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secret generator v2

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update 128-bit scrambler at each 16-bytes round.
ensure there is no delta-correlation possible between segments,
even when the initial custom seed is poor (<= 16 bytes, or full of `\0` characters).
This commit is contained in:
Yann Collet 2020-06-04 21:23:05 -07:00
parent 4d0ec6e6ed
commit 58922a773b
2 changed files with 13 additions and 25 deletions
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36
xxh3.h
View File

@ -2032,33 +2032,19 @@ XXH3_generateSecret(void* secretBuffer, const void* customSeed, size_t customSee
memcpy(secretBuffer, XXH3_kSecret, XXH_SECRET_DEFAULT_SIZE);
return;
}
XXH_ASSERT(customSeed != NULL);
{ size_t const segmentSize = 16;
size_t const nbSeedSegments = (customSeedSize + (segmentSize-1)) % segmentSize;
size_t const nbSecretSegments = XXH_SECRET_DEFAULT_SIZE % segmentSize;
XXH128_hash_t const scrambler = XXH128(customSeed, customSeedSize, 0);
{ size_t const segmentSize = sizeof(XXH128_hash_t);
size_t const nbSegments = XXH_SECRET_DEFAULT_SIZE / segmentSize;
XXH128_hash_t scrambler = XXH128(customSeed, customSeedSize, 0);
size_t segnb;
for (segnb=0; segnb < nbSecretSegments; segnb++) {
size_t const secretSegmentStart = segnb * segmentSize;
size_t const seedSegmentSize = ((segnb % nbSeedSegments) == 0) ?
(customSeedSize % segmentSize) : segmentSize;
size_t const seedSegmentStart = (segnb % nbSeedSegments) * segmentSize;
XXH128_hash_t localSegment, seedSegment;
XXH_ASSERT(sizeof(localSegment) == segmentSize);
memset(&seedSegment, 0, segmentSize);
memcpy(&seedSegment, (const char*)customSeed + seedSegmentStart, seedSegmentSize);
memcpy(&localSegment, (const char*)XXH3_kSecret + secretSegmentStart, segmentSize);
/* endianess does not matter for this xor operation */
localSegment.low64 ^= seedSegment.low64;
localSegment.high64 ^= seedSegment.high64;
/* now endianess matter */
XXH_writeLE64(&localSegment.low64, XXH_readLE64(&localSegment.low64) + XXH_readLE64(&scrambler.low64));
XXH_writeLE64(&localSegment.high64, XXH_readLE64(&localSegment.high64) + XXH_readLE64(&scrambler.high64));
/* result */
memcpy((char*)secretBuffer + secretSegmentStart, &localSegment, segmentSize);
}
}
XXH_ASSERT(segmentSize * nbSegments == XXH_SECRET_DEFAULT_SIZE); /* exact multiple */
memcpy(secretBuffer, &scrambler, sizeof(scrambler));
for (segnb=1; segnb < nbSegments; segnb++) {
size_t const segmentStart = segnb * segmentSize;
scrambler = XXH128(&scrambler, sizeof(scrambler), 0);
memcpy((char*)secretBuffer + segmentStart, &scrambler, sizeof(scrambler));
} }
}

2
xxhash.h
View File

@ -497,6 +497,8 @@ struct XXH64_state_s {
# define XXH3_64bits_reset_withSecret XXH_NAME2(XXH_NAMESPACE, XXH3_64bits_reset_withSecret)
# define XXH3_64bits_update XXH_NAME2(XXH_NAMESPACE, XXH3_64bits_update)
# define XXH3_64bits_digest XXH_NAME2(XXH_NAMESPACE, XXH3_64bits_digest)
# define XXH3_generateSecret XXH_NAME2(XXH_NAMESPACE, XXH3_generateSecret)
#endif
/* XXH3_64bits():