Date: Mon, 28 Dec 2020 17:19:39 -0800 From: John-Mark Gurney <jmg@funkthat.com> To: Brooks Davis <brooks@freebsd.org>, Thomas Mueller <mueller6722@twc.com>, freebsd-current@freebsd.org Subject: Re: HEADS UP: FreeBSD src repo transitioning to git this weekend Message-ID: <20201229011939.GU31099@funkthat.com> In-Reply-To: <20201223162417.v7Ce6%steffen@sdaoden.eu> References: <CANCZdfrUsaw5jpN1ybpk0ADXdQYam0_NO0mPJd0-FMbuxPruhw@mail.gmail.com> <31ab8015-a0c4-af77-0ead-a17da0f88f1d@freebsd.org> <CANCZdfrF0B7uux_neg-4XGn2UCDd4noUm7zP_icHnrpZUgmzzA@mail.gmail.com> <CAOtMX2gV2dmyG4b1hZG24sUnqDVk=1pch4xgQmyUdtLrh48kYg@mail.gmail.com> <CANCZdfpb0MF%2BuoW=K3cQpL%2B3vNQjSBDeVMab5d4JJhUO4sy-2Q@mail.gmail.com> <5fdc0b90.1c69fb81.866eb.8c29SMTPIN_ADDED_MISSING@mx.google.com> <20201218175241.GA72552@spindle.one-eyed-alien.net> <20201218182820.1P0tK%steffen@sdaoden.eu> <20201223023242.GG31099@funkthat.com> <20201223162417.v7Ce6%steffen@sdaoden.eu>
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Steffen Nurpmeso wrote this message on Wed, Dec 23, 2020 at 17:24 +0100: > |Then there's also the point that the repo is (looks like it) using > |SHA-1 hashes, which are effectively broken, so depending upon them > |to validate the tree is questionable anyways. > > git uses the hardened SHA-1 for sure, which is, as far as i know, > at least safe against the known attack. > I .. have not tracked this, but i think upgrading to SHA-256 is > possible, once this will become standard. Just even more > metadata, then. I have not looked into this, still in progress. A new attack came out earlier this year: https://eprint.iacr.org/2020/014.pdf >From the paper: > In particular, chosen-prefix collisions can break signature schemes and > handshake security in secure channel protocols (TLS, SSH), if generated > extremely quickly. The previous attack in 2017 did not break SHA-1 enough to render it's use by git vulnerable, but the writing was on the wall for SHA-1... I believe this new attack makes git's use a SHA-1 vulnerable... The type/length prefix that prevented the previous attacks from working is not effective against the new attack... Also, the cost of the attack is not great ($45k), considering the recent SolarWinds supply chain attack, being able to smuggle a modified file into a git repo, say an OS's build server, such that the tools don't know the tree is modified is a real problem... -- John-Mark Gurney Voice: +1 415 225 5579 "All that I will do, has been done, All that I have, has not."
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