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Code Issues 1 Releases Wiki Activity

Use siphash for string hashing.

Browse Source 
The hash key still needs to randomly initialized
for the security advantage, but this patch is a
step closer to avoiding hash based DOS.

Further work may including exposing the raw hash
function for use by abstract types who also choose to
implement hash.
This commit is contained in:
Andrew Chambers 2020-01-17 11:52:29 +13:00
parent 962cd7e5f5
commit ea02b2fde9
2 changed files with 102 additions and 5 deletions
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106
src/core/util.c
View File

@ -94,14 +94,110 @@ const char *const janet_status_names[16] = {
"alive"
};
/*
Public domain siphash implementation sourced from:
https://raw.githubusercontent.com/veorq/SipHash/master/halfsiphash.c
We have made a few alterations, such as hardcoding the output size
and then removing dead code.
*/
#define cROUNDS 2
#define dROUNDS 4
#define ROTL(x, b) (uint32_t)(((x) << (b)) | ((x) >> (32 - (b))))
#define U8TO32_LE(p) \
(((uint32_t)((p)[0])) | ((uint32_t)((p)[1]) << 8) | \
((uint32_t)((p)[2]) << 16) | ((uint32_t)((p)[3]) << 24))
#define SIPROUND \
do { \
v0 += v1; \
v1 = ROTL(v1, 5); \
v1 ^= v0; \
v0 = ROTL(v0, 16); \
v2 += v3; \
v3 = ROTL(v3, 8); \
v3 ^= v2; \
v0 += v3; \
v3 = ROTL(v3, 7); \
v3 ^= v0; \
v2 += v1; \
v1 = ROTL(v1, 13); \
v1 ^= v2; \
v2 = ROTL(v2, 16); \
} while (0)
static uint32_t halfsiphash(const uint8_t *in, const size_t inlen, const uint8_t *k) {
uint32_t v0 = 0;
uint32_t v1 = 0;
uint32_t v2 = UINT32_C(0x6c796765);
uint32_t v3 = UINT32_C(0x74656462);
uint32_t k0 = U8TO32_LE(k);
uint32_t k1 = U8TO32_LE(k + 4);
uint32_t m;
int i;
const uint8_t *end = in + inlen - (inlen % sizeof(uint32_t));
const int left = inlen & 3;
uint32_t b = ((uint32_t)inlen) << 24;
v3 ^= k1;
v2 ^= k0;
v1 ^= k1;
v0 ^= k0;
for (; in != end; in += 4) {
m = U8TO32_LE(in);
v3 ^= m;
for (i = 0; i < cROUNDS; ++i)
SIPROUND;
v0 ^= m;
}
switch (left) {
case 3:
b |= ((uint32_t)in[2]) << 16;
case 2:
b |= ((uint32_t)in[1]) << 8;
case 1:
b |= ((uint32_t)in[0]);
break;
case 0:
break;
}
v3 ^= b;
for (i = 0; i < cROUNDS; ++i)
SIPROUND;
v0 ^= b;
v2 ^= 0xff;
for (i = 0; i < dROUNDS; ++i)
SIPROUND;
b = v1 ^ v3;
return b;
}
/* end of siphash */
static uint8_t hash_key[16] = {0};
void janet_init_hash_key(uint8_t new_key[16]) {
memcpy(hash_key, new_key, sizeof(hash_key));
}
/* Calculate hash for string */
int32_t janet_string_calchash(const uint8_t *str, int32_t len) {
const uint8_t *end = str + len;
uint32_t hash = 5381;
while (str < end)
hash = (hash << 5) + hash + *str++;
return (int32_t) hash;
uint32_t hash;
hash = halfsiphash(str, len, hash_key);
return (int32_t)hash;
}
/* Computes hash of an array of values */

1
src/include/janet.h
View File

@ -1303,6 +1303,7 @@ JANET_API JanetBuffer *janet_pretty(JanetBuffer *buffer, int depth, int flags, J
/* Misc */
JANET_API int janet_equals(Janet x, Janet y);
JANET_API void janet_init_hash_key(uint8_t key[16]);
JANET_API int32_t janet_hash(Janet x);
JANET_API int janet_compare(Janet x, Janet y);
JANET_API int janet_cstrcmp(JanetString str, const char *other);