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Jason A. Donenfeld authored
commit 1ae2324f upstream. HalfSipHash, or hsiphash, is a shortened version of SipHash, which generates 32-bit outputs using a weaker 64-bit key. It has *much* lower security margins, and shouldn't be used for anything too sensitive, but it could be used as a hashtable key function replacement, if the output is never exposed, and if the security requirement is not too high. The goal is to make this something that performance-critical jhash users would be willing to use. On 64-bit machines, HalfSipHash1-3 is slower than SipHash1-3, so we alias SipHash1-3 to HalfSipHash1-3 on those systems. 64-bit x86_64: [ 0.509409] test_siphash: SipHash2-4 cycles: 4049181 [ 0.510650] test_siphash: SipHash1-3 cycles: 2512884 [ 0.512205] test_siphash: HalfSipHash1-3 cycles: 3429920 [ 0.512904] test_siphash: JenkinsHash cycles: 978267 So, we map hsiphash() -> SipHash1-3 32-bit x86: [ 0.509868] test_siphash: SipHash2-4 cycles: 14812892 [ 0.513601] test_siphash: SipHash1-3 cycles: 9510710 [ 0.515263] test_siphash: HalfSipHash1-3 cycles: 3856157 [ 0.515952] test_siphash: JenkinsHash cycles: 1148567 So, we map hsiphash() -> HalfSipHash1-3 hsiphash() is roughly 3 times slower than jhash(), but comes with a considerable security improvement. Signed-off-by:
Jason A. Donenfeld <Jason@zx2c4.com> Reviewed-by:
Jean-Philippe Aumasson <jeanphilippe.aumasson@gmail.com> Signed-off-by:
David S. Miller <davem@davemloft.net> [bwh: Backported to 3.16 to avoid a build regression for WireGuard with only part of the siphash API available] Signed-off-by:
Ben Hutchings <ben@decadent.org.uk>
Jason A. Donenfeld authoredcommit 1ae2324f upstream. HalfSipHash, or hsiphash, is a shortened version of SipHash, which generates 32-bit outputs using a weaker 64-bit key. It has *much* lower security margins, and shouldn't be used for anything too sensitive, but it could be used as a hashtable key function replacement, if the output is never exposed, and if the security requirement is not too high. The goal is to make this something that performance-critical jhash users would be willing to use. On 64-bit machines, HalfSipHash1-3 is slower than SipHash1-3, so we alias SipHash1-3 to HalfSipHash1-3 on those systems. 64-bit x86_64: [ 0.509409] test_siphash: SipHash2-4 cycles: 4049181 [ 0.510650] test_siphash: SipHash1-3 cycles: 2512884 [ 0.512205] test_siphash: HalfSipHash1-3 cycles: 3429920 [ 0.512904] test_siphash: JenkinsHash cycles: 978267 So, we map hsiphash() -> SipHash1-3 32-bit x86: [ 0.509868] test_siphash: SipHash2-4 cycles: 14812892 [ 0.513601] test_siphash: SipHash1-3 cycles: 9510710 [ 0.515263] test_siphash: HalfSipHash1-3 cycles: 3856157 [ 0.515952] test_siphash: JenkinsHash cycles: 1148567 So, we map hsiphash() -> HalfSipHash1-3 hsiphash() is roughly 3 times slower than jhash(), but comes with a considerable security improvement. Signed-off-by:
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siphash.c 11.70 KiB
/* Copyright (C) 2016 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
*
* This file is provided under a dual BSD/GPLv2 license.
*
* SipHash: a fast short-input PRF
* https://131002.net/siphash/
*
* This implementation is specifically for SipHash2-4 for a secure PRF
* and HalfSipHash1-3/SipHash1-3 for an insecure PRF only suitable for
* hashtables.
*/
#include <linux/siphash.h>
#include <asm/unaligned.h>
#if defined(CONFIG_DCACHE_WORD_ACCESS) && BITS_PER_LONG == 64
#include <linux/dcache.h>
#include <asm/word-at-a-time.h>
#endif
#define SIPROUND \
do { \
v0 += v1; v1 = rol64(v1, 13); v1 ^= v0; v0 = rol64(v0, 32); \
v2 += v3; v3 = rol64(v3, 16); v3 ^= v2; \
v0 += v3; v3 = rol64(v3, 21); v3 ^= v0; \
v2 += v1; v1 = rol64(v1, 17); v1 ^= v2; v2 = rol64(v2, 32); \
} while (0)
#define PREAMBLE(len) \
u64 v0 = 0x736f6d6570736575ULL; \
u64 v1 = 0x646f72616e646f6dULL; \
u64 v2 = 0x6c7967656e657261ULL; \
u64 v3 = 0x7465646279746573ULL; \
u64 b = ((u64)(len)) << 56; \
v3 ^= key->key[1]; \
v2 ^= key->key[0]; \
v1 ^= key->key[1]; \
v0 ^= key->key[0];
#define POSTAMBLE \
v3 ^= b; \
SIPROUND; \
SIPROUND; \
v0 ^= b; \
v2 ^= 0xff; \
SIPROUND; \
SIPROUND; \
SIPROUND; \
SIPROUND; \
return (v0 ^ v1) ^ (v2 ^ v3);
u64 __siphash_aligned(const void *data, size_t len, const siphash_key_t *key)
{
const u8 *end = data + len - (len % sizeof(u64));
const u8 left = len & (sizeof(u64) - 1);
u64 m;
PREAMBLE(len)
for (; data != end; data += sizeof(u64)) {
m = le64_to_cpup(data);
v3 ^= m;
SIPROUND;
SIPROUND;
v0 ^= m;
}
#if defined(CONFIG_DCACHE_WORD_ACCESS) && BITS_PER_LONG == 64
if (left)
b |= le64_to_cpu((__force __le64)(load_unaligned_zeropad(data) &
bytemask_from_count(left)));
#else
switch (left) {