# Re: Migrating away from SHA-1? 3 messages from 2016-06-18 to 2016-06-24. Participants: Leo Gaspard, Eric Wong, brian m. carlson. Thread: https://gitlist.dev/t/42646 ## Leo Gaspard, 2016-06-18 02:10 Subject: Re: Migrating away from SHA-1? Message-ID: <02b42587-3643-1c2e-c249-313ec96bcdca@gaspard.io> URL: https://gitlist.dev/e/02b42587-3643-1c2e-c249-313ec96bcdca%40gaspard.io ``` First, sorry for not having this message threaded: I'm not subscribed to the list and haven't found a way to get a Message-Id from gmane. I just wanted to ask, as an end-user highly relying on commit signatures, a few questions as to the migration away from SHA-1. SHA-1 already suffers from a freestart collision attack. Based on what I understand of the object model of git, a chosen-prefix collision attack (perhaps somewhat improved) is enough to make reviewers accept a patch, sign it, and then swap the innocuous-looking patch for an evil-doing one -- which *will be signed*. As for the issue about code checking being an easier entrypoint (Theodore Ts'o, 2016-04-14 22:40:51 GMT), in a use case of mine there is a repo with my dotfiles on an untrusted server. Yet I download them and am able to execute them without fear because each commit is PGP-signed with my key. The point being that code checking is not even a possible entrypoint in some cases, so SHA-1 seems to be(come) the weakest link. So, I don't think it is possible to disagree with Jeff King when he wrote his 2016-04-12 23:15:19 GMT email. Peter Anvin (2016-04-14 17:28:50 GMT) gets a point in that there is no need to hurry (chosen-prefix collisions may be still quite a long way, even though there is no guesswork in these matters), and quality is important. Yet Jeff King's proposal (2016-04-12 23:42:52 GMT), amended by Junio Hamano (2016-04-13 01:03:02 GMT) and himself (2016-04-13 01:36:32 GMT) seem to have met no opposition. So, my questions to the git team: * Is there a consensus, that git should migrate away from SHA-1 before it gets a collision attack, because it would mean chosen-prefix collision isn't far away and people wouldn't have the time to upgrade? * Is there a consensus, that Peter Anvin's amended transition plan is the way to go? * If the two conditions above are fulfilled, has work started on it yet? (I guess as Brian Carlson had started his work 9 weeks ago and he was speaking about working on it on the week-end he should have finished it now, so excluding this) * If the two first conditions are fulfilled, is there anything I could do to help this transition? (including helping Brian if his work hasn't actually ended yet) Sorry for bringing up again a subject that seems to be quite recurrent, and for this long block of text, Leo Gaspard ``` ## Eric Wong, 2016-06-18 03:30 Subject: Re: Migrating away from SHA-1? Message-ID: <20160618033019.GB11307@dcvr.yhbt.net> URL: https://gitlist.dev/e/20160618033019.GB11307%40dcvr.yhbt.net In-Reply-To: <02b42587-3643-1c2e-c249-313ec96bcdca@gaspard.io> ``` Leo Gaspard wrote: > First, sorry for not having this message threaded: I'm not subscribed to > the list and haven't found a way to get a Message-Id from gmane. Appending "/raw" to the gmane URL will get you the raw message with full headers: article.gmane.org/gmane.comp.version-control.git/$NUMBER/raw you can also use that article $NUMBER via NNTP on news.gmane.org > So, my questions to the git team: It is customary to Cc: all relevant parties involved with that thread since they may not all be subscribed, either. > * Is there a consensus, that git should migrate away from SHA-1 before > it gets a collision attack, because it would mean chosen-prefix > collision isn't far away and people wouldn't have the time to upgrade? > * Is there a consensus, that Peter Anvin's amended transition plan is > the way to go? > * If the two conditions above are fulfilled, has work started on it > yet? (I guess as Brian Carlson had started his work 9 weeks ago and he > was speaking about working on it on the week-end he should have finished > it now, so excluding this) AFAIK, brian is still working on it. Last series on the matter begins here: http://mid.gmane.org/20160607005716.69222-2-sandals@crustytoothpaste.net I'm just on the sidelines observing :) > * If the two first conditions are fulfilled, is there anything I could > do to help this transition? (including helping Brian if his work hasn't > actually ended yet) ``` ## brian m. carlson, 2016-06-24 18:17 Subject: Re: Migrating away from SHA-1? Message-ID: <20160624181705.GA7035@vauxhall.crustytoothpaste.net> URL: https://gitlist.dev/e/20160624181705.GA7035%40vauxhall.crustytoothpaste.net In-Reply-To: <02b42587-3643-1c2e-c249-313ec96bcdca@gaspard.io> ``` On Sat, Jun 18, 2016 at 03:10:27AM +0100, Leo Gaspard wrote: > First, sorry for not having this message threaded: I'm not subscribed to > the list and haven't found a way to get a Message-Id from gmane. Sorry it's taken so long to get back to this. I've been at a conference. > So, my questions to the git team: > * Is there a consensus, that git should migrate away from SHA-1 before > it gets a collision attack, because it would mean chosen-prefix > collision isn't far away and people wouldn't have the time to upgrade? I plan on adding support for a new hash as soon as that's possible, but I don't have a firm timeline. This is a volunteer effort in my own limited free time. > * Is there a consensus, that Peter Anvin's amended transition plan is > the way to go? I'm not planning on changing algorithms in the middle of a repository. This will only be available on new or imported repositories. My current thinking on proposed algorithms is SHA3-256 or BLAKE2b-256. The cryptanalysis on SHA-256 indicates that it may not be a great long-term choice, and I expect people won't want to change algorithms frequently. If time becomes extremely urgent, we can always add support for a 160-bit hash first (e.g. BLAKE2b-160) and then finish the object_id transition later as it becomes convenient. I'd like to avoid that, though. > * If the two conditions above are fulfilled, has work started on it > yet? (I guess as Brian Carlson had started his work 9 weeks ago and he > was speaking about working on it on the week-end he should have finished > it now, so excluding this) It takes a long time to get a patch series through. I'm rather busy and don't always have time to rebase and address issues during the week. > * If the two first conditions are fulfilled, is there anything I could > do to help this transition? (including helping Brian if his work hasn't > actually ended yet) You're welcome to send patches if you like. I try to avoid areas I know are under heavy development, like the refs code. -- brian m. carlson / brian with sandals: Houston, Texas, US +1 832 623 2791 | https://www.crustytoothpaste.net/~bmc | My opinion only OpenPGP: https://keybase.io/bk2204 ```