Date: Wed, 21 Dec 2016 15:42:33 +0100 From: "Jason A. Donenfeld" <Jason@...c4.com> To: Eric Dumazet <eric.dumazet@...il.com> Cc: George Spelvin <linux@...encehorizons.net>, "Theodore Ts'o" <tytso@....edu>, Andi Kleen <ak@...ux.intel.com>, David Miller <davem@...emloft.net>, David Laight <David.Laight@...lab.com>, "Daniel J . Bernstein" <djb@...yp.to>, Eric Biggers <ebiggers3@...il.com>, Hannes Frederic Sowa <hannes@...essinduktion.org>, Jean-Philippe Aumasson <jeanphilippe.aumasson@...il.com>, kernel-hardening@...ts.openwall.com, Linux Crypto Mailing List <linux-crypto@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, Andy Lutomirski <luto@...capital.net>, Netdev <netdev@...r.kernel.org>, Tom Herbert <tom@...bertland.com>, Linus Torvalds <torvalds@...ux-foundation.org>, Vegard Nossum <vegard.nossum@...il.com> Subject: Re: HalfSipHash Acceptable Usage Hi Eric, I computed performance numbers for both 32-bit and 64-bit using the actual functions in which talking about replacing MD5 with SipHash. The basic harness is here  if you're curious. SipHash was a pretty clear winner for both cases. x86_64: [ 1.714302] secure_tcpv6_sequence_number_md5# cycles: 102373398 [ 1.747685] secure_tcp_sequence_number_md5# cycles: 92042258 [ 1.773522] secure_tcpv6_sequence_number_siphash# cycles: 70786533 [ 1.798701] secure_tcp_sequence_number_siphash# cycles: 68941043 x86: [ 1.635749] secure_tcpv6_sequence_number_md5# cycles: 106016335 [ 1.670259] secure_tcp_sequence_number_md5# cycles: 95670512 [ 1.708387] secure_tcpv6_sequence_number_siphash# cycles: 105988635 [ 1.740264] secure_tcp_sequence_number_siphash# cycles: 88225395 >>> 102373398 > 70786533 True >>> 92042258 > 68941043 True >>> 106016335 > 105988635 True >>> 95670512 > 88225395 True While MD5 is probably faster for some kind of large-data cycles-per-byte, due to its 64-byte internal state, SipHash -- the "Sip" part standing "Short Input PRF" -- is fast for shorter inputs. In practice with the functions we're talking about replacing, there's no need to hash 64-bytes. So, SipHash comes out faster and more secure. I also haven't begun to look focusedly at the assembly my SipHash implemention is generating, which means there's still window for even more performance improvements. Jason  https://git.zx2c4.com/linux-dev/tree/net/core/secure_seq.c?h=siphash-bench#n194
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