Okay, since there’s so much stuff to digest here and apparently there are issues designated as wontfix by GnuPG maintainers, can someone more in the loop tell us whether using gpg signatures on git commits/tags is vulnerable? And is there any better alternative going forward? Like is signing with SSH keys considered more secure now? I certainly want to get rid of gpg from my life if I can, but I also need to make sure commits/tags bearing my name actually come from me.
One of those WONTFIX's is on an insane vulnerability: you can bitflip known plaintext in a PGP message to switch it into handling compression, allowing attackers to instruct GnuPG packet processing to look back to arbitrary positions in the message, all while suppressing the authentication failure message. GPG's position was: they print, in those circumstances, an error of some sort, and that's enough. It's an attack that reveals plaintext bytes!
These are not vulnerabilities in the "remote exploit" sense. They should be taken seriously, you should be careful not to run local software on untrusted data, and GPG should probably do more to protect users from shooting themselves in the foot, but the worst thing you could do is panic and throw out a process your partners and colleagues trust. There is nothing here that will disturb your workflow signing commits or apt-get install-ing from your distribution.
If you use crypographic command line tools to verify data sent to you, be mindful on what you are doing and make sure to understand the attacks presented here. One of the slides is titled "should we even use command line tools" and yes, we should because the alternative is worse, but we must be diligent in treating all untrusted data as adversarial.
A huge part of GPG’s purported use case is getting a signed/encrypted/both blob from somebody and using GPG to confirm it’s authentic. This is true for packages you download and for commits with signatures.
It is, and other software handling untrusted data should also treat it as adversarial. For example, your package tool should probably not output raw package metadata to the terminal.
I did the switch this year after getting yet another personal computer. I have 4 in total (work laptop, personal sofa laptop, Mac Mini, Linux Tower). I used Yubi keys with gpg and resident ssh keys. All is fine but the configuration needed to get it too work on all the machines. I also tend to forget the finer details and have to relearn the skills of fetching the public keys into the keychain etc. I got rid of this all by moving to 1Password ssh agent and git ssh signing. Removes a lot of headaches from my ssh setup. I still have the yubi key(s) though as a 2nd factor for certain web services. And the gpg agent is still running but only as a fallback. I will turn this off next year.
Maybe the site is overloaded. But as for the "brb, were on it!!!!" - this page had the live stream of the talk when it was happening. Hopefully they'll replace it with the recording when media.ccc.de posts it, which should be within a couple hours.
This feels pretty unsatisfying: something that’s been “considered harmful” for three decades should be deprecated and then removed in a responsible ecosystem.
(PGP/GPG are of course hamstrung by their own decision to be a Swiss Army knife/only loosely coupled to the secure operation itself. So the even more responsible thing to do is to discard them for purposes that they can’t offer security properties for, which is the vast majority of things they get used for.)
Can you provide a source this? To my understanding, the GnuPG project (and by extension PGP as an ecosystem) considers itself very much alive, even though practically speaking it’s effectively moribund and irrelevant.
(So I agree that it’s de facto dead, but that’s not the same thing as formal deprecation. The latter is what you do explicitly to responsibly move people away from something that’s not suitable for use anymore.)
From what I can piece together while the site is down, it seems like they've uncovered 14 exploitable vulnerabilities in GnuPG, of which most remain unpatched. Some of those are apparently met by refusal to patch by the maintainer. Maybe there are good reasons for this refusal, maybe someone else can chime in on that?
Is this another case of XKCD-2347? Or is there something else going on? Pretty much every Linux distro depends on PGP being pretty secure. Surely IBM & co have a couple of spare developers or spare cash to contribute?
> Surely IBM & co have a couple of spare developers or spare cash to contribute?
A major part of the problem is that GPG’s issues aren’t cash or developer time. It’s fundamentally a bad design for cryptographic usage. It’s so busy trying to be a generic Swiss Army knife for every possible user or use case that it’s basically made of developer and user footguns.
The way you secure this is by moving to alternative, purpose-built tools. Signal/WhatsApp for messaging, age for file encryption, minisign for signatures, etc.
It was a cleartext signature, not a detached signature.
Edit: even better. It was both. There is a signature type confusion attack going on here. I still didn't watch the entire thing, but it seems that unlike gpg, they do have to specify --cleartext explicitly for Sequoia, so there is no confusion going on that case.
A thru-line of some of the gnarliest vulnerabilities here is PGP's insane packet system, where a PGP message is a practically arbitrary stream of packets, some control and some data, with totally incoherent cryptographic bindings. It's like something in between XMLDSIG (which pulls cryptographic control data out of random places in XML messages according to attacker-controlled tags) and SSL2 (with no coherent authentication of the complete handshake).
The attack on detached signatures (attack #1) happens because GnuPG needs to run a complicated state machine that can put processing into multiple different modes, among them three different styles of message signature. In GPG, that whole state machine apparently collapses down to a binary check of "did we see any data so that we'd need to verify a signature?", and you can selectively flip that predicate back and forth by shoving different packets into message stream, even if you've already sent data that needs to be verified.
The malleability bug (attack #4) is particularly slick. Again, it's an incoherent state machine issue. GPG can "fail" to process a packet because it's cryptographically invalid. But it can also fail because the message framing itself is corrupted. Those latter non-cryptographic failures are handled by aborting the processing of the message, putting GPG into an unexpected state where it's handling an error and "forgetting" to check the message authenticator. You can CBC-bitflip known headers to force GPG into processing DEFLATE compression, and mangle the message such that handling the message prints the plaintext in its output.
The formfeed bug (#3) is downright weird. GnuPG has special handling for `\f`; if it occurs at the end of a line, you can inject arbitrary unsigned data, because of GnuPG's handling of line truncation. Why is this even a feature?
Some of these attacks look situational, but that's deceptive, because PGP is (especially in older jankier systems) used as an encryption backend for applications --- Mallory getting Alice to sign or encrypt something on her behalf is an extremely realistic threat model (it's the same threat model as most cryptographic attacks on secure cookies: the app automatically signs stuff for users).
There is no reason for a message encryption system to have this kind of complexity. It's a deep architectural flaw in PGP. You want extremely simple, orthogonal features in the format, ideally treating everything as clearly length-delimited opaque binary blobs. Instead you get a Weird Machine, and talks like this one.
AFAICT this is GnuPG specific and not OpenPGP related? Since GnuPG has pulled out of standards compliance anyway there are many better options. Sequoia chameleon even has drop in tooling for most workflows.
They presented critical parser flaws in all major PGP implementations, not just GNU PGP, also sequoia, minisign and age. But gpg made the worst impression to us. wontfix
Nope. Not yet enabled. It was submitted to HN right after the talk where they promised to make it public "really soon" after the talk. We all saw the talk live or on the stream
If you use crypographic command line tools to verify data sent to you, be mindful on what you are doing and make sure to understand the attacks presented here. One of the slides is titled "should we even use command line tools" and yes, we should because the alternative is worse, but we must be diligent in treating all untrusted data as adversarial.
Handling untrusted input is core to that.
I’m still working through how to use this but I have it basically setup and it’s great!
As they said, they were on it...
Archive link: https://web.archive.org/web/20251227174414/https://www.gnupg...
(PGP/GPG are of course hamstrung by their own decision to be a Swiss Army knife/only loosely coupled to the secure operation itself. So the even more responsible thing to do is to discard them for purposes that they can’t offer security properties for, which is the vast majority of things they get used for.)
(I think you already know this, but want to relitigate something that’s not meaningfully controversial in Python.)
Most people have never heard of it and never used it.
(So I agree that it’s de facto dead, but that’s not the same thing as formal deprecation. The latter is what you do explicitly to responsibly move people away from something that’s not suitable for use anymore.)
it's the GnuPG blog on gnupg.org with multiple authors.
this is a post by Werner Koch, not his blog.
But trust in Werner Koch is gone. Wontfix??
People who are serious about security use newer, better tools that replace GPG. But keep in mind, there’s no “one ring to rule them all”.
From what I can piece together while the site is down, it seems like they've uncovered 14 exploitable vulnerabilities in GnuPG, of which most remain unpatched. Some of those are apparently met by refusal to patch by the maintainer. Maybe there are good reasons for this refusal, maybe someone else can chime in on that?
Is this another case of XKCD-2347? Or is there something else going on? Pretty much every Linux distro depends on PGP being pretty secure. Surely IBM & co have a couple of spare developers or spare cash to contribute?
A major part of the problem is that GPG’s issues aren’t cash or developer time. It’s fundamentally a bad design for cryptographic usage. It’s so busy trying to be a generic Swiss Army knife for every possible user or use case that it’s basically made of developer and user footguns.
The way you secure this is by moving to alternative, purpose-built tools. Signal/WhatsApp for messaging, age for file encryption, minisign for signatures, etc.
I haven't seen those outside of old mailing list archives. Everyone uses detached signatures nowadays, e.g. PGP/MIME for emails.
Edit: even better. It was both. There is a signature type confusion attack going on here. I still didn't watch the entire thing, but it seems that unlike gpg, they do have to specify --cleartext explicitly for Sequoia, so there is no confusion going on that case.
The attack on detached signatures (attack #1) happens because GnuPG needs to run a complicated state machine that can put processing into multiple different modes, among them three different styles of message signature. In GPG, that whole state machine apparently collapses down to a binary check of "did we see any data so that we'd need to verify a signature?", and you can selectively flip that predicate back and forth by shoving different packets into message stream, even if you've already sent data that needs to be verified.
The malleability bug (attack #4) is particularly slick. Again, it's an incoherent state machine issue. GPG can "fail" to process a packet because it's cryptographically invalid. But it can also fail because the message framing itself is corrupted. Those latter non-cryptographic failures are handled by aborting the processing of the message, putting GPG into an unexpected state where it's handling an error and "forgetting" to check the message authenticator. You can CBC-bitflip known headers to force GPG into processing DEFLATE compression, and mangle the message such that handling the message prints the plaintext in its output.
The formfeed bug (#3) is downright weird. GnuPG has special handling for `\f`; if it occurs at the end of a line, you can inject arbitrary unsigned data, because of GnuPG's handling of line truncation. Why is this even a feature?
Some of these attacks look situational, but that's deceptive, because PGP is (especially in older jankier systems) used as an encryption backend for applications --- Mallory getting Alice to sign or encrypt something on her behalf is an extremely realistic threat model (it's the same threat model as most cryptographic attacks on secure cookies: the app automatically signs stuff for users).
There is no reason for a message encryption system to have this kind of complexity. It's a deep architectural flaw in PGP. You want extremely simple, orthogonal features in the format, ideally treating everything as clearly length-delimited opaque binary blobs. Instead you get a Weird Machine, and talks like this one.
Amazing work.