Commit 1ae2324f authored by Jason A. Donenfeld's avatar Jason A. Donenfeld Committed by David S. Miller

siphash: implement HalfSipHash1-3 for hash tables

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: 's avatarJason A. Donenfeld <Jason@zx2c4.com>
Reviewed-by: 's avatarJean-Philippe Aumasson <jeanphilippe.aumasson@gmail.com>
Signed-off-by: 's avatarDavid S. Miller <davem@davemloft.net>
parent 2c956a60
......@@ -98,3 +98,78 @@ u64 h = siphash(&combined, offsetofend(typeof(combined), dport), &secret);
Read the SipHash paper if you're interested in learning more:
https://131002.net/siphash/siphash.pdf
~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~=~
HalfSipHash - SipHash's insecure younger cousin
-----------------------------------------------
Written by Jason A. Donenfeld <jason@zx2c4.com>
On the off-chance that SipHash is not fast enough for your needs, you might be
able to justify using HalfSipHash, a terrifying but potentially useful
possibility. HalfSipHash cuts SipHash's rounds down from "2-4" to "1-3" and,
even scarier, uses an easily brute-forcable 64-bit key (with a 32-bit output)
instead of SipHash's 128-bit key. However, this may appeal to some
high-performance `jhash` users.
Danger!
Do not ever use HalfSipHash except for as a hashtable key function, and only
then when you can be absolutely certain that the outputs will never be
transmitted out of the kernel. This is only remotely useful over `jhash` as a
means of mitigating hashtable flooding denial of service attacks.
1. Generating a key
Keys should always be generated from a cryptographically secure source of
random numbers, either using get_random_bytes or get_random_once:
hsiphash_key_t key;
get_random_bytes(&key, sizeof(key));
If you're not deriving your key from here, you're doing it wrong.
2. Using the functions
There are two variants of the function, one that takes a list of integers, and
one that takes a buffer:
u32 hsiphash(const void *data, size_t len, const hsiphash_key_t *key);
And:
u32 hsiphash_1u32(u32, const hsiphash_key_t *key);
u32 hsiphash_2u32(u32, u32, const hsiphash_key_t *key);
u32 hsiphash_3u32(u32, u32, u32, const hsiphash_key_t *key);
u32 hsiphash_4u32(u32, u32, u32, u32, const hsiphash_key_t *key);
If you pass the generic hsiphash function something of a constant length, it
will constant fold at compile-time and automatically choose one of the
optimized functions.
3. Hashtable key function usage:
struct some_hashtable {
DECLARE_HASHTABLE(hashtable, 8);
hsiphash_key_t key;
};
void init_hashtable(struct some_hashtable *table)
{
get_random_bytes(&table->key, sizeof(table->key));
}
static inline hlist_head *some_hashtable_bucket(struct some_hashtable *table, struct interesting_input *input)
{
return &table->hashtable[hsiphash(input, sizeof(*input), &table->key) & (HASH_SIZE(table->hashtable) - 1)];
}
You may then iterate like usual over the returned hash bucket.
4. Performance
HalfSipHash is roughly 3 times slower than JenkinsHash. For many replacements,
this will not be a problem, as the hashtable lookup isn't the bottleneck. And
in general, this is probably a good sacrifice to make for the security and DoS
resistance of HalfSipHash.
......@@ -5,7 +5,9 @@
* SipHash: a fast short-input PRF
* https://131002.net/siphash/
*
* This implementation is specifically for SipHash2-4.
* This implementation is specifically for SipHash2-4 for a secure PRF
* and HalfSipHash1-3/SipHash1-3 for an insecure PRF only suitable for
* hashtables.
*/
#ifndef _LINUX_SIPHASH_H
......@@ -82,4 +84,57 @@ static inline u64 siphash(const void *data, size_t len,
return ___siphash_aligned(data, len, key);
}
#define HSIPHASH_ALIGNMENT __alignof__(unsigned long)
typedef struct {
unsigned long key[2];
} hsiphash_key_t;
u32 __hsiphash_aligned(const void *data, size_t len,
const hsiphash_key_t *key);
#ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
u32 __hsiphash_unaligned(const void *data, size_t len,
const hsiphash_key_t *key);
#endif
u32 hsiphash_1u32(const u32 a, const hsiphash_key_t *key);
u32 hsiphash_2u32(const u32 a, const u32 b, const hsiphash_key_t *key);
u32 hsiphash_3u32(const u32 a, const u32 b, const u32 c,
const hsiphash_key_t *key);
u32 hsiphash_4u32(const u32 a, const u32 b, const u32 c, const u32 d,
const hsiphash_key_t *key);
static inline u32 ___hsiphash_aligned(const __le32 *data, size_t len,
const hsiphash_key_t *key)
{
if (__builtin_constant_p(len) && len == 4)
return hsiphash_1u32(le32_to_cpu(data[0]), key);
if (__builtin_constant_p(len) && len == 8)
return hsiphash_2u32(le32_to_cpu(data[0]), le32_to_cpu(data[1]),
key);
if (__builtin_constant_p(len) && len == 12)
return hsiphash_3u32(le32_to_cpu(data[0]), le32_to_cpu(data[1]),
le32_to_cpu(data[2]), key);
if (__builtin_constant_p(len) && len == 16)
return hsiphash_4u32(le32_to_cpu(data[0]), le32_to_cpu(data[1]),
le32_to_cpu(data[2]), le32_to_cpu(data[3]),
key);
return __hsiphash_aligned(data, len, key);
}
/**
* hsiphash - compute 32-bit hsiphash PRF value
* @data: buffer to hash
* @size: size of @data
* @key: the hsiphash key
*/
static inline u32 hsiphash(const void *data, size_t len,
const hsiphash_key_t *key)
{
#ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
if (!IS_ALIGNED((unsigned long)data, HSIPHASH_ALIGNMENT))
return __hsiphash_unaligned(data, len, key);
#endif
return ___hsiphash_aligned(data, len, key);
}
#endif /* _LINUX_SIPHASH_H */
......@@ -5,7 +5,9 @@
* SipHash: a fast short-input PRF
* https://131002.net/siphash/
*
* This implementation is specifically for SipHash2-4.
* 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>
......@@ -230,3 +232,320 @@ u64 siphash_3u32(const u32 first, const u32 second, const u32 third,
POSTAMBLE
}
EXPORT_SYMBOL(siphash_3u32);
#if BITS_PER_LONG == 64
/* Note that on 64-bit, we make HalfSipHash1-3 actually be SipHash1-3, for
* performance reasons. On 32-bit, below, we actually implement HalfSipHash1-3.
*/
#define HSIPROUND SIPROUND
#define HPREAMBLE(len) PREAMBLE(len)
#define HPOSTAMBLE \
v3 ^= b; \
HSIPROUND; \
v0 ^= b; \
v2 ^= 0xff; \
HSIPROUND; \
HSIPROUND; \
HSIPROUND; \
return (v0 ^ v1) ^ (v2 ^ v3);
u32 __hsiphash_aligned(const void *data, size_t len, const hsiphash_key_t *key)
{
const u8 *end = data + len - (len % sizeof(u64));
const u8 left = len & (sizeof(u64) - 1);
u64 m;
HPREAMBLE(len)
for (; data != end; data += sizeof(u64)) {
m = le64_to_cpup(data);
v3 ^= m;
HSIPROUND;
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) {
case 7: b |= ((u64)end[6]) << 48;
case 6: b |= ((u64)end[5]) << 40;
case 5: b |= ((u64)end[4]) << 32;
case 4: b |= le32_to_cpup(data); break;
case 3: b |= ((u64)end[2]) << 16;
case 2: b |= le16_to_cpup(data); break;
case 1: b |= end[0];
}
#endif
HPOSTAMBLE
}
EXPORT_SYMBOL(__hsiphash_aligned);
#ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
u32 __hsiphash_unaligned(const void *data, size_t len,
const hsiphash_key_t *key)
{
const u8 *end = data + len - (len % sizeof(u64));
const u8 left = len & (sizeof(u64) - 1);
u64 m;
HPREAMBLE(len)
for (; data != end; data += sizeof(u64)) {
m = get_unaligned_le64(data);
v3 ^= m;
HSIPROUND;
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) {
case 7: b |= ((u64)end[6]) << 48;
case 6: b |= ((u64)end[5]) << 40;
case 5: b |= ((u64)end[4]) << 32;
case 4: b |= get_unaligned_le32(end); break;
case 3: b |= ((u64)end[2]) << 16;
case 2: b |= get_unaligned_le16(end); break;
case 1: b |= end[0];
}
#endif
HPOSTAMBLE
}
EXPORT_SYMBOL(__hsiphash_unaligned);
#endif
/**
* hsiphash_1u32 - compute 64-bit hsiphash PRF value of a u32
* @first: first u32
* @key: the hsiphash key
*/
u32 hsiphash_1u32(const u32 first, const hsiphash_key_t *key)
{
HPREAMBLE(4)
b |= first;
HPOSTAMBLE
}
EXPORT_SYMBOL(hsiphash_1u32);
/**
* hsiphash_2u32 - compute 32-bit hsiphash PRF value of 2 u32
* @first: first u32
* @second: second u32
* @key: the hsiphash key
*/
u32 hsiphash_2u32(const u32 first, const u32 second, const hsiphash_key_t *key)
{
u64 combined = (u64)second << 32 | first;
HPREAMBLE(8)
v3 ^= combined;
HSIPROUND;
v0 ^= combined;
HPOSTAMBLE
}
EXPORT_SYMBOL(hsiphash_2u32);
/**
* hsiphash_3u32 - compute 32-bit hsiphash PRF value of 3 u32
* @first: first u32
* @second: second u32
* @third: third u32
* @key: the hsiphash key
*/
u32 hsiphash_3u32(const u32 first, const u32 second, const u32 third,
const hsiphash_key_t *key)
{
u64 combined = (u64)second << 32 | first;
HPREAMBLE(12)
v3 ^= combined;
HSIPROUND;
v0 ^= combined;
b |= third;
HPOSTAMBLE
}
EXPORT_SYMBOL(hsiphash_3u32);
/**
* hsiphash_4u32 - compute 32-bit hsiphash PRF value of 4 u32
* @first: first u32
* @second: second u32
* @third: third u32
* @forth: forth u32
* @key: the hsiphash key
*/
u32 hsiphash_4u32(const u32 first, const u32 second, const u32 third,
const u32 forth, const hsiphash_key_t *key)
{
u64 combined = (u64)second << 32 | first;
HPREAMBLE(16)
v3 ^= combined;
HSIPROUND;
v0 ^= combined;
combined = (u64)forth << 32 | third;
v3 ^= combined;
HSIPROUND;
v0 ^= combined;
HPOSTAMBLE
}
EXPORT_SYMBOL(hsiphash_4u32);
#else
#define HSIPROUND \
do { \
v0 += v1; v1 = rol32(v1, 5); v1 ^= v0; v0 = rol32(v0, 16); \
v2 += v3; v3 = rol32(v3, 8); v3 ^= v2; \
v0 += v3; v3 = rol32(v3, 7); v3 ^= v0; \
v2 += v1; v1 = rol32(v1, 13); v1 ^= v2; v2 = rol32(v2, 16); \
} while (0)
#define HPREAMBLE(len) \
u32 v0 = 0; \
u32 v1 = 0; \
u32 v2 = 0x6c796765U; \
u32 v3 = 0x74656462U; \
u32 b = ((u32)(len)) << 24; \
v3 ^= key->key[1]; \
v2 ^= key->key[0]; \
v1 ^= key->key[1]; \
v0 ^= key->key[0];
#define HPOSTAMBLE \
v3 ^= b; \
HSIPROUND; \
v0 ^= b; \
v2 ^= 0xff; \
HSIPROUND; \
HSIPROUND; \
HSIPROUND; \
return v1 ^ v3;
u32 __hsiphash_aligned(const void *data, size_t len, const hsiphash_key_t *key)
{
const u8 *end = data + len - (len % sizeof(u32));
const u8 left = len & (sizeof(u32) - 1);
u32 m;
HPREAMBLE(len)
for (; data != end; data += sizeof(u32)) {
m = le32_to_cpup(data);
v3 ^= m;
HSIPROUND;
v0 ^= m;
}
switch (left) {
case 3: b |= ((u32)end[2]) << 16;
case 2: b |= le16_to_cpup(data); break;
case 1: b |= end[0];
}
HPOSTAMBLE
}
EXPORT_SYMBOL(__hsiphash_aligned);
#ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
u32 __hsiphash_unaligned(const void *data, size_t len,
const hsiphash_key_t *key)
{
const u8 *end = data + len - (len % sizeof(u32));
const u8 left = len & (sizeof(u32) - 1);
u32 m;
HPREAMBLE(len)
for (; data != end; data += sizeof(u32)) {
m = get_unaligned_le32(data);
v3 ^= m;
HSIPROUND;
v0 ^= m;
}
switch (left) {
case 3: b |= ((u32)end[2]) << 16;
case 2: b |= get_unaligned_le16(end); break;
case 1: b |= end[0];
}
HPOSTAMBLE
}
EXPORT_SYMBOL(__hsiphash_unaligned);
#endif
/**
* hsiphash_1u32 - compute 32-bit hsiphash PRF value of a u32
* @first: first u32
* @key: the hsiphash key
*/
u32 hsiphash_1u32(const u32 first, const hsiphash_key_t *key)
{
HPREAMBLE(4)
v3 ^= first;
HSIPROUND;
v0 ^= first;
HPOSTAMBLE
}
EXPORT_SYMBOL(hsiphash_1u32);
/**
* hsiphash_2u32 - compute 32-bit hsiphash PRF value of 2 u32
* @first: first u32
* @second: second u32
* @key: the hsiphash key
*/
u32 hsiphash_2u32(const u32 first, const u32 second, const hsiphash_key_t *key)
{
HPREAMBLE(8)
v3 ^= first;
HSIPROUND;
v0 ^= first;
v3 ^= second;
HSIPROUND;
v0 ^= second;
HPOSTAMBLE
}
EXPORT_SYMBOL(hsiphash_2u32);
/**
* hsiphash_3u32 - compute 32-bit hsiphash PRF value of 3 u32
* @first: first u32
* @second: second u32
* @third: third u32
* @key: the hsiphash key
*/
u32 hsiphash_3u32(const u32 first, const u32 second, const u32 third,
const hsiphash_key_t *key)
{
HPREAMBLE(12)
v3 ^= first;
HSIPROUND;
v0 ^= first;
v3 ^= second;
HSIPROUND;
v0 ^= second;
v3 ^= third;
HSIPROUND;
v0 ^= third;
HPOSTAMBLE
}
EXPORT_SYMBOL(hsiphash_3u32);
/**
* hsiphash_4u32 - compute 32-bit hsiphash PRF value of 4 u32
* @first: first u32
* @second: second u32
* @third: third u32
* @forth: forth u32
* @key: the hsiphash key
*/
u32 hsiphash_4u32(const u32 first, const u32 second, const u32 third,
const u32 forth, const hsiphash_key_t *key)
{
HPREAMBLE(16)
v3 ^= first;
HSIPROUND;
v0 ^= first;
v3 ^= second;
HSIPROUND;
v0 ^= second;
v3 ^= third;
HSIPROUND;
v0 ^= third;
v3 ^= forth;
HSIPROUND;
v0 ^= forth;
HPOSTAMBLE
}
EXPORT_SYMBOL(hsiphash_4u32);
#endif
......@@ -7,7 +7,9 @@
* SipHash: a fast short-input PRF
* https://131002.net/siphash/
*
* This implementation is specifically for SipHash2-4.
* This implementation is specifically for SipHash2-4 for a secure PRF
* and HalfSipHash1-3/SipHash1-3 for an insecure PRF only suitable for
* hashtables.
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
......@@ -18,8 +20,8 @@
#include <linux/errno.h>
#include <linux/module.h>
/* Test vectors taken from official reference source available at:
* https://131002.net/siphash/siphash24.c
/* Test vectors taken from reference source available at:
* https://github.com/veorq/SipHash
*/
static const siphash_key_t test_key_siphash =
......@@ -50,6 +52,64 @@ static const u64 test_vectors_siphash[64] = {
0x958a324ceb064572ULL
};
#if BITS_PER_LONG == 64
static const hsiphash_key_t test_key_hsiphash =
{{ 0x0706050403020100ULL, 0x0f0e0d0c0b0a0908ULL }};
static const u32 test_vectors_hsiphash[64] = {
0x050fc4dcU, 0x7d57ca93U, 0x4dc7d44dU,
0xe7ddf7fbU, 0x88d38328U, 0x49533b67U,
0xc59f22a7U, 0x9bb11140U, 0x8d299a8eU,
0x6c063de4U, 0x92ff097fU, 0xf94dc352U,
0x57b4d9a2U, 0x1229ffa7U, 0xc0f95d34U,
0x2a519956U, 0x7d908b66U, 0x63dbd80cU,
0xb473e63eU, 0x8d297d1cU, 0xa6cce040U,
0x2b45f844U, 0xa320872eU, 0xdae6c123U,
0x67349c8cU, 0x705b0979U, 0xca9913a5U,
0x4ade3b35U, 0xef6cd00dU, 0x4ab1e1f4U,
0x43c5e663U, 0x8c21d1bcU, 0x16a7b60dU,
0x7a8ff9bfU, 0x1f2a753eU, 0xbf186b91U,
0xada26206U, 0xa3c33057U, 0xae3a36a1U,
0x7b108392U, 0x99e41531U, 0x3f1ad944U,
0xc8138825U, 0xc28949a6U, 0xfaf8876bU,
0x9f042196U, 0x68b1d623U, 0x8b5114fdU,
0xdf074c46U, 0x12cc86b3U, 0x0a52098fU,
0x9d292f9aU, 0xa2f41f12U, 0x43a71ed0U,
0x73f0bce6U, 0x70a7e980U, 0x243c6d75U,
0xfdb71513U, 0xa67d8a08U, 0xb7e8f148U,
0xf7a644eeU, 0x0f1837f2U, 0x4b6694e0U,
0xb7bbb3a8U
};
#else
static const hsiphash_key_t test_key_hsiphash =
{{ 0x03020100U, 0x07060504U }};
static const u32 test_vectors_hsiphash[64] = {
0x5814c896U, 0xe7e864caU, 0xbc4b0e30U,
0x01539939U, 0x7e059ea6U, 0x88e3d89bU,
0xa0080b65U, 0x9d38d9d6U, 0x577999b1U,
0xc839caedU, 0xe4fa32cfU, 0x959246eeU,
0x6b28096cU, 0x66dd9cd6U, 0x16658a7cU,
0xd0257b04U, 0x8b31d501U, 0x2b1cd04bU,
0x06712339U, 0x522aca67U, 0x911bb605U,
0x90a65f0eU, 0xf826ef7bU, 0x62512debU,
0x57150ad7U, 0x5d473507U, 0x1ec47442U,
0xab64afd3U, 0x0a4100d0U, 0x6d2ce652U,
0x2331b6a3U, 0x08d8791aU, 0xbc6dda8dU,
0xe0f6c934U, 0xb0652033U, 0x9b9851ccU,
0x7c46fb7fU, 0x732ba8cbU, 0xf142997aU,
0xfcc9aa1bU, 0x05327eb2U, 0xe110131cU,
0xf9e5e7c0U, 0xa7d708a6U, 0x11795ab1U,
0x65671619U, 0x9f5fff91U, 0xd89c5267U,
0x007783ebU, 0x95766243U, 0xab639262U,
0x9c7e1390U, 0xc368dda6U, 0x38ddc455U,
0xfa13d379U, 0x979ea4e8U, 0x53ecd77eU,
0x2ee80657U, 0x33dbb66aU, 0xae3f0577U,
0x88b4c4ccU, 0x3e7f480bU, 0x74c1ebf8U,
0x87178304U
};
#endif
static int __init siphash_test_init(void)
{
u8 in[64] __aligned(SIPHASH_ALIGNMENT);
......@@ -70,6 +130,16 @@ static int __init siphash_test_init(void)
pr_info("siphash self-test unaligned %u: FAIL\n", i + 1);
ret = -EINVAL;
}
if (hsiphash(in, i, &test_key_hsiphash) !=
test_vectors_hsiphash[i]) {
pr_info("hsiphash self-test aligned %u: FAIL\n", i + 1);
ret = -EINVAL;
}
if (hsiphash(in_unaligned + 1, i, &test_key_hsiphash) !=
test_vectors_hsiphash[i]) {
pr_info("hsiphash self-test unaligned %u: FAIL\n", i + 1);
ret = -EINVAL;
}
}
if (siphash_1u64(0x0706050403020100ULL, &test_key_siphash) !=
test_vectors_siphash[8]) {
......@@ -115,6 +185,28 @@ static int __init siphash_test_init(void)
pr_info("siphash self-test 4u32: FAIL\n");
ret = -EINVAL;
}
if (hsiphash_1u32(0x03020100U, &test_key_hsiphash) !=
test_vectors_hsiphash[4]) {
pr_info("hsiphash self-test 1u32: FAIL\n");
ret = -EINVAL;
}
if (hsiphash_2u32(0x03020100U, 0x07060504U, &test_key_hsiphash) !=
test_vectors_hsiphash[8]) {
pr_info("hsiphash self-test 2u32: FAIL\n");
ret = -EINVAL;
}
if (hsiphash_3u32(0x03020100U, 0x07060504U,
0x0b0a0908U, &test_key_hsiphash) !=
test_vectors_hsiphash[12]) {
pr_info("hsiphash self-test 3u32: FAIL\n");
ret = -EINVAL;
}
if (hsiphash_4u32(0x03020100U, 0x07060504U,
0x0b0a0908U, 0x0f0e0d0cU, &test_key_hsiphash) !=
test_vectors_hsiphash[16]) {
pr_info("hsiphash self-test 4u32: FAIL\n");
ret = -EINVAL;
}
if (!ret)
pr_info("self-tests: pass\n");
return ret;
......
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