Date: Thu, 22 Dec 2016 17:28:43 +0100 From: "Jason A. Donenfeld" <Jason@...c4.com> To: Andy Lutomirski <luto@...capital.net> Cc: Hannes Frederic Sowa <hannes@...essinduktion.org>, Daniel Borkmann <daniel@...earbox.net>, Alexei Starovoitov <alexei.starovoitov@...il.com>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, "Theodore Ts'o" <tytso@....edu>, 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: BPF hash algo (Re: Re: [PATCH v7 3/6] random: use SipHash in place of MD5) Hi all, I don't know what your design requirements are for this. It looks like you're generating some kind of crypto digest of a program, and you need to avoid collisions. If you'd like to go with a PRF (keyed hash function) that uses some kernel secret key, then I'd strongly suggest using Keyed-Blake2. Alternatively, if you need for userspace to be able to calculate the same hash, and don't want to use some kernel secret, then I'd still suggest using Blake2, which will be fast and secure. If you can wait until January, I'll work on a commit adding the primitive to the tree. I've already written it and I just need to get things cleaned up. > Blake2 is both less stable (didn't they slightly change it recently?) No, Blake2 is very stable. It's also extremely secure and has been extensively studied. Not to mention it's faster than SHA2. And if you want to use it as a PRF, it's obvious better suited and faster to use Blake2's keyed PRF mode than HMAC-SHA2. If you don't care about performance, and you don't want to use a PRF, then just use SHA2-256. If you're particularly concerned about certain types of attacks, you could go with SHA2-512 truncated to 256 bytes, but somehow I doubt you need this. Anyway, the take away is: stop using SHA1. It's time has come. > Everyone, please, please, please don't open-code crypto primitives. > Is this and the code above it even correct? It might be but on a very I shuttered looking at this too. How did this possibly make it past review? The attitude toward crypto here is generally *terrifying*. Unless you're a professional cryptographer, the only correct attitude to have is a careful and conservative one. > At the very least, there should be a separate function that calculates > the hash of a buffer and that function should explicitly run itself > against test vectors of various lengths to make sure that it's > calculating what it claims to be calculating. And it doesn't look > like the userspace code has landed, so, if this thing isn't > calculating SHA1 correctly, it's plausible that no one has noticed. If userspace hasn't landed, can we get away with changing this code after 4.10? Or should we just fix it before 4.10? Or should we revert it before 4.10? Development-policy-things like this I have zero clue about, so I heed to your guidance. Jason
Powered by blists - more mailing lists
Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.