Date: Thu, 22 Dec 2016 16:51:40 +0100 From: Hannes Frederic Sowa <hannes@...essinduktion.org> To: "Jason A. Donenfeld" <Jason@...c4.com> Cc: kernel-hardening@...ts.openwall.com, Theodore Ts'o <tytso@....edu>, Andy Lutomirski <luto@...capital.net>, Netdev <netdev@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, Linux Crypto Mailing List <linux-crypto@...r.kernel.org>, David Laight <David.Laight@...lab.com>, Eric Dumazet <edumazet@...gle.com>, Linus Torvalds <torvalds@...ux-foundation.org>, Eric Biggers <ebiggers3@...il.com>, Tom Herbert <tom@...bertland.com>, Andi Kleen <ak@...ux.intel.com>, "David S. Miller" <davem@...emloft.net>, Jean-Philippe Aumasson <jeanphilippe.aumasson@...il.com> Subject: Re: Re: [PATCH v7 3/6] random: use SipHash in place of MD5 On Thu, 2016-12-22 at 16:41 +0100, Jason A. Donenfeld wrote: > Hi Hannes, > > On Thu, Dec 22, 2016 at 4:33 PM, Hannes Frederic Sowa > <hannes@...essinduktion.org> wrote: > > IPv6 you cannot touch anymore. The hashing algorithm is part of uAPI. > > You don't want to give people new IPv6 addresses with the same stable > > secret (across reboots) after a kernel upgrade. Maybe they lose > > connectivity then and it is extra work? > > Ahh, too bad. So it goes. If no other users survive we can put it into the ipv6 module. > > The bpf hash stuff can be changed during this merge window, as it is > > not yet in a released kernel. Albeit I would probably have preferred > > something like sha256 here, which can be easily replicated by user > > space tools (minus the problem of patching out references to not > > hashable data, which must be zeroed). > > Oh, interesting, so time is of the essence then. Do you want to handle > changing the new eBPF code to something not-SHA1 before it's too late, > as part of a new patchset that can fast track itself to David? And > then I can preserve my large series for the next merge window. This algorithm should be a non-seeded algorithm, because the hashes should be stable and verifiable by user space tooling. Thus this would need a hashing algorithm that is hardened against pre-image attacks/collision resistance, which siphash is not. I would prefer some higher order SHA algorithm for that actually. Bye, Hannes
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