Libntlm in Debian is developed and tested on Salsa and there is continuous integration testing of it as well, thanks to the Salsa CI team. Side note on git bundles: unfortunately there appears to be no reproducible way to export a git repository into one or more files. So one unfortunate consequence of all this work is that the gnulib *.orig.tar.gz tarball in Debian is not reproducible any more. I have tried to get Git bundles to be reproducible but I never got it to work see my notes in gnulib s debian/README.source on this aspect. Of course, source tarball reproducibility has nothing to do with binary reproducibility of gnulib in Debian itself, fortunately. One open question is how to deal with the increased build dependencies that is triggered by this approach. Some people are surprised by this but I don t see how to get around it: if you depend on source code for tools in another package to build your package, it is a bad idea to hide that dependency. We ve done it for a long time through vendored code in non-minimal tarballs. Libntlm isn t the most critical project from a bootstrapping perspective, so adding git and gnulib as Build-Depends to it will probably be fine. However, consider if this pattern was used for other packages that uses gnulib such as coreutils, gzip, tar, bison etc (all are using gnulib) then they would all Build-Depends on git and gnulib. Cross-building those packages for a new architecture will therefor require git on that architecture first, which gets circular quick. The dependency on gnulib is real so I don t see that going away, and gnulib is a Architecture:all package. However, the dependency on git is merely a consequence of how the Debian gnulib package chose to make all gnulib git commits available to projects: through a git bundle. There are other ways to do this that doesn t require the git tool to extract the necessary files, but none that I found practical ideas welcome! Finally some brief notes on how this was implemented. Enabling bootstrappable source-only minimal tarballs via gnulib s ./bootstrap is achieved by using the GNULIB_REVISION mechanism, locking down the gnulib commit used. I have always disliked git submodules because they add extra steps and has complicated interaction with CI/CD. The reason why I gave up git submodules now is because the particular commit to use is not recorded in the git archive output when git submodules is used. So the particular gnulib commit has to be mentioned explicitly in some source code that goes into the git archive tarball. Colin Watson added the GNULIB_REVISION approach to ./bootstrap back in 2018, and now it no longer made sense to continue to use a gnulib git submodule. One alternative is to use ./bootstrap with --gnulib-srcdir or --gnulib-refdir if there is some practical problem with the GNULIB_URL towards a git bundle the GNULIB_REVISION in bootstrap.conf. The srcdist make rule is simple:

git archive --prefix=libntlm-v1.8/ -o libntlm-v1.8.tar.gz HEAD

Making the make dist generated tarball reproducible can be more complicated, however for Libntlm it was sufficient to make sure the modification times of all files were set deterministically to the timestamp of the last commit in the git repository. Interestingly there seems to be a couple of different ways to accomplish this, Guix doesn t support minimal source-only tarballs but rely on a .tarball-timestamp file inside the tarball. Paul Eggert explained what TZDB is using some time ago. The approach I m using now is fairly similar to the one I suggested over a year ago. If there are problems because all files in the tarball now use the same modification time, there is a solution by Bruno Haible that could be implemented. Side note on git tags: Some people may wonder why not verify a signed git tag instead of verifying a signed tarball of the git archive. Currently most git repositories uses SHA-1 for git commit identities, but SHA-1 is not a secure hash function. While current SHA-1 attacks can be detected and mitigated, there are fundamental doubts that a git SHA-1 commit identity uniquely refers to the same content that was intended. Verifying a git tag will never offer the same assurance, since a git tag can be moved or re-signed at any time. Verifying a git commit is better but then we need to trust SHA-1. Migrating git to SHA-256 would resolve this aspect, but most hosting sites such as GitLab and GitHub does not support this yet. There are other advantages to using signed tarballs instead of signed git commits or git tags as well, e.g., tar.gz can be a deterministically reproducible persistent stable offline storage format but .git sub-directory trees or git bundles do not offer this property. Doing continous testing of all this is critical to make sure things don t regress. Libntlm s pipeline definition now produce the generated libntlm-*.tar.gz tarballs and a checksum as a build artifact. Then I added the 000-reproducability job which compares the checksums and fails on mismatches. You can read its delicate output in the job for the v1.8 release. Right now we insists that builds on Trisquel 11 match Ubuntu 22.04, that PureOS 10 builds match Debian 11 builds, that AlmaLinux 8 builds match RockyLinux 8 builds, and AlmaLinux 9 builds match RockyLinux 9 builds. As you can see in pipeline job output, not all platforms lead to the same tarballs, but hopefully this state can be improved over time. There is also partial reproducibility, where the full tarball is reproducible across two distributions but not the minimal tarball, or vice versa. If this way of working plays out well, I hope to implement it in other projects too. What do you think? Happy Hacking!

Years ago, at what I think I remember was DebConf 15, I hacked for a while on debhelper to write build-ids to debian binary control files, so that the build-id (more specifically, the ELF note .note.gnu.build-id) wound up in the Debian apt archive metadata. I ve always thought this was super cool, and seeing as how Michael Stapelberg blogged some great pointers around the ecosystem, including the fancy new debuginfod service, and the find-dbgsym-packages helper, which uses these same headers, I don t think I m the only one. At work I ve been using a lot of rust, specifically, async rust using tokio. To try and work on my style, and to dig deeper into the how and why of the decisions made in these frameworks, I ve decided to hack up a project that I ve wanted to do ever since 2015 write a debug filesystem. Let s get to it.

Back to the Future Time to admit something. I really love Plan 9. It s just so good. So many ideas from Plan 9 are just so prescient, and everything just feels right. Not just right like, feels good like, correct. The bit that I ve always liked the most is 9p, the network protocol for serving a filesystem over a network. This leads to all sorts of fun programs, like the Plan 9 ftp client being a 9p server you mount the ftp server and access files like any other files. It s kinda like if fuse were more fully a part of how the operating system worked, but fuse is all running client-side. With 9p there s a single client, and different servers that you can connect to, which may be backed by a hard drive, remote resources over something like SFTP, FTP, HTTP or even purely synthetic. The interesting (maybe sad?) part here is that 9p wound up outliving Plan 9 in terms of adoption 9p is in all sorts of places folks don t usually expect. For instance, the Windows Subsystem for Linux uses the 9p protocol to share files between Windows and Linux. ChromeOS uses it to share files with Crostini, and qemu uses 9p (virtio-p9) to share files between guest and host. If you re noticing a pattern here, you d be right; for some reason 9p is the go-to protocol to exchange files between hypervisor and guest. Why? I have no idea, except maybe due to being designed well, simple to implement, and it s a lot easier to validate the data being shared and validate security boundaries. Simplicity has its value. As a result, there s a lot of lingering 9p support kicking around. Turns out Linux can even handle mounting 9p filesystems out of the box. This means that I can deploy a filesystem to my LAN or my localhost by running a process on top of a computer that needs nothing special, and mount it over the network on an unmodified machine unlike fuse, where you d need client-specific software to run in order to mount the directory. For instance, let s mount a 9p filesystem running on my localhost machine, serving requests on 127.0.0.1:564 (tcp) that goes by the name mountpointname to /mnt.

$ mount -t 9p \
-o trans=tcp,port=564,version=9p2000.u,aname=mountpointname \
127.0.0.1 \
/mnt

Linux will mount away, and attach to the filesystem as the root user, and by default, attach to that mountpoint again for each local user that attempts to use it. Nifty, right? I think so. The server is able to keep track of per-user access and authorization along with the host OS.

WHEREIN I STYX WITH IT Since I wanted to push myself a bit more with rust and tokio specifically, I opted to implement the whole stack myself, without third party libraries on the critical path where I could avoid it. The 9p protocol (sometimes called Styx, the original name for it) is incredibly simple. It s a series of client to server requests, which receive a server to client response. These are, respectively, T messages, which transmit a request to the server, which trigger an R message in response (Reply messages). These messages are TLV payload with a very straight forward structure so straight forward, in fact, that I was able to implement a working server off nothing more than a handful of man pages. Later on after the basics worked, I found a more complete spec page that contains more information about the unix specific variant that I opted to use (9P2000.u rather than 9P2000) due to the level of Linux specific support for the 9P2000.u variant over the 9P2000 protocol.

MR ROBOTO The backend stack over at zoo is rust and tokio running i/o for an HTTP and WebRTC server. I figured I d pick something fairly similar to write my filesystem with, since 9P can be implemented on basically anything with I/O. That means tokio tcp server bits, which construct and use a 9p server, which has an idiomatic Rusty API that partially abstracts the raw R and T messages, but not so much as to cause issues with hiding implementation possibilities. At each abstraction level, there s an escape hatch allowing someone to implement any of the layers if required. I called this framework arigato which can be found over on docs.rs and crates.io.

/// Simplified version of the arigato File trait; this isn't actually
/// the same trait; there's some small cosmetic differences. The
/// actual trait can be found at:
///
/// https://docs.rs/arigato/latest/arigato/server/trait.File.html
trait File  
/// OpenFile is the type returned by this File via an Open call.
 type OpenFile: OpenFile;
/// Return the 9p Qid for this file. A file is the same if the Qid is
 /// the same. A Qid contains information about the mode of the file,
 /// version of the file, and a unique 64 bit identifier.
 fn qid(&self) -> Qid;
/// Construct the 9p Stat struct with metadata about a file.
 async fn stat(&self) -> FileResult<Stat>;
/// Attempt to update the file metadata.
 async fn wstat(&mut self, s: &Stat) -> FileResult<()>;
/// Traverse the filesystem tree.
 async fn walk(&self, path: &[&str]) -> FileResult<(Option<Self>, Vec<Self>)>;
/// Request that a file's reference be removed from the file tree.
 async fn unlink(&mut self) -> FileResult<()>;
/// Create a file at a specific location in the file tree.
 async fn create(
&mut self,
name: &str,
perm: u16,
ty: FileType,
mode: OpenMode,
extension: &str,
) -> FileResult<Self>;
/// Open the File, returning a handle to the open file, which handles
 /// file i/o. This is split into a second type since it is genuinely
 /// unrelated -- and the fact that a file is Open or Closed can be
 /// handled by the  arigato  server for us.
 async fn open(&mut self, mode: OpenMode) -> FileResult<Self::OpenFile>;
 
/// Simplified version of the arigato OpenFile trait; this isn't actually
/// the same trait; there's some small cosmetic differences. The
/// actual trait can be found at:
///
/// https://docs.rs/arigato/latest/arigato/server/trait.OpenFile.html
trait OpenFile  
/// iounit to report for this file. The iounit reported is used for Read
 /// or Write operations to signal, if non-zero, the maximum size that is
 /// guaranteed to be transferred atomically.
 fn iounit(&self) -> u32;
/// Read some number of bytes up to  buf.len()  from the provided
 ///  offset  of the underlying file. The number of bytes read is
 /// returned.
 async fn read_at(
&mut self,
buf: &mut [u8],
offset: u64,
) -> FileResult<u32>;
/// Write some number of bytes up to  buf.len()  from the provided
 ///  offset  of the underlying file. The number of bytes written
 /// is returned.
 fn write_at(
&mut self,
buf: &mut [u8],
offset: u64,
) -> FileResult<u32>;
 

Thanks, decade ago paultag! Let s do it! Let s use arigato to implement a 9p filesystem we ll call debugfs that will serve all the debug files shipped according to the Packages metadata from the apt archive. We ll fetch the Packages file and construct a filesystem based on the reported Build-Id entries. For those who don t know much about how an apt repo works, here s the 2-second crash course on what we re doing. The first is to fetch the Packages file, which is specific to a binary architecture (such as amd64, arm64 or riscv64). That architecture is specific to a component (such as main, contrib or non-free). That component is specific to a suite, such as stable, unstable or any of its aliases (bullseye, bookworm, etc). Let s take a look at the Packages.xz file for the unstable-debug suite, main component, for all amd64 binaries.

$ curl \
https://deb.debian.org/debian-debug/dists/unstable-debug/main/binary-amd64/Packages.xz \
  unxz

This will return the Debian-style rfc2822-like headers, which is an export of the metadata contained inside each .deb file which apt (or other tools that can use the apt repo format) use to fetch information about debs. Let s take a look at the debug headers for the netlabel-tools package in unstable which is a package named netlabel-tools-dbgsym in unstable-debug.

Package: netlabel-tools-dbgsym
Source: netlabel-tools (0.30.0-1)
Version: 0.30.0-1+b1
Installed-Size: 79
Maintainer: Paul Tagliamonte <paultag@debian.org>
Architecture: amd64
Depends: netlabel-tools (= 0.30.0-1+b1)
Description: debug symbols for netlabel-tools
Auto-Built-Package: debug-symbols
Build-Ids: e59f81f6573dadd5d95a6e4474d9388ab2777e2a
Description-md5: a0e587a0cf730c88a4010f78562e6db7
Section: debug
Priority: optional
Filename: pool/main/n/netlabel-tools/netlabel-tools-dbgsym_0.30.0-1+b1_amd64.deb
Size: 62776
SHA256: 0e9bdb087617f0350995a84fb9aa84541bc4df45c6cd717f2157aa83711d0c60

So here, we can parse the package headers in the Packages.xz file, and store, for each Build-Id, the Filename where we can fetch the .deb at. Each .deb contains a number of files but we re only really interested in the files inside the .deb located at or under /usr/lib/debug/.build-id/, which you can find in debugfs under rfc822.rs. It s crude, and very single-purpose, but I m feeling a bit lazy.

Who needs dpkg?! For folks who haven t seen it yet, a .deb file is a special type of .ar file, that contains (usually) three files inside debian-binary, control.tar.xz and data.tar.xz. The core of an .ar file is a fixed size (60 byte) entry header, followed by the specified size number of bytes.

[8 byte .ar file magic]
[60 byte entry header]
[N bytes of data]
[60 byte entry header]
[N bytes of data]
[60 byte entry header]
[N bytes of data]
...

First up was to implement a basic ar parser in ar.rs. Before we get into using it to parse a deb, as a quick diversion, let s break apart a .deb file by hand something that is a bit of a rite of passage (or at least it used to be? I m getting old) during the Debian nm (new member) process, to take a look at where exactly the .debug file lives inside the .deb file.

$ ar x netlabel-tools-dbgsym_0.30.0-1+b1_amd64.deb
$ ls
control.tar.xz debian-binary
data.tar.xz netlabel-tools-dbgsym_0.30.0-1+b1_amd64.deb
$ tar --list -f data.tar.xz   grep '.debug$'
./usr/lib/debug/.build-id/e5/9f81f6573dadd5d95a6e4474d9388ab2777e2a.debug

Since we know quite a bit about the structure of a .deb file, and I had to implement support from scratch anyway, I opted to implement a (very!) basic debfile parser using HTTP Range requests. HTTP Range requests, if supported by the server (denoted by a accept-ranges: bytes HTTP header in response to an HTTP HEAD request to that file) means that we can add a header such as range: bytes=8-68 to specifically request that the returned GET body be the byte range provided (in the above case, the bytes starting from byte offset 8 until byte offset 68). This means we can fetch just the ar file entry from the .deb file until we get to the file inside the .deb we are interested in (in our case, the data.tar.xz file) at which point we can request the body of that file with a final range request. I wound up writing a struct to handle a read_at-style API surface in hrange.rs, which we can pair with ar.rs above and start to find our data in the .deb remotely without downloading and unpacking the .deb at all. After we have the body of the data.tar.xz coming back through the HTTP response, we get to pipe it through an xz decompressor (this kinda sucked in Rust, since a tokio AsyncRead is not the same as an http Body response is not the same as std::io::Read, is not the same as an async (or sync) Iterator is not the same as what the xz2 crate expects; leading me to read blocks of data to a buffer and stuff them through the decoder by looping over the buffer for each lzma2 packet in a loop), and tarfile parser (similarly troublesome). From there we get to iterate over all entries in the tarfile, stopping when we reach our file of interest. Since we can t seek, but gdb needs to, we ll pull it out of the stream into a Cursor<Vec<u8>> in-memory and pass a handle to it back to the user. From here on out its a matter of gluing together a File traited struct in debugfs, and serving the filesystem over TCP using arigato. Done deal!

A quick diversion about compression I was originally hoping to avoid transferring the whole tar file over the network (and therefore also reading the whole debug file into ram, which objectively sucks), but quickly hit issues with figuring out a way around seeking around an xz file. What s interesting is xz has a great primitive to solve this specific problem (specifically, use a block size that allows you to seek to the block as close to your desired seek position just before it, only discarding at most block size - 1 bytes), but data.tar.xz files generated by dpkg appear to have a single mega-huge block for the whole file. I don t know why I would have expected any different, in retrospect. That means that this now devolves into the base case of How do I seek around an lzma2 compressed data stream ; which is a lot more complex of a question. Thankfully, notoriously brilliant tianon was nice enough to introduce me to Jon Johnson who did something super similar adapted a technique to seek inside a compressed gzip file, which lets his service oci.dag.dev seek through Docker container images super fast based on some prior work such as soci-snapshotter, gztool, and zran.c. He also pulled this party trick off for apk based distros over at apk.dag.dev, which seems apropos. Jon was nice enough to publish a lot of his work on this specifically in a central place under the name targz on his GitHub, which has been a ton of fun to read through. The gist is that, by dumping the decompressor s state (window of previous bytes, in-memory data derived from the last N-1 bytes) at specific checkpoints along with the compressed data stream offset in bytes and decompressed offset in bytes, one can seek to that checkpoint in the compressed stream and pick up where you left off creating a similar block mechanism against the wishes of gzip. It means you d need to do an O(n) run over the file, but every request after that will be sped up according to the number of checkpoints you ve taken. Given the complexity of xz and lzma2, I don t think this is possible for me at the moment especially given most of the files I ll be requesting will not be loaded from again especially when I can just cache the debug header by Build-Id. I want to implement this (because I m generally curious and Jon has a way of getting someone excited about compression schemes, which is not a sentence I thought I d ever say out loud), but for now I m going to move on without this optimization. Such a shame, since it kills a lot of the work that went into seeking around the .deb file in the first place, given the debian-binary and control.tar.gz members are so small.

The Good First, the good news right? It works! That s pretty cool. I m positive my younger self would be amused and happy to see this working; as is current day paultag. Let s take debugfs out for a spin! First, we need to mount the filesystem. It even works on an entirely unmodified, stock Debian box on my LAN, which is huge. Let s take it for a spin:

$ mount \
-t 9p \
-o trans=tcp,version=9p2000.u,aname=unstable-debug \
192.168.0.2 \
/usr/lib/debug/.build-id/

And, let s prove to ourselves that this actually mounted before we go trying to use it:

$ mount   grep build-id
192.168.0.2 on /usr/lib/debug/.build-id type 9p (rw,relatime,aname=unstable-debug,access=user,trans=tcp,version=9p2000.u,port=564)

Slick. We ve got an open connection to the server, where our host will keep a connection alive as root, attached to the filesystem provided in aname. Let s take a look at it.

$ ls /usr/lib/debug/.build-id/
00 0d 1a 27 34 41 4e 5b 68 75 82 8E 9b a8 b5 c2 CE db e7 f3
01 0e 1b 28 35 42 4f 5c 69 76 83 8f 9c a9 b6 c3 cf dc E7 f4
02 0f 1c 29 36 43 50 5d 6a 77 84 90 9d aa b7 c4 d0 dd e8 f5
03 10 1d 2a 37 44 51 5e 6b 78 85 91 9e ab b8 c5 d1 de e9 f6
04 11 1e 2b 38 45 52 5f 6c 79 86 92 9f ac b9 c6 d2 df ea f7
05 12 1f 2c 39 46 53 60 6d 7a 87 93 a0 ad ba c7 d3 e0 eb f8
06 13 20 2d 3a 47 54 61 6e 7b 88 94 a1 ae bb c8 d4 e1 ec f9
07 14 21 2e 3b 48 55 62 6f 7c 89 95 a2 af bc c9 d5 e2 ed fa
08 15 22 2f 3c 49 56 63 70 7d 8a 96 a3 b0 bd ca d6 e3 ee fb
09 16 23 30 3d 4a 57 64 71 7e 8b 97 a4 b1 be cb d7 e4 ef fc
0a 17 24 31 3e 4b 58 65 72 7f 8c 98 a5 b2 bf cc d8 E4 f0 fd
0b 18 25 32 3f 4c 59 66 73 80 8d 99 a6 b3 c0 cd d9 e5 f1 fe
0c 19 26 33 40 4d 5a 67 74 81 8e 9a a7 b4 c1 ce da e6 f2 ff

Outstanding. Let s try using gdb to debug a binary that was provided by the Debian archive, and see if it ll load the ELF by build-id from the right .deb in the unstable-debug suite:

$ gdb -q /usr/sbin/netlabelctl
Reading symbols from /usr/sbin/netlabelctl...
Reading symbols from /usr/lib/debug/.build-id/e5/9f81f6573dadd5d95a6e4474d9388ab2777e2a.debug...
(gdb)

Yes! Yes it will!

$ file /usr/lib/debug/.build-id/e5/9f81f6573dadd5d95a6e4474d9388ab2777e2a.debug
/usr/lib/debug/.build-id/e5/9f81f6573dadd5d95a6e4474d9388ab2777e2a.debug: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, interpreter *empty*, BuildID[sha1]=e59f81f6573dadd5d95a6e4474d9388ab2777e2a, for GNU/Linux 3.2.0, with debug_info, not stripped

The Bad Linux s support for 9p is mainline, which is great, but it s not robust. Network issues or server restarts will wedge the mountpoint (Linux can t reconnect when the tcp connection breaks), and things that work fine on local filesystems get translated in a way that causes a lot of network chatter for instance, just due to the way the syscalls are translated, doing an ls, will result in a stat call for each file in the directory, even though linux had just got a stat entry for every file while it was resolving directory names. On top of that, Linux will serialize all I/O with the server, so there s no concurrent requests for file information, writes, or reads pending at the same time to the server; and read and write throughput will degrade as latency increases due to increasing round-trip time, even though there are offsets included in the read and write calls. It works well enough, but is frustrating to run up against, since there s not a lot you can do server-side to help with this beyond implementing the 9P2000.L variant (which, maybe is worth it).

The Ugly Unfortunately, we don t know the file size(s) until we ve actually opened the underlying tar file and found the correct member, so for most files, we don t know the real size to report when getting a stat. We can t parse the tarfiles for every stat call, since that d make ls even slower (bummer). Only hiccup is that when I report a filesize of zero, gdb throws a bit of a fit; let s try with a size of 0 to start:

$ ls -lah /usr/lib/debug/.build-id/e5/9f81f6573dadd5d95a6e4474d9388ab2777e2a.debug
-r--r--r-- 1 root root 0 Dec 31 1969 /usr/lib/debug/.build-id/e5/9f81f6573dadd5d95a6e4474d9388ab2777e2a.debug
$ gdb -q /usr/sbin/netlabelctl
Reading symbols from /usr/sbin/netlabelctl...
Reading symbols from /usr/lib/debug/.build-id/e5/9f81f6573dadd5d95a6e4474d9388ab2777e2a.debug...
warning: Discarding section .note.gnu.build-id which has a section size (24) larger than the file size [in module /usr/lib/debug/.build-id/e5/9f81f6573dadd5d95a6e4474d9388ab2777e2a.debug]
[...]

This obviously won t work since gdb will throw away all our hard work because of stat s output, and neither will loading the real size of the underlying file. That only leaves us with hardcoding a file size and hope nothing else breaks significantly as a result. Let s try it again:

$ ls -lah /usr/lib/debug/.build-id/e5/9f81f6573dadd5d95a6e4474d9388ab2777e2a.debug
-r--r--r-- 1 root root 954M Dec 31 1969 /usr/lib/debug/.build-id/e5/9f81f6573dadd5d95a6e4474d9388ab2777e2a.debug
$ gdb -q /usr/sbin/netlabelctl
Reading symbols from /usr/sbin/netlabelctl...
Reading symbols from /usr/lib/debug/.build-id/e5/9f81f6573dadd5d95a6e4474d9388ab2777e2a.debug...
(gdb)

Much better. I mean, terrible but better. Better for now, anyway.

Kilroy was here Do I think this is a particularly good idea? I mean; kinda. I m probably going to make some fun 9p arigato-based filesystems for use around my LAN, but I don t think I ll be moving to use debugfs until I can figure out how to ensure the connection is more resilient to changing networks, server restarts and fixes on i/o performance. I think it was a useful exercise and is a pretty great hack, but I don t think this ll be shipping anywhere anytime soon. Along with me publishing this post, I ve pushed up all my repos; so you should be able to play along at home! There s a lot more work to be done on arigato; but it does handshake and successfully export a working 9P2000.u filesystem. Check it out on on my github at arigato, debugfs and also on crates.io and docs.rs. At least I can say I was here and I got it working after all these years.

Getting the Belgian eID to work on Linux systems should be fairly easy, although some people do struggle with it. For that reason, there is a lot of third-party documentation out there in the form of blog posts, wiki pages, and other kinds of things. Unfortunately, some of this documentation is simply wrong. Written by people who played around with things until it kind of worked, sometimes you get a situation where something that used to work in the past (but wasn't really necessary) now stopped working, but it's still added to a number of locations as though it were the gospel. And then people follow these instructions and now things don't work anymore. One of these revolves around OpenSC. OpenSC is an open source smartcard library that has support for a pretty large number of smartcards, amongst which the Belgian eID. It provides a PKCS#11 module as well as a number of supporting tools. For those not in the know, PKCS#11 is a standardized C API for offloading cryptographic operations. It is an API that can be used when talking to a hardware cryptographic module, in order to make that module perform some actions, and it is especially popular in the open source world, with support in NSS, amongst others. This library is written and maintained by mozilla, and is a low-level cryptographic library that is used by Firefox (on all platforms it supports) as well as by Google Chrome and other browsers based on that (but only on Linux, and as I understand it, only for linking with smartcards; their BoringSSL library is used for other things). The official eID software that we ship through eid.belgium.be, also known as "BeID", provides a PKCS#11 module for the Belgian eID, as well as a number of support tools to make interacting with the card easier, such as the "eID viewer", which provides the ability to read data from the card, and validate their signatures. While the very first public version of this eID PKCS#11 module was originally based on OpenSC, it has since been reimplemented as a PKCS#11 module in its own right, with no lineage to OpenSC whatsoever anymore. About five years ago, the Belgian eID card was renewed. At the time, a new physical appearance was the most obvious difference with the old card, but there were also some technical, on-chip, differences that are not so apparent. The most important one here, although it is not the only one, is the fact that newer eID cards now use a NIST P-384 elliptic curve-based private keys, rather than the RSA-based ones that were used in the past. This change required some changes to any PKCS#11 module that supports the eID; both the BeID one, as well as the OpenSC card-belpic driver that is written in support of the Belgian eID. Obviously, the required changes were implemented for the BeID module; however, the OpenSC card-belpic driver was not updated. While I did do some preliminary work on the required changes, I was unable to get it to work, and eventually other things took up my time so I never finished the implementation. If someone would like to finish the work that I started, the preliminal patch that I wrote could be a good start -- but like I said, it doesn't yet work. Also, you'll probably be interested in the official documentation of the eID card. Unfortunately, in the mean time someone added the Applet 1.8 ATR to the card-belpic.c file, without also implementing the required changes to the driver so that the PKCS#11 driver actually supports the eID card. The result of this is that if you have OpenSC installed in NSS for either Firefox or any Chromium-based browser, and it gets picked up before the BeID PKCS#11 module, then NSS will stop looking and pass all crypto operations to the OpenSC PKCS#11 module rather than to the official eID PKCS#11 module, and things will not work at all, causing a lot of confusion. I have therefore taken the following two steps:

1. The official eID packages now conflict with the OpenSC PKCS#11 module. Specifically only the PKCS#11 module, not the rest of OpenSC, so you can theoretically still use its tools. This means that once we release this new version of the eID software, when you do an upgrade and you have OpenSC installed, it will remove the PKCS#11 module and anything that depends on it. This is normal and expected.
2. I have filed a pull request against OpenSC that removes the Applet 1.8 ATR from the driver, so that OpenSC will stop claiming that it supports the 1.8 applet.

When the pull request is accepted, we will update the official eID software to make the conflict versioned, so that as soon as it works again you will again be able to install the OpenSC and BeID packages at the same time. In the mean time, if you have the OpenSC PKCS#11 module installed on your system, and your eID authentication does not work, try removing it.

Now that we are back from our six month period in Argentina, we decided to adopt a kitten, to bring more diversity into our lives. Perhaps this little girl will teach us to think outside the box! Yesterday we witnessed a solar eclipse Mexico City was not in the totality range (we reached ~80%), but it was a great experience to go with the kids. A couple dozen thousand people gathered for a massive picnic in las islas, the main area inside our university campus. Afterwards, we went briefly back home, then crossed the city to fetch the little kitten. Of course, the kids were unanimous: Her name is Eclipse.

Those of you who haven t been in IT for far, far too long might not know that next month will be the 16th(!) anniversary of the disclosure of what was, at the time, a fairly earth-shattering revelation: that for about 18 months, the Debian OpenSSL package was generating entirely predictable private keys. The recent xz-stential threat (thanks to @nixCraft for making me aware of that one), has got me thinking about my own serendipitous interaction with a major vulnerability. Given that the statute of limitations has (probably) run out, I thought I d share it as a tale of how huh, that s weird can be a powerful threat-hunting tool but only if you ve got the time to keep pulling at the thread.

Prelude to an Adventure Our story begins back in March 2008. I was working at Engine Yard (EY), a now largely-forgotten Rails-focused hosting company, which pioneered several advances in Rails application deployment. Probably EY s greatest claim to lasting fame is that they helped launch a little code hosting platform you might have heard of, by providing them free infrastructure when they were little more than a glimmer in the Internet s eye. I am, of course, talking about everyone s favourite Microsoft product: GitHub. Since GitHub was in the right place, at the right time, with a compelling product offering, they quickly started to gain traction, and grow their userbase. With growth comes challenges, amongst them the one we re focusing on today: SSH login times. Then, as now, GitHub provided SSH access to the git repos they hosted, by SSHing to git@github.com with publickey authentication. They were using the standard way that everyone manages SSH keys: the ~/.ssh/authorized_keys file, and that became a problem as the number of keys started to grow. The way that SSH uses this file is that, when a user connects and asks for publickey authentication, SSH opens the ~/.ssh/authorized_keys file and scans all of the keys listed in it, looking for a key which matches the key that the user presented. This linear search is normally not a huge problem, because nobody in their right mind puts more than a few keys in their ~/.ssh/authorized_keys, right?

Of course, as a popular, rapidly-growing service, GitHub was gaining users at a fair clip, to the point that the one big file that stored all the SSH keys was starting to visibly impact SSH login times. This problem was also not going to get any better by itself. Something Had To Be Done. EY management was keen on making sure GitHub ran well, and so despite it not really being a hosting problem, they were willing to help fix this problem. For some reason, the late, great, Ezra Zygmuntowitz pointed GitHub in my direction, and let me take the time to really get into the problem with the GitHub team. After examining a variety of different possible solutions, we came to the conclusion that the least-worst option was to patch OpenSSH to lookup keys in a MySQL database, indexed on the key fingerprint. We didn t take this decision on a whim it wasn t a case of yeah, sure, let s just hack around with OpenSSH, what could possibly go wrong? . We knew it was potentially catastrophic if things went sideways, so you can imagine how much worse the other options available were. Ensuring that this wouldn t compromise security was a lot of the effort that went into the change. In the end, though, we rolled it out in early April, and lo! SSH logins were fast, and we were pretty sure we wouldn t have to worry about this problem for a long time to come. Normally, you d think patching OpenSSH to make mass SSH logins super fast would be a good story on its own. But no, this is just the opening scene.

Chekov s Gun Makes its Appearance Fast forward a little under a month, to the first few days of May 2008. I get a message from one of the GitHub team, saying that somehow users were able to access other users repos over SSH. Naturally, as we d recently rolled out the OpenSSH patch, which touched this very thing, the code I d written was suspect number one, so I was called in to help.

They're called The Usual Suspects for a reason, but sometimes, it really is Keyser S ze

Eventually, after more than a little debugging, we discovered that, somehow, there were two users with keys that had the same key fingerprint. This absolutely shouldn t happen it s a bit like winning the lottery twice in a row¹ unless the users had somehow shared their keys with each other, of course. Still, it was worth investigating, just in case it was a web application bug, so the GitHub team reached out to the users impacted, to try and figure out what was going on. The users professed no knowledge of each other, neither admitted to publicising their key, and couldn t offer any explanation as to how the other person could possibly have gotten their key. Then things went from weird to what the ? . Because another pair of users showed up, sharing a key fingerprint but it was a different shared key fingerprint. The odds now have gone from winning the lottery multiple times in a row to as close to this literally cannot happen as makes no difference.

Once we were really, really confident that the OpenSSH patch wasn t the cause of the problem, my involvement in the problem basically ended. I wasn t a GitHub employee, and EY had plenty of other customers who needed my help, so I wasn t able to stay deeply involved in the on-going investigation of The Mystery of the Duplicate Keys. However, the GitHub team did keep talking to the users involved, and managed to determine the only apparent common factor was that all the users claimed to be using Debian or Ubuntu systems, which was where their SSH keys would have been generated. That was as far as the investigation had really gotten, when along came May 13, 2008.

Chekov s Gun Goes Off With the publication of DSA-1571-1, everything suddenly became clear. Through a well-meaning but ultimately disasterous cleanup of OpenSSL s randomness generation code, the Debian maintainer had inadvertently reduced the number of possible keys that could be generated by a given user from bazillions to a little over 32,000. With so many people signing up to GitHub some of them no doubt following best practice and freshly generating a separate key it s unsurprising that some collisions occurred. You can imagine the sense of oooooooh, so that s what s going on! that rippled out once the issue was understood. I was mostly glad that we had conclusive evidence that my OpenSSH patch wasn t at fault, little knowing how much more contact I was to have with Debian weak keys in the future, running a huge store of known-compromised keys and using them to find misbehaving Certificate Authorities, amongst other things.

Lessons Learned While I ve not found a description of exactly when and how Luciano Bello discovered the vulnerability that became CVE-2008-0166, I presume he first came across it some time before it was disclosed likely before GitHub tripped over it. The stable Debian release that included the vulnerable code had been released a year earlier, so there was plenty of time for Luciano to have discovered key collisions and go hmm, I wonder what s going on here? , then keep digging until the solution presented itself. The thought hmm, that s odd , followed by intense investigation, leading to the discovery of a major flaw is also what ultimately brought down the recent XZ backdoor. The critical part of that sequence is the ability to do that intense investigation, though. When I reflect on my brush with the Debian weak keys vulnerability, what sticks out to me is the fact that I didn t do the deep investigation. I wonder if Luciano hadn t found it, how long it might have been before it was found. The GitHub team would have continued investigating, presumably, and perhaps they (or I) would have eventually dug deep enough to find it. But we were all super busy myself, working support tickets at EY, and GitHub feverishly building features and fighting the fires in their rapidly-growing service. As it was, Luciano was able to take the time to dig in and find out what was happening, but just like the XZ backdoor, I feel like we, as an industry, got a bit lucky that someone with the skills, time, and energy was on hand at the right time to make a huge difference. It s a luxury to be able to take the time to really dig into a problem, and it s a luxury that most of us rarely have. Perhaps an understated takeaway is that somehow we all need to wrestle back some time to follow our hunches and really dig into the things that make us go hmm .

Support My Hunches If you d like to help me be able to do intense investigations of mysterious software phenomena, you can shout me a refreshing beverage on ko-fi.

---

1. the odds are actually probably more like winning the lottery about twenty times in a row. The numbers involved are staggeringly huge, so it s easiest to just approximate it as really, really unlikely .

tl;dr: Don t just apt install rustc cargo. Either do that and make sure to use only Rust libraries from your distro (with the tiresome config runes below); or, just use rustup.

• Don t do the obvious thing; it s never what you want
  • Q. Download and run whatever code from the internet?
• Option 1: WTF, no I don t want curl bash
• Option 2: Biting the curl bash bullet
  • Privilege separation
• OMG what a mess

Don t do the obvious thing; it s never what you want Debian ships a Rust compiler, and a large number of Rust libraries. But if you just do things the obvious default way, with apt install rustc cargo, you will end up using Debian s compiler but upstream libraries, directly and uncurated from crates.io. This is not what you want. There are about two reasonable things to do, depending on your preferences. Q. Download and run whatever code from the internet? The key question is this: Are you comfortable downloading code, directly from hundreds of upstream Rust package maintainers, and running it ? That s what cargo does. It s one of the main things it s for. Debian s cargo behaves, in this respect, just like upstream s. Let me say that again: Debian s cargo promiscuously downloads code from crates.io just like upstream cargo. So if you use Debian s cargo in the most obvious way, you are still downloading and running all those random libraries. The only thing you re avoiding downloading is the Rust compiler itself, which is precisely the part that is most carefully maintained, and of least concern. Debian s cargo can even download from crates.io when you re building official Debian source packages written in Rust: if you run dpkg-buildpackage, the downloading is suppressed; but a plain cargo build will try to obtain and use dependencies from the upstream ecosystem. ( Happily , if you do this, it s quite likely to bail out early due to version mismatches, before actually downloading anything.) Option 1: WTF, no I don t want curl bash OK, but then you must limit yourself to libraries available within Debian. Each Debian release provides a curated set. It may or may not be sufficient for your needs. Many capable programs can be written using the packages in Debian. But any upstream Rust project that you encounter is likely to be a pain to get working, unless their maintainers specifically intend to support this. (This is fairly rare, and the Rust tooling doesn t make it easy.) To go with this plan, apt install rustc cargo and put this in your configuration, in $HOME/.cargo/config.toml:

[source.debian-packages]
directory = "/usr/share/cargo/registry"
[source.crates-io]
replace-with = "debian-packages"

This causes cargo to look in /usr/share for dependencies, rather than downloading them from crates.io. You must then install the librust-FOO-dev packages for each of your dependencies, with apt. This will allow you to write your own program in Rust, and build it using cargo build. Option 2: Biting the curl bash bullet If you want to build software that isn t specifically targeted at Debian s Rust you will probably need to use packages from crates.io, not from Debian. If you re doing to do that, there is little point not using rustup to get the latest compiler. rustup s install rune is alarming, but cargo will be doing exactly the same kind of thing, only worse (because it trusts many more people) and more hidden. So in this case: do run the curl bash install rune. Hopefully the Rust project you are trying to build have shipped a Cargo.lock; that contains hashes of all the dependencies that they last used and tested. If you run cargo build --locked, cargo will only use those versions, which are hopefully OK. And you can run cargo audit to see if there are any reported vulnerabilities or problems. But you ll have to bootstrap this with cargo install --locked cargo-audit; cargo-audit is from the RUSTSEC folks who do care about these kind of things, so hopefully running their code (and their dependencies) is fine. Note the --locked which is needed because cargo s default behaviour is wrong. Privilege separation This approach is rather alarming. For my personal use, I wrote a privsep tool which allows me to run all this upstream Rust code as a separate user. That tool is nailing-cargo. It s not particularly well productised, or tested, but it does work for at least one person besides me. You may wish to try it out, or consider alternative arrangements. Bug reports and patches welcome. OMG what a mess Indeed. There are large number of technical and social factors at play. cargo itself is deeply troubling, both in principle, and in detail. I often find myself severely disappointed with its maintainers decisions. In mitigation, much of the wider Rust upstream community does takes this kind of thing very seriously, and often makes good choices. RUSTSEC is one of the results. Debian s technical arrangements for Rust packaging are quite dysfunctional, too: IMO the scheme is based on fundamentally wrong design principles. But, the Debian Rust packaging team is dynamic, constantly working the update treadmills; and the team is generally welcoming and helpful. Sadly last time I explored the possibility, the Debian Rust Team didn t have the appetite for more fundamental changes to the workflow (including, for example, changes to dependency version handling). Significant improvements to upstream cargo s approach seem unlikely, too; we can only hope that eventually someone might manage to supplant it.

edited 2024-03-21 21:49 to add a cut tag

comments

This post is the second and final part of my Malaysia-Thailand trip. Feel free to check out the Malaysia part here if you haven t already. Kuala Lumpur to Bangkok is around 1500 km by road, and so I took a Malaysian Airlines flight to travel to Bangkok. The flight staff at the Kuala Lumpur only asked me for a return/onward flight and Thailand immigration asked a few questions but did not check any documents (obviously they checked and stamped my passport ;)). The currency of Thailand is the Thai baht, and 1 Thai baht = 2.5 Indian Rupees. The Thailand time is 1.5 hours ahead of Indian time (For example, if it is 12 noon in India, it will be 13:30 in Thailand). I landed in Bangkok at around 3 PM local time. Fletcher was in Bangkok that time, leaving for Pattaya and we had booked the same hostel. So I took a bus to Pattaya from the airport. The next bus for which the tickets were available was at 7 PM, so I took tickets for that one. The bus ticket cost was 143 Thai Baht. I didn t buy SIM at the airport, thinking there must be better deals in the city. As a consequence, there was no way to contact Fletcher through internet. Although I had a few minutes call remaining out of my international roaming pack.

A welcome sign at Bangkok's Suvarnabhumi airport.

Bus from Suvarnabhumi Airport to Jomtien Beach in Pattaya.

Our accommodation was near Jomtien beach, so I got off at the last stop, as the bus terminates at the Jomtien beach. Then I decided to walk towards my accommodation. I was using OsmAnd for navigation. However, the place was not marked on OpenStreetMap, and it turned out I missed the street my hostel was on and walked around 1 km further as I was chasing a similarly named incorrect hostel on OpenStreetMap. Then I asked for help from two men sitting at a caf . One of them said he will help me find the street my hostel is on. So, I walked with him, and he told me he lives in Thailand for many years, but he is from Kuwait. He also gave me valuable information. Like, he told me about shared hail-and-ride songthaews which run along the Jomtien Second Road and charge 10 Baht for any distance on their route. This tip significantly reduced our expenses. Further, he suggested me 7-Eleven shops for buying a local SIM. Like Malaysia, Thailand has 24/7 7-Eleven convenience stores, a lot of them not even 100 m apart. The Kuwaiti person dropped me at the address where my hostel was. I tried searching for a person in-charge of that hostel, and soon I realized there was no reception. After asking for help from locals for some time, I bumped into Fletcher, who also came to this address and was searching for the same. After finding a friend, I felt a sigh of relief. Adjacent to the property, there was a hairdresser shop. We went there and asked about this property. The woman called the owner, and she also told us the required passcodes to go inside. Our accommodation was in a room on the second floor, which required us to put a passcode for opening. We entered the passcode and entered the room. So, we stayed at this hostel which had no reception. Due to this, it took 2 hours to find our room and enter. It reminded me of a difficult experience I had in Albania, where me and Akshat were not able to find our apartment in one of the hottest days and the owner didn t know our language. Traveling from the place where the bus dropped me to the hostel, I saw streets were filled with bars and massage parlors, which was expected. Prostitutes were everywhere. We went out at night towards the beach and also roamed around in 7-Elevens to buy a SIM card for myself. I got a SIM for 7 day unlimited internet for 399 baht. Turns out that the rates of SIM cards at the airport were not so different from inside the city.

Road near Jomtien beach in Pattaya

Photo of a songthaew in Pattaya. There are shared songthaews which run along Jomtien Second road and takes 10 bath to anywhere on the route.

Jomtien Beach in Pattaya.

In terms of speaking English, locals didn t know English at all in both Pattaya and Bangkok. I normally don t expect locals to know English in a non-English speaking country, but the fact that Bangkok is one of the most visited places by tourists made me expect locals to know some English. Talking to locals is an integral part of travel for me, which I couldn t do a lot in Thailand. This aspect is much more important for me than going to touristy places. So, we were in Pattaya. Next morning, Fletcher and I went to Tiger park using shared songthaew. After that, we planned to visit Pattaya Floating market which is near the Tiger Park, but we felt the ticket prices were higher than it was worth. Fletcher had to leave for Bangkok on that day. I suggested him to go to Suvarnabhumi Airport from the Jomtien beach bus terminal (this was the route I took the last day in opposite direction) to avoid traffic congestion inside Bangkok, as he can follow up with metro once he reaches the airport. From the floating market, we were walking in sweltering heat to reach the Jomtien beach. I tried asking for a lift and eventually got successful as a scooty stopped, and surprisingly the person gave a ride to both of us. He was from Delhi, so maybe that s the reason he stopped for us. Then we took a songthaew to the bus terminal and after having lunch, Fletcher left for Bangkok.

A welcome sign at Pattaya Floating market.

This Korean Vegetasty noodles pack was yummy and was available at many 7-Eleven stores.

Next day I went to Bangkok, but Fletcher already left for Kuala Lumpur. Here I had booked a private room in a hotel (instead of a hostel) for four nights, mainly because of my luggage. This costed 5600 INR for four nights. It was 2 km from the metro station, which I used to walk both sides. In Bangkok, I visited Sukhumvit and Siam by metro. Going to some areas require crossing the Chao Phraya river. For this, I took Chao Phraya Express Boat for going to places like Khao San road and Wat Arun. I would recommend taking the boat ride as it had very good views. In Bangkok, I met a person from Pakistan staying in my hotel and so here also I got some company. But by the time I met him, my days were almost over. So, we went to a random restaurant selling Indian food where we ate some paneer dish with naan and that restaurant person was from Myanmar.

Wat Arun temple stamps your hand upon entry

Wat Arun temple

Khao San Road

A food stall at Khao San Road

Chao Phraya Express Boat

For eating, I mainly relied on fruits and convenience stores. Bananas were very tasty. This was the first time I saw banana flesh being yellow. Mangoes were delicious and pineapples were smaller and flavorful. I also ate Rose Apple, which I never had before. I had Chhole Kulche once in Sukhumvit. That was a little expensive as it costed 164 baht. I also used to buy premix coffee packets from 7-Eleven convenience stores and prepare them inside the stores.

Banana with yellow flesh

Fruits at a stall in Bangkok

Trimmed pineapples from Thailand.

Corn in Bangkok.

A board showing coffee menu at a 7-Eleven store along with rates in Pattaya.

In this section of 7-Eleven, you can buy a premix coffee and mix it with hot water provided at the store to prepare.

My booking from Bangkok to Delhi was in Air India flight, and they were serving alcohol in the flight. I chose red wine, and this was my first time having alcohol in a flight.

Red wine being served in Air India

Notes

• In this whole trip spanning two weeks, I did not pay for drinking water (except for once in Pattaya which was 9 baht) and toilets. Bangkok and Kuala Lumpur have plenty of malls where you should find a free-of-cost toilet nearby. For drinking water, I relied mainly on my accommodation providing refillable water for my bottle.
• Thailand seemed more expensive than Malaysia on average. Malaysia had discounted price due to the Chinese New year.
• I liked Pattaya more than Bangkok. Maybe because Pattaya has beach and Bangkok doesn t. Pattaya seemed more lively, and I could meet and talk to a few people as opposed to Bangkok.
• Chao Phraya River express boat costs 150 baht for one day where you can hop on and off to any boat.

My effort to improve transparency and confidence of public apt archives continues. I started to work on this in Apt Archive Transparency in which I mention the debdistget project in passing. Debdistget is responsible for mirroring index files for some public apt archives. I ve realized that having a publicly auditable and preserved mirror of the apt repositories is central to being able to do apt transparency work, so the debdistget project has become more central to my project than I thought. Currently I track Trisquel, PureOS, Gnuinos and their upstreams Ubuntu, Debian and Devuan. Debdistget download Release/Package/Sources files and store them in a git repository published on GitLab. Due to size constraints, it uses two repositories: one for the Release/InRelease files (which are small) and one that also include the Package/Sources files (which are large). See for example the repository for Trisquel release files and the Trisquel package/sources files. Repositories for all distributions can be found in debdistutils archives GitLab sub-group. The reason for splitting into two repositories was that the git repository for the combined files become large, and that some of my use-cases only needed the release files. Currently the repositories with packages (which contain a couple of months worth of data now) are 9GB for Ubuntu, 2.5GB for Trisquel/Debian/PureOS, 970MB for Devuan and 450MB for Gnuinos. The repository size is correlated to the size of the archive (for the initial import) plus the frequency and size of updates. Ubuntu s use of Apt Phased Updates (which triggers a higher churn of Packages file modifications) appears to be the primary reason for its larger size. Working with large Git repositories is inefficient and the GitLab CI/CD jobs generate quite some network traffic downloading the git repository over and over again. The most heavy user is the debdistdiff project that download all distribution package repositories to do diff operations on the package lists between distributions. The daily job takes around 80 minutes to run, with the majority of time is spent on downloading the archives. Yes I know I could look into runner-side caching but I dislike complexity caused by caching. Fortunately not all use-cases requires the package files. The debdistcanary project only needs the Release/InRelease files, in order to commit signatures to the Sigstore and Sigsum transparency logs. These jobs still run fairly quickly, but watching the repository size growth worries me. Currently these repositories are at Debian 440MB, PureOS 130MB, Ubuntu/Devuan 90MB, Trisquel 12MB, Gnuinos 2MB. Here I believe the main size correlation is update frequency, and Debian is large because I track the volatile unstable. So I hit a scalability end with my first approach. A couple of months ago I solved this by discarding and resetting these archival repositories. The GitLab CI/CD jobs were fast again and all was well. However this meant discarding precious historic information. A couple of days ago I was reaching the limits of practicality again, and started to explore ways to fix this. I like having data stored in git (it allows easy integration with software integrity tools such as GnuPG and Sigstore, and the git log provides a kind of temporal ordering of data), so it felt like giving up on nice properties to use a traditional database with on-disk approach. So I started to learn about Git-LFS and understanding that it was able to handle multi-GB worth of data that looked promising. Fairly quickly I scripted up a GitLab CI/CD job that incrementally update the Release/Package/Sources files in a git repository that uses Git-LFS to store all the files. The repository size is now at Ubuntu 650kb, Debian 300kb, Trisquel 50kb, Devuan 250kb, PureOS 172kb and Gnuinos 17kb. As can be expected, jobs are quick to clone the git archives: debdistdiff pipelines went from a run-time of 80 minutes down to 10 minutes which more reasonable correlate with the archive size and CPU run-time. The LFS storage size for those repositories are at Ubuntu 15GB, Debian 8GB, Trisquel 1.7GB, Devuan 1.1GB, PureOS/Gnuinos 420MB. This is for a couple of days worth of data. It seems native Git is better at compressing/deduplicating data than Git-LFS is: the combined size for Ubuntu is already 15GB for a couple of days data compared to 8GB for a couple of months worth of data with pure Git. This may be a sub-optimal implementation of Git-LFS in GitLab but it does worry me that this new approach will be difficult to scale too. At some level the difference is understandable, Git-LFS probably store two different Packages files around 90MB each for Trisquel as two 90MB files, but native Git would store it as one compressed version of the 90MB file and one relatively small patch to turn the old files into the next file. So the Git-LFS approach surprisingly scale less well for overall storage-size. Still, the original repository is much smaller, and you usually don t have to pull all LFS files anyway. So it is net win. Throughout this work, I kept thinking about how my approach relates to Debian s snapshot service. Ultimately what I would want is a combination of these two services. To have a good foundation to do transparency work I would want to have a collection of all Release/Packages/Sources files ever published, and ultimately also the source code and binaries. While it makes sense to start on the latest stable releases of distributions, this effort should scale backwards in time as well. For reproducing binaries from source code, I need to be able to securely find earlier versions of binary packages used for rebuilds. So I need to import all the Release/Packages/Sources packages from snapshot into my repositories. The latency to retrieve files from that server is slow so I haven t been able to find an efficient/parallelized way to download the files. If I m able to finish this, I would have confidence that my new Git-LFS based approach to store these files will scale over many years to come. This remains to be seen. Perhaps the repository has to be split up per release or per architecture or similar. Another factor is storage costs. While the git repository size for a Git-LFS based repository with files from several years may be possible to sustain, the Git-LFS storage size surely won t be. It seems GitLab charges the same for files in repositories and in Git-LFS, and it is around $500 per 100GB per year. It may be possible to setup a separate Git-LFS backend not hosted at GitLab to serve the LFS files. Does anyone know of a suitable server implementation for this? I had a quick look at the Git-LFS implementation list and it seems the closest reasonable approach would be to setup the Gitea-clone Forgejo as a self-hosted server. Perhaps a cloud storage approach a la S3 is the way to go? The cost to host this on GitLab will be manageable for up to ~1TB ($5000/year) but scaling it to storing say 500TB of data would mean an yearly fee of $2.5M which seems like poor value for the money. I realized that ultimately I would want a git repository locally with the entire content of all apt archives, including their binary and source packages, ever published. The storage requirements for a service like snapshot (~300TB of data?) is today not prohibitly expensive: 20TB disks are $500 a piece, so a storage enclosure with 36 disks would be around $18.000 for 720TB and using RAID1 means 360TB which is a good start. While I have heard about ~TB-sized Git-LFS repositories, would Git-LFS scale to 1PB? Perhaps the size of a git repository with multi-millions number of Git-LFS pointer files will become unmanageable? To get started on this approach, I decided to import a mirror of Debian s bookworm for amd64 into a Git-LFS repository. That is around 175GB so reasonable cheap to host even on GitLab ($1000/year for 200GB). Having this repository publicly available will make it possible to write software that uses this approach (e.g., porting debdistreproduce), to find out if this is useful and if it could scale. Distributing the apt repository via Git-LFS would also enable other interesting ideas to protecting the data. Consider configuring apt to use a local file:// URL to this git repository, and verifying the git checkout using some method similar to Guix s approach to trusting git content or Sigstore s gitsign. A naive push of the 175GB archive in a single git commit ran into pack size limitations: remote: fatal: pack exceeds maximum allowed size (4.88 GiB) however breaking up the commit into smaller commits for parts of the archive made it possible to push the entire archive. Here are the commands to create this repository: git init
git lfs install
git lfs track 'dists/**' 'pool/**'
git add .gitattributes
git commit -m"Add Git-LFS track attributes." .gitattributes
time debmirror --method=rsync --host ftp.se.debian.org --root :debian --arch=amd64 --source --dist=bookworm,bookworm-updates --section=main --verbose --diff=none --keyring /usr/share/keyrings/debian-archive-keyring.gpg --ignore .git .
git add dists project
git commit -m"Add." -a
git remote add origin git@gitlab.com:debdistutils/archives/debian/mirror.git
git push --set-upstream origin --all
for d in pool//; do
echo $d;
time git add $d;
git commit -m"Add $d." -a
git push
done The resulting repository size is around 27MB with Git LFS object storage around 174GB. I think this approach would scale to handle all architectures for one release, but working with a single git repository for all releases for all architectures may lead to a too large git repository (>1GB). So maybe one repository per release? These repositories could also be split up on a subset of pool/ files, or there could be one repository per release per architecture or sources. Finally, I have concerns about using SHA1 for identifying objects. It seems both Git and Debian s snapshot service is currently using SHA1. For Git there is SHA-256 transition and it seems GitLab is working on support for SHA256-based repositories. For serious long-term deployment of these concepts, it would be nice to go for SHA256 identifiers directly. Git-LFS already uses SHA256 but Git internally uses SHA1 as does the Debian snapshot service. What do you think? Happy Hacking!

Release 0.6.35 of the digest package arrived at CRAN today and has also been uploaded to Debian already. digest creates hash digests of arbitrary R objects. It can use a number different hashing algorithms (md5, sha-1, sha-256, sha-512, crc32, xxhash32, xxhash64, murmur32, spookyhash, blake3,crc32c and now also xxh3_64 and xxh3_128), and enables easy comparison of (potentially large and nested) R language objects as it relies on the native serialization in R. It is a mature and widely-used package (with 65.8 million downloads just on the partial cloud mirrors of CRAN which keep logs) as many tasks may involve caching of objects for which it provides convenient general-purpose hash key generation to quickly identify the various objects. This release updates the included xxHash version to the current verion 0.8.2 updating the existing xxhash32 and xxhash64 hash functions and also adding the newer xxh3_64 and xxh3_128 ones. We have a project at work using xxh3_128 from Python which made me realize having it from R would be nice too, and given the existing infrastructure in the package actually doing so was fairly quick and straightforward. My CRANberries provides a summary of changes to the previous version. For questions or comments use the issue tracker off the GitHub repo. For documentation (including the changelog) see the documentation site. If you like this or other open-source work I do, you can now 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.

A first maintenance of the still fairly new package tinythemes arrived on CRAN today. tinythemes provides the theme_ipsum_rc() function from hrbrthemes by Bob Rudis in a zero (added) dependency way. A simple example is (also available as a demo inside the package) contrasts the default style (on left) with the one added by this package (on the right): This version mostly just updates to the newest releases of ggplot2 as one must, and takes advantage of Bob s update to hrbrthemes yesterday. The full set of changes since the initial CRAN release follows.

Changes in spdl version 0.0.2 (2024-03-04)

• Added continuous integrations action based on r2u
• Added demo/ directory and a READNE.md
• Minor edits to help page content
• Synchronised with ggplot2 3.5.0 via hrbrthemes

Courtesy of my CRANberries, there is a diffstat report relative to previous release. More detailed information is on the repo where comments and suggestions are welcome. 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.

Two months into my new gig and it s going great! Tracking my time has taken a bit of getting used to, but having something that amounts to a queryable database of everything I ve done has also allowed some helpful introspection. Freexian sponsors up to 20% of my time on Debian tasks of my choice. In fact I ve been spending the bulk of my time on debusine which is itself intended to accelerate work on Debian, but more details on that later. While I contribute to Freexian s summaries now, I ve also decided to start writing monthly posts about my free software activity as many others do, to get into some more detail. January 2024

• I added Incus support to autopkgtest. Incus is a system container and virtual machine manager, forked from Canonical s LXD. I switched my laptop over to it and then quickly found that it was inconvenient not to be able to run Debian package test suites using autopkgtest, so I tweaked autopkgtest s existing LXD integration to support using either LXD or Incus.
• I discovered Perl::Critic and used it to tidy up some poor practices in several of my packages, including debconf. Perl used to be my language of choice but I ve been mostly using Python for over a decade now, so I m not as fluent as I used to be and some mechanical assistance with spotting common errors is helpful; besides, I m generally a big fan of applying static analysis to everything possible in the hope of reducing bug density. Of course, this did result in a couple of regressions (1, 2), but at least we caught them fairly quickly.
• I did some overdue debconf maintenance, mainly around tidying up error message handling in several places (1, 2, 3).
• I did some routine maintenance to move several of my upstream projects to a new Gnulib stable branch.
• debmirror includes a useful summary of how big a Debian mirror is, but it hadn t been updated since 2010 and the script to do so had bitrotted quite badly. I fixed that and added a recurring task for myself to refresh this every six months.

February 2024

• Some time back I added AppArmor and seccomp confinement to man-db. This was mainly motivated by a desire to support manual pages in snaps (which is still open several years later ), but since reading manual pages involves a non-trivial text processing toolchain mostly written in C++, I thought it was reasonable to assume that some day it might have a vulnerability even though its track record has been good; so man now restricts the system calls that groff can execute and the parts of the file system that it can access. I stand by this, but it did cause some problems that have needed a succession of small fixes over the years. This month I issued DLA-3731-1, backporting some of those fixes to buster.
• I spent some time chasing a console-setup build failure following the removal of kFreeBSD support, which was uploaded by mistake. I suggested a set of fixes for this, but the author of the change to remove kFreeBSD support decided to take a different approach (fair enough), so I ve abandoned this.
• I updated the Debian zope.testrunner package to 6.3.1.
• openssh:
  • A Freexian collaborator had a problem with automating installations involving changes to /etc/ssh/sshd_config. This turned out to be resolvable without any changes, but in the process of investigating I noticed that my dodgy arrangements to avoid ucf prompts in certain cases had bitrotted slightly, which meant that some people might be prompted unnecessarily. I fixed this and arranged for it not to happen again.
  • Following a recent debian-devel discussion, I realized that some particularly awkward code in the OpenSSH packaging was now obsolete, and removed it.
• I backported a python-channels-redis fix to bookworm. I wasn t the first person to run into this, but I rediscovered it while working on debusine and it was confusing enough that it seemed worth fixing in stable.
• I fixed a simple build failure in storm.
• I dug into a very confusing cluster of celery build failures (1, 2, 3), and tracked the hardest bit down to a Python 3.12 regression, now fixed in unstable thanks to Stefano Rivera. Getting celery back into testing is blocked on the 64-bit time_t transition for now, but once that s out of the way it should flow smoothly again.

Last month, I had a trip to Malaysia and Thailand. I stayed for six days in each of the countries. The selection of these countries was due to both of them granting visa-free entry to Indian tourists for some time window. This post covers the Malaysia part and Thailand part will be covered in the next post. If you want to travel to any of these countries in the visa-free time period, I have written all the questions asked during immigration and at airports during this trip here which might be of help. I mostly stayed in Kuala Lumpur and went to places around it. Although before the trip, I planned to visit Ipoh and Cameron Highlands too, but could not cover it during the trip. I found planning a trip to Malaysia a little difficult. The country is divided into two main islands - Peninsular Malaysia and Borneo. Then there are more islands - Langkawi, Penang island, Perhentian and Redang Islands. Reaching those islands seemed a little difficult to plan and I wish to visit more places in my next Malaysia trip. My first day hostel was booked in Chinatown part of Kuala Lumpur, near Pasar Seni LRT station. As soon as I checked-in and entered my room, I met another Indian named Fletcher, and after that we accompanied each other in the trip. That day, we went to Muzium Negara and Little India. I realized that if you know the right places to buy what you want, Malaysia could be quite cheap. Malaysian currency is Malaysian Ringgit (MYR). 1 MYR is equal to 18 INR. For 2 MYR, you can get a good masala tea in Little India and it costs like 4-5 MYR for a masala dosa. The vegetarian food has good availability in Kuala Lumpur, thanks to the Tamil community. I also tried Mee Goreng, which was vegetarian, and I found it fine in terms of taste. When I checked about Mee Goreng on Wikipedia, I found out that it is unique to Indian immigrants in Malaysia (and neighboring countries) but you don t get it in India!

Mee Goreng, a dish made of noodles in Malaysia.

For the next day, Fletcher had planned a trip to Genting Highlands and pre booked everything. I also planned to join him but when we went to KL Sentral to take the bus, his bus tickets were sold out. I could take a bus at a different time, but decided to visit some other place for the day and cover Genting Highlands later. At the ticket counter, I met a family from Delhi and they wanted to go to Genting Highlands but due to not getting bus tickets for that day, they decided to buy a ticket for the next day and instead planned for Batu Caves that day. I joined them and went to Batu Caves. After returning from Batu Caves, we went our separate ways. I went back and took rest at my hostel and later went to Petronas Towers at night. Petronas Towers is the icon of Kuala Lumpur. Having a photo there was a must. I was at Petronas Towers at around 9 PM. Around that time, Fletcher came back from Genting Highlands and we planned to meet at KL Sentral to head for dinner.

Me at Petronas Towers.

We went back to the same place as the day before where I had Mee Goreng. This time we had dosa and a masala tea. Their masala tea from the last day was tasty and that s why I was looking for them in the first place. We also met a Malaysian family having Indian ancestry dining there and had a nice conversation. Then we went to a place to eat roti canai in Pasar Seni market. Roti canai is a popular non-vegetarian dish in Malaysia but I took the vegetarian version.

Photo with Malaysians.

The next day, we went to Berjaya Time Square shopping place which sells pretty cheap items for daily use and souveniers too. However, I bought souveniers from Petaling Street, which is in Chinatown. At night, we explored Bukit Bintang, which is the heart of Kuala Lumpur and is famous for its nightlife. After that, Fletcher went to Bangkok and I was in Malaysia for two more days. Next day, I went to Genting Highlands and took the cable car, which had awesome views. I came back to Kuala Lumpur by the night. The remaining day I just roamed around in Bukit Bintang. Then I took a flight for Bangkok on 7th Feb, which I will cover in the next post. In Malaysia, I met so many people from different countries - apart from people from Indian subcontinent, I met Syrians, Indonesians (Malaysia seems to be a popular destination for Indonesian tourists) and Burmese people. Meeting people from other cultures is an integral part of travel for me. My expenses for Food + Accommodation + Travel added to 10,000 INR for a week in Malaysia, while flight costs were: 13,000 INR (Delhi to Kuala Lumpur) + 10,000 INR (Kuala Lumpur to Bangkok) + 12,000 INR (Bangkok to Delhi). For OpenStreetMap users, good news is Kuala Lumpur is fairly well-mapped on OpenStreetMap.

Tips

• I bought local SIM from a shop at KL Sentral station complex which had news in their name (I forgot the exact name and there are two shops having news in their name) and it was the cheapest option I could find. The SIM was 10 MYR for 5 GB data for a week. If you want to make calls too, then you need to spend extra 5 MYR.
• 7-Eleven and KK Mart convenience stores are everywhere in the city and they are open all the time (24 hours a day). If you are a vegetarian, you can at least get some bread and cheese from there to eat.
• A lot of people know English (and many - Indians, Pakistanis, Nepalis - know Hindi) in Kuala Lumpur, so I had no language problems most of the time.
• For shopping on budget, you can go to Petaling Street, Berjaya Time Square or Bukit Bintang. In particular, there is a shop named I Love KL Gifts in Bukit Bintang which had very good prices. just near the metro/monorail stattion. Check out location of the shop on OpenStreetMap.

This is my third update on writing a language server for Debian packaging files, which aims at providing a better developer experience for Debian packagers. Lets go over what have done since the last report.

I have spent some more time on improving my language server for debian/control. Today, I managed to provide the following features:

• The X- style prefixes for field names are now understood and handled. This means the language server now considers XC-Package-Type the same as Package-Type.

• More diagnostics:

  • Fields without values now trigger an error marker
  • Duplicated fields now trigger an error marker
  • Fields used in the wrong paragraph now trigger an error marker
  • Typos in field names or values now trigger a warning marker. For field names, X- style prefixes are stripped before typo detection is done.
  • The value of the Section field is now validated against a dataset of known sections and trigger a warning marker if not known.

• The "on-save trim end of line whitespace" now works. I had a logic bug in the server side code that made it submit "no change" edits to the editor.

• The language server now provides "hover" documentation for field names. There is a small screenshot of this below. Sadly, emacs does not support markdown or, if it does, it does not announce the support for markdown. For now, all the documentation is always in markdown format and the language server will tag it as either markdown or plaintext depending on the announced support.

• The language server now provides quick fixes for some of the more trivial problems such as deprecated fields or typos of fields and values.

• Added more known fields including the XS-Autobuild field for non-free packages along with a link to the relevant devref section in its hover doc.

This covers basically all my known omissions from last update except spellchecking of the Description field.

It's been a LONG day: two point releases in a day takes of the order of twelve or thirteen hours of fairly solid work on behalf of those doing the releases and testing.Thanks firstly to the main Debian release team for all the initial work.Thanks to Isy, RattusRattus, Sledge and egw in Cottenham, smcv and Helen closer to the centre of Cambridge, cacin and others who have dropped in and out of IRC and helped testing.

I've been at home but active on IRC - missing the team (and the food) and drinking far too much coffee/eating too many biscuits.

We've found relatively few bugs that we haven't previously noted: it's been a good day. Back again, at some point a couple of months from now to do this all over again.With luck, I can embed a picture of the Cottenham folk below: it's fun to know _exactly_ where people are because you've been there yourself.

If you ve perused the ActivityPub feed of certificates whose keys are known to be compromised, and clicked on the Show More button to see the name of the certificate issuer, you may have noticed that some issuers seem to come up again and again. This might make sense after all, if a CA is issuing a large volume of certificates, they ll be seen more often in a list of compromised certificates. In an attempt to see if there is anything that we can learn from this data, though, I did a bit of digging, and came up with some illuminating results.

The Procedure I started off by finding all the unexpired certificates logged in Certificate Transparency (CT) logs that have a key that is in the pwnedkeys database as having been publicly disclosed. From this list of certificates, I removed duplicates by matching up issuer/serial number tuples, and then reduced the set by counting the number of unique certificates by their issuer. This gave me a list of the issuers of these certificates, which looks a bit like this:

/C=BE/O=GlobalSign nv-sa/CN=AlphaSSL CA - SHA256 - G4
/C=GB/ST=Greater Manchester/L=Salford/O=Sectigo Limited/CN=Sectigo RSA Domain Validation Secure Server CA
/C=GB/ST=Greater Manchester/L=Salford/O=Sectigo Limited/CN=Sectigo RSA Organization Validation Secure Server CA
/C=US/ST=Arizona/L=Scottsdale/O=GoDaddy.com, Inc./OU=http://certs.godaddy.com/repository//CN=Go Daddy Secure Certificate Authority - G2
/C=US/ST=Arizona/L=Scottsdale/O=Starfield Technologies, Inc./OU=http://certs.starfieldtech.com/repository//CN=Starfield Secure Certificate Authority - G2
/C=AT/O=ZeroSSL/CN=ZeroSSL RSA Domain Secure Site CA
/C=BE/O=GlobalSign nv-sa/CN=GlobalSign GCC R3 DV TLS CA 2020

Rather than try to work with raw issuers (because, as Andrew Ayer says, The SSL Certificate Issuer Field is a Lie), I mapped these issuers to the organisations that manage them, and summed the counts for those grouped issuers together.

The Data

Insert obligatory "not THAT data" comment here

The end result of this work is the following table, sorted by the count of certificates which have been compromised by exposing their private key:

Issuer	Compromised Count
Sectigo	170
ISRG (Let's Encrypt)	161
GoDaddy	141
DigiCert	81
GlobalSign	46
Entrust	3
SSL.com	1

If you re familiar with the CA ecosystem, you ll probably recognise that the organisations with large numbers of compromised certificates are also those who issue a lot of certificates. So far, nothing particularly surprising, then. Let s look more closely at the relationships, though, to see if we can get more useful insights.

Volume Control Using the issuance volume report from crt.sh, we can compare issuance volumes to compromise counts, to come up with a compromise rate . I m using the Unexpired Precertificates colume from the issuance volume report, as I feel that s the number that best matches the certificate population I m examining to find compromised certificates. To maintain parity with the previous table, this one is still sorted by the count of certificates that have been compromised.

Issuer	Issuance Volume	Compromised Count	Compromise Rate
Sectigo	88,323,068	170	1 in 519,547
ISRG (Let's Encrypt)	315,476,402	161	1 in 1,959,480
GoDaddy	56,121,429	141	1 in 398,024
DigiCert	144,713,475	81	1 in 1,786,586
GlobalSign	1,438,485	46	1 in 31,271
Entrust	23,166	3	1 in 7,722
SSL.com	171,816	1	1 in 171,816

If we now sort this table by compromise rate, we can see which organisations have the most (and least) leakiness going on from their customers:

Issuer	Issuance Volume	Compromised Count	Compromise Rate
Entrust	23,166	3	1 in 7,722
GlobalSign	1,438,485	46	1 in 31,271
SSL.com	171,816	1	1 in 171,816
GoDaddy	56,121,429	141	1 in 398,024
Sectigo	88,323,068	170	1 in 519,547
DigiCert	144,713,475	81	1 in 1,786,586
ISRG (Let's Encrypt)	315,476,402	161	1 in 1,959,480

By grouping by order-of-magnitude in the compromise rate, we can identify three bands :

• The Super Leakers: Customers of Entrust and GlobalSign seem to love to lose control of their private keys. For Entrust, at least, though, the small volumes involved make the numbers somewhat untrustworthy. The three compromised certificates could very well belong to just one customer, for instance. I m not aware of anything that GlobalSign does that would make them such an outlier, either, so I m inclined to think they just got unlucky with one or two customers, but as CAs don t include customer IDs in the certificates they issue, it s not possible to say whether that s the actual cause or not.
• The Regular Leakers: Customers of SSL.com, GoDaddy, and Sectigo all have compromise rates in the 1-in-hundreds-of-thousands range. Again, the low volumes of SSL.com make the numbers somewhat unreliable, but the other two organisations in this group have large enough numbers that we can rely on that data fairly well, I think.
• The Low Leakers: Customers of DigiCert and Let s Encrypt are at least three times less likely than customers of the regular leakers to lose control of their private keys. Good for them!

Now we have some useful insights we can think about.

Why Is It So?

If you don't know who Professor Julius Sumner Miller is, I highly recommend finding out

All of the organisations on the list, with the exception of Let s Encrypt, are what one might term traditional CAs. To a first approximation, it s reasonable to assume that the vast majority of the customers of these traditional CAs probably manage their certificates the same way they have for the past two decades or more. That is, they generate a key and CSR, upload the CSR to the CA to get a certificate, then copy the cert and key somewhere. Since humans are handling the keys, there s a higher risk of the humans using either risky practices, or making a mistake, and exposing the private key to the world. Let s Encrypt, on the other hand, issues all of its certificates using the ACME (Automatic Certificate Management Environment) protocol, and all of the Let s Encrypt documentation encourages the use of software tools to generate keys, issue certificates, and install them for use. Given that Let s Encrypt has 161 compromised certificates currently in the wild, it s clear that the automation in use is far from perfect, but the significantly lower compromise rate suggests to me that lifecycle automation at least reduces the rate of key compromise, even though it doesn t eliminate it completely.

Sidebar: ACME Does Not Currently Rule The World It is true that all of the organisations in this analysis also provide ACME issuance workflows, should customers desire it. However, the traditional CA companies have been around a lot longer than ACME has, and so they probably acquired many of their customers before ACME existed. Given that it s incredibly hard to get humans to change the way they do things, once they have a way that works , it seems reasonable to assume that most of the certificates issued by these CAs are handled in the same human-centric, error-prone manner they always have been. If organisations would like to refute this assumption, though, by sharing their data on ACME vs legacy issuance rates, I m sure we d all be extremely interested.

Explaining the Outlier The difference in presumed issuance practices would seem to explain the significant difference in compromise rates between Let s Encrypt and the other organisations, if it weren t for one outlier. This is a largely traditional CA, with the manual-handling issues that implies, but with a compromise rate close to that of Let s Encrypt. We are, of course, talking about DigiCert. The thing about DigiCert, that doesn t show up in the raw numbers from crt.sh, is that DigiCert manages the issuance of certificates for several of the biggest hosted TLS providers, such as CloudFlare and AWS. When these services obtain a certificate from DigiCert on their customer s behalf, the private key is kept locked away, and no human can (we hope) get access to the private key. This is supported by the fact that no certificates identifiably issued to either CloudFlare or AWS appear in the set of certificates with compromised keys. When we ask for all certificates issued by DigiCert , we get both the certificates issued to these big providers, which are very good at keeping their keys under control, as well as the certificates issued to everyone else, whose key handling practices may not be quite so stringent. It s possible, though not trivial, to account for certificates issued to these hosted TLS providers, because the certificates they use are issued from intermediates branded to those companies. With the crt.sh psql interface we can run this query to get the total number of unexpired precertificates issued to these managed services:

SELECT SUM(sub.NUM_ISSUED[2] - sub.NUM_EXPIRED[2])
  FROM (
    SELECT ca.name, max(coalesce(coalesce(nullif(trim(cc.SUBORDINATE_CA_OWNER), ''), nullif(trim(cc.CA_OWNER), '')), cc.INCLUDED_CERTIFICATE_OWNER)) as OWNER,
           ca.NUM_ISSUED, ca.NUM_EXPIRED
      FROM ccadb_certificate cc, ca_certificate cac, ca
     WHERE cc.CERTIFICATE_ID = cac.CERTIFICATE_ID
       AND cac.CA_ID = ca.ID
  GROUP BY ca.ID
  ) sub
 WHERE sub.name ILIKE '%Amazon%' OR sub.name ILIKE '%CloudFlare%' AND sub.owner = 'DigiCert';

The number I get from running that query is 104,316,112, which should be subtracted from DigiCert s total issuance figures to get a more accurate view of what DigiCert s regular customers do with their private keys. When I do this, the compromise rates table, sorted by the compromise rate, looks like this:

Issuer	Issuance Volume	Compromised Count	Compromise Rate
Entrust	23,166	3	1 in 7,722
GlobalSign	1,438,485	46	1 in 31,271
SSL.com	171,816	1	1 in 171,816
GoDaddy	56,121,429	141	1 in 398,024
"Regular" DigiCert	40,397,363	81	1 in 498,732
Sectigo	88,323,068	170	1 in 519,547
All DigiCert	144,713,475	81	1 in 1,786,586
ISRG (Let's Encrypt)	315,476,402	161	1 in 1,959,480

In short, it appears that DigiCert s regular customers are just as likely as GoDaddy or Sectigo customers to expose their private keys.

What Does It All Mean? The takeaway from all this is fairly straightforward, and not overly surprising, I believe.

The less humans have to do with certificate issuance, the less likely they are to compromise that certificate by exposing the private key. While it may not be surprising, it is nice to have some empirical evidence to back up the common wisdom. Fully-managed TLS providers, such as CloudFlare, AWS Certificate Manager, and whatever Azure s thing is called, is the platonic ideal of this principle: never give humans any opportunity to expose a private key. I m not saying you should use one of these providers, but the security approach they have adopted appears to be the optimal one, and should be emulated universally. The ACME protocol is the next best, in that there are a variety of standardised tools widely available that allow humans to take themselves out of the loop, but it s still possible for humans to handle (and mistakenly expose) key material if they try hard enough. Legacy issuance methods, which either cannot be automated, or require custom, per-provider automation to be developed, appear to be at least four times less helpful to the goal of avoiding compromise of the private key associated with a certificate.

Humans Are, Of Course, The Problem

No thanks, Bender, I'm busy tonight

This observation that if you don t let humans near keys, they don t get leaked is further supported by considering the biggest issuers by volume who have not issued any certificates whose keys have been compromised: Google Trust Services (fourth largest issuer overall, with 57,084,529 unexpired precertificates), and Microsoft Corporation (sixth largest issuer overall, with 22,852,468 unexpired precertificates). It appears that somewhere between most and basically all of the certificates these organisations issue are to customers of their public clouds, and my understanding is that the keys for these certificates are managed in same manner as CloudFlare and AWS the keys are locked away where humans can t get to them. It should, of course, go without saying that if a human can never have access to a private key, it makes it rather difficult for a human to expose it. More broadly, if you are building something that handles sensitive or secret data, the more you can do to keep humans out of the loop, the better everything will be.

Your Support is Appreciated If you d like to see more analysis of how key compromise happens, and the lessons we can learn from examining billions of certificates, please show your support by buying me a refreshing beverage. Trawling CT logs is thirsty work.

Appendix: Methodology Limitations In the interests of clarity, I feel it s important to describe ways in which my research might be flawed. Here are the things I know of that may have impacted the accuracy, that I couldn t feasibly account for.

• Time Periods: Because time never stops, there is likely to be some slight mismatches in the numbers obtained from the various data sources, because they weren t collected at exactly the same moment.
• Issuer-to-Organisation Mapping: It s possible that the way I mapped issuers to organisations doesn t match exactly with how crt.sh does it, meaning that counts might be skewed. I tried to minimise that by using the same data sources (the CCADB AllCertificates report) that I believe that crt.sh uses for its mapping, but I cannot be certain of a perfect match.
• Unwarranted Grouping: I ve drawn some conclusions about the practices of the various organisations based on their general approach to certificate issuance. If a particular subordinate CA that I ve grouped into the parent organisation is managed in some unusual way, that might cause my conclusions to be erroneous. I was able to fairly easily separate out CloudFlare, AWS, and Azure, but there are almost certainly others that I didn t spot, because hoo boy there are a lot of intermediate CAs out there.

Review: Bluebird, by Ciel Pierlot

Publisher:	Angry Robot
Copyright:	2022
ISBN:	0-85766-967-2
Format:	Kindle
Pages:	458

Bluebird is a stand-alone far-future science fiction adventure. Ten thousand years ago, a star fell into the galaxy carrying three factions of humanity. The Ascetics, the Ossuary, and the Pyrites each believe that only their god survived and the other two factions are heretics. Between them, they have conquered the rest of the galaxy and its non-human species. The only thing the factions hate worse than each other are those who attempt to stay outside the faction system. Rig used to be a Pyrite weapon designer before she set fire to her office and escaped with her greatest invention. Now she's a Nightbird, a member of an outlaw band that tries to help refugees and protect her fellow Kashrini against Pyrite genocide. On her side, she has her girlfriend, an Ascetic librarian; her ship, Bluebird; and her guns, Panache and Pizzazz. And now, perhaps, the mysterious Ginka, a Zazra empath and remarkably capable fighter who helps Rig escape from an ambush by Pyrite soldiers. Rig wants to stay alive, help her people, and defy the factions. Pyrite wants Rig's secrets and, as leverage, has her sister. What Ginka wants is not entirely clear even to Ginka. This book is absurd, but I still had fun with it. It's dangerous for me to compare things to anime given how little anime that I've watched, but Bluebird had that vibe for me: anime, or maybe Japanese RPGs or superhero comics. The storytelling is very visual, combat-oriented, and not particularly realistic. Rig is a pistol sharpshooter and Ginka is the type of undefined deadly acrobatic fighter so often seen in that type of media. In addition to her ship, Rig has a gorgeous hand-maintained racing hoverbike with a beautiful paint job. It's that sort of book. It's also the sort of book where the characters obey cinematic logic designed to maximize dramatic physical confrontations, even if their actions make no logical sense. There is no facial recognition or screening, and it's bizarrely easy for the protagonists to end up in same physical location as high-up bad guys. One of the weapon systems that's critical to the plot makes no sense whatsoever. At critical moments, the bad guys behave more like final bosses in a video game, picking up weapons to deal with the protagonists directly instead of using their supposedly vast armies of agents. There is supposedly a whole galaxy full of civilizations with capital worlds covered in planet-spanning cities, but politics barely exist and the faction leaders get directly involved in the plot. If you are looking for a realistic projection of technology or society, I cannot stress enough that this is not the book that you're looking for. You probably figured that out when I mentioned ten thousand years of war, but that will only be the beginning of the suspension of disbelief problems. You need to turn off your brain and enjoy the action sequences and melodrama. I'm normally good at that, and I admit I still struggled because the plot logic is such a mismatch with the typical novels I read. There are several points where the characters do something that seems so monumentally dumb that I was sure Pierlot was setting them up for a fall, and then I got wrong-footed because their plan worked fine, or exploded for unrelated reasons. I think this type of story, heavy on dramatic eye-candy and emotional moments with swelling soundtracks, is a lot easier to pull off in visual media where all the pretty pictures distract your brain. In a novel, there's a lot of time to think about the strategy, technology, and government structure, which for this book is not a good idea. If you can get past that, though, Rig is entertainingly snarky and Ginka, who turns out to be the emotional heart of the book, is an enjoyable character with a real growth arc. Her background is a bit simplistic and the villains are the sort of pure evil that you might expect from this type of cinematic plot, but I cared about the outcome of her story. Some parts of the plot dragged and I think the editing could have been tighter, but there was enough competence porn and banter to pull me through. I would recommend Bluebird only cautiously, since you're going to need to turn off large portions of your brain and be in the right mood for nonsensically dramatic confrontations, but I don't regret reading it. It's mostly in primary colors and the emotional conflicts are not what anyone would call subtle, but it delivers a character arc and a somewhat satisfying ending. Content warning: There is a lot of serious physical injury in this book, including surgical maiming. If that's going to bother you, you may want to give this one a pass. Rating: 6 out of 10

The x13binary team is thrilled to share the availability of Release 1.1.60-1 of the x13binary package providing the X-13ARIMA-SEATS program by the US Census Bureau which arrived on CRAN earlier today. This release brings the package up to speed with the most current release by the Census Bureau. More importantly, we finally made good on an old promise to ourselves and now install the binary by compiling from its Fortran sources! No more pre-made binaries. This required some work by Kirill, Michael, and Jeroen to finalize matter because, as we all know, the CRAN build processes and tool chains can be a little byzantine in their details. Use on platforms not covered by binaries from CRAN (or r-universe) should just work too as the demands on the (Fortran) compiler are fairly standard. All in all the build is fairly lightweight and quick even when rebuilding from source. Courtesy of my CRANberries, there is also a diffstat report for this release showing changes to the previous release. 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.

While working on hz.tools, I started to move my beamforming code from 2-D (meaning, beamforming to some specific angle on the X-Y plane for waves on the X-Y plane) to 3-D. I ll have more to say about that once I get around to publishing the code as soon as I m sure it s not completely wrong, but in the meantime I decided to write a simple simulator to visually check the beamformer against the textbooks. The results were pretty rad, so I figured I d throw together a post since it s interesting all on its own outside of beamforming as a general topic. I figured I d write this in Rust, since I ve been using Rust as my primary language over at zoo, and it s a good chance to learn the language better. This post won t cover the basics of how phased arrays work or the specifics of calculating the phase offsets for each antenna, but I ll dig into how I wrote a simple simulator and how I wound up checking my phase offsets to generate the renders below.

Assumptions I didn t want to build a general purpose RF simulator, anything particularly generic, or something that would solve for any more than the things right in front of me. To do this as simply (and quickly all this code took about a day to write, including the beamforming math) I had to reduce the amount of work in front of me. Given that I was concerend with visualizing what the antenna pattern would look like in 3-D given some antenna geometry, operating frequency and configured beam, I made the following assumptions: All anetnnas are perfectly isotropic they receive a signal that is exactly the same strength no matter what direction the signal originates from. There s a single point-source isotropic emitter in the far-field (I modeled this as being 1 million meters away 1000 kilometers) of the antenna system. There is no noise, multipath, loss or distortion in the signal as it travels through space. Antennas will never interfere with each other.

2-D Polar Plots The last time I wrote something like this, I generated 2-D GIFs which show a radiation pattern, not unlike the polar plots you d see on a microphone. These are handy because it lets you visualize what the directionality of the antenna looks like, as well as in what direction emissions are captured, and in what directions emissions are nulled out. You can see these plots on spec sheets for antennas in both 2-D and 3-D form. Now, let s port the 2-D approach to 3-D and see how well it works out.

Writing the 3-D simulator As an EM wave travels through free space, the place at which you sample the wave controls that phase you observe at each time-step. This means, assuming perfectly synchronized clocks, a transmitter and receiver exactly one RF wavelength apart will observe a signal in-phase, but a transmitter and receiver a half wavelength apart will observe a signal 180 degrees out of phase. This means that if we take the distance between our point-source and antenna element, divide it by the wavelength, we can use the fractional part of the resulting number to determine the phase observed. If we multiply that number (in the range of 0 to just under 1) by tau, we can generate a complex number by taking the cos and sin of the multiplied phase (in the range of 0 to tau), assuming the transmitter is emitting a carrier wave at a static amplitude and all clocks are in perfect sync.

 let observed_phases: Vec<Complex> = antennas
.iter()
.map( antenna   
let distance = (antenna - tx).magnitude();
let distance = distance - (distance as i64 as f64);
((distance / wavelength) * TAU)
 )
.map( phase  Complex(phase.cos(), phase.sin()))
.collect();

At this point, given some synthetic transmission point and each antenna, we know what the expected complex sample would be at each antenna. At this point, we can adjust the phase of each antenna according to the beamforming phase offset configuration, and add up every sample in order to determine what the entire system would collectively produce a sample as.

 let beamformed_phases: Vec<Complex> = ...;
let magnitude = beamformed_phases
.iter()
.zip(observed_phases.iter())
.map( (beamformed, observed)  observed * beamformed)
.reduce( acc, el  acc + el)
.unwrap()
.abs();

Armed with this information, it s straight forward to generate some number of (Azimuth, Elevation) points to sample, generate a transmission point far away in that direction, resolve what the resulting Complex sample would be, take its magnitude, and use that to create an (x, y, z) point at (azimuth, elevation, magnitude). The color attached two that point is based on its distance from (0, 0, 0). I opted to use the Life Aquatic table for this one. After this process is complete, I have a point cloud of ((x, y, z), (r, g, b)) points. I wrote a small program using kiss3d to render point cloud using tons of small spheres, and write out the frames to a set of PNGs, which get compiled into a GIF. Now for the fun part, let s take a look at some radiation patterns!

1x4 Phased Array The first configuration is a phased array where all the elements are in perfect alignment on the y and z axis, and separated by some offset in the x axis. This configuration can sweep 180 degrees (not the full 360), but can t be steared in elevation at all. Let s take a look at what this looks like for a well constructed 1x4 phased array: And now let s take a look at the renders as we play with the configuration of this array and make sure things look right. Our initial quarter-wavelength spacing is very effective and has some outstanding performance characteristics. Let s check to see that everything looks right as a first test. Nice. Looks perfect. When pointing forward at (0, 0), we d expect to see a torus, which we do. As we sweep between 0 and 360, astute observers will notice the pattern is mirrored along the axis of the antennas, when the beam is facing forward to 0 degrees, it ll also receive at 180 degrees just as strong. There s a small sidelobe that forms when it s configured along the array, but it also becomes the most directional, and the sidelobes remain fairly small.

Long compared to the wavelength (1 ) Let s try again, but rather than spacing each antenna of a wavelength apart, let s see about spacing each antenna 1 of a wavelength apart instead. The main lobe is a lot more narrow (not a bad thing!), but some significant sidelobes have formed (not ideal). This can cause a lot of confusion when doing things that require a lot of directional resolution unless they re compensated for.

Going from ( to 5 ) The last model begs the question - what do things look like when you separate the antennas from each other but without moving the beam? Let s simulate moving our antennas but not adjusting the configured beam or operating frequency. Very cool. As the spacing becomes longer in relation to the operating frequency, we can see the sidelobes start to form out of the end of the antenna system.

2x2 Phased Array The second configuration I want to try is a phased array where the elements are in perfect alignment on the z axis, and separated by a fixed offset in either the x or y axis by their neighbor, forming a square when viewed along the x/y axis. Let s take a look at what this looks like for a well constructed 2x2 phased array: Let s do the same as above and take a look at the renders as we play with the configuration of this array and see what things look like. This configuration should suppress the sidelobes and give us good performance, and even give us some amount of control in elevation while we re at it. Sweet. Heck yeah. The array is quite directional in the configured direction, and can even sweep a little bit in elevation, a definite improvement from the 1x4 above.

Long compared to the wavelength (1 ) Let s do the same thing as the 1x4 and take a look at what happens when the distance between elements is long compared to the frequency of operation say, 1 of a wavelength apart? What happens to the sidelobes given this spacing when the frequency of operation is much different than the physical geometry? Mesmerising. This is my favorate render. The sidelobes are very fun to watch come in and out of existence. It looks absolutely other-worldly.

Going from ( to 5 ) Finally, for completeness' sake, what do things look like when you separate the antennas from each other just as we did with the 1x4? Let s simulate moving our antennas but not adjusting the configured beam or operating frequency. Very very cool. The sidelobes wind up turning the very blobby cardioid into an electromagnetic dog toy. I think we ve proven to ourselves that using a phased array much outside its designed frequency of operation seems like a real bad idea.

Future Work Now that I have a system to test things out, I m a bit more confident that my beamforming code is close to right! I d love to push that code over the line and blog about it, since it s a really interesting topic on its own. Once I m sure the code involved isn t full of lies, I ll put it up on the hztools org, and post about it here and on mastodon.