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Donenfeld" , Ard Biesheuvel Cc: Hannes Frederic Sowa , netdev@vger.kernel.org, Linux Kernel Mailing List , Geert Uytterhoeven , Herbert Xu , Jean-Philippe Aumasson , Linux Crypto Mailing List , Erik Kline , Fernando Gont , Lorenzo Colitti , YOSHIFUJI Hideaki Subject: Re: [PATCH RFC v1 2/3] ipv6: move from sha1 to blake2s in address calculation In-Reply-To: References: <20220112131204.800307-1-Jason@zx2c4.com> <20220112131204.800307-3-Jason@zx2c4.com> <87r19cftbr.fsf@toke.dk> <55d185a8-31ea-51d0-d9be-debd490cd204@stressinduktion.org> <87ilung3uo.fsf@toke.dk> X-Clacks-Overhead: GNU Terry Pratchett Date: Thu, 13 Jan 2022 17:18:15 +0100 Message-ID: <878rvjfw3c.fsf@toke.dk> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-crypto@vger.kernel.org "Jason A. Donenfeld" writes: > On Thu, Jan 13, 2022 at 2:50 PM Ard Biesheuvel wrote: >> > Then, at some point down the road, we can talk about removing >> > CONFIG_NET_OBSOLETE_INSECURE_ADDRCONF_HASH too. >> > >> >> What is the point of having CONFIG_OLD_N_CRUSTY if all distros are >> going to enable it indefinitely? > > I think there's probably some combination of > CONFIG_NET_OBSOLETE_INSECURE_ADDRCONF_HASH and CONFIG_OLD_N_CRUSTY and > maybe even a CONFIG_GOD_MURDERS_KITTENS that might be sufficiently > disincentivizing? Or this ties into other general ideas on a gradual > obsolescence->removal flow for things. Making it a compile-time switch doesn't really solve anything, though. It'll need to be a runtime switch for people to be able to opt-in to the new behaviour; otherwise there would still be a flag day when distributions switch on the new config option. I don't think there's any reason to offload this decision on distributions either: there's clearly a "best option" here, absent any backwards compatibility concerns. So it's on us to design a proper transition mechanism. Defaulting to SHA1 when stable_secret is set, as Ard suggested, sounds like a reasonable default; then we only need a single new value for addr_gen_mode to opt-in to using blake2s even when setting the stable_secret. -Toke