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Date: Fri, 14 Jan 2022 18:58:09 +0100 From: "Jason A. Donenfeld" <Jason@...c4.com> To: Hannes Frederic Sowa <hannes@...essinduktion.org> Cc: Toke Høiland-Jørgensen <toke@...hat.com>, Netdev <netdev@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, Geert Uytterhoeven <geert@...ux-m68k.org>, Herbert Xu <herbert@...dor.apana.org.au>, Ard Biesheuvel <ardb@...nel.org>, Jean-Philippe Aumasson <jeanphilippe.aumasson@...il.com>, Linux Crypto Mailing List <linux-crypto@...r.kernel.org>, Erik Kline <ek@...gle.com>, Fernando Gont <fgont@...networks.com>, Lorenzo Colitti <lorenzo@...gle.com>, Hideaki Yoshifuji <hideaki.yoshifuji@...aclelinux.com> Subject: Re: [PATCH RFC v1 2/3] ipv6: move from sha1 to blake2s in address calculation Hi Hannes, On Fri, Jan 14, 2022 at 6:44 PM Hannes Frederic Sowa <hannes@...essinduktion.org> wrote: > I don't think we can argue our way out of this by stating that there are > no guarantees anyway, as much as I would like to change the hash > function as well. Shucks. Alright then. > As much as I know about the problems with SHA1 and would like to see it > removed from the kernel as well, I fear that in this case it seems hard > to do. I would propose putting sha1 into a compilation unit and > overwrite the compiler flags to optimize the function optimized for size > and maybe add another mode or knob to switch the hashing algorithm if > necessary. Already on it! :) https://lore.kernel.org/linux-crypto/20220114154247.99773-3-Jason@zx2c4.com/ > I haven't investigated recent research into breakage of SHA1, I mostly > remember the chosen-image and collision attacks against it. Given the > particular usage of SHA1 in this case, do you think switching the > hashing function increases security? Considering we're only using 64-bits of SHA-1 output, I don't think the SHA-1 collision attacks give you that much here. And it seems like there are other network-level security concerns with the whole scheme anyway. So it might not be the largest of matters. However... > I am asking because of the desire > to decrease the instruction size of the kernel Indeed this is what I was hoping for. Jason
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