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Avoid calling keccak_absorb with partial lanes #450

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Avoid calling keccak_absorb with partial lanes #450

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d1d5113
Avoid calling keccak_absorb with partial lanes
bremoran Sep 10, 2025
aa57a15
Fix pos reset, fix linting errors
bremoran Sep 10, 2025
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59 changes: 52 additions & 7 deletions mldsa/sign.c
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Original file line number Diff line number Diff line change
Expand Up @@ -208,6 +208,50 @@ int crypto_sign_keypair(uint8_t *pk, uint8_t *sk)
return result;
}

static void shake256_absorb_with_residual(keccak_state *state,
const uint8_t *in, size_t inlen,
uint8_t *residual, size_t *pos)
__contract__(
requires(0 <= *pos && pos <= 8)
requires(memory_no_alias(state, sizeof(uint64_t) * MLD_KECCAK_LANES))
requires(in == NULL || memory_no_alias(in, inlen))
requires(memory_no_alias(residual, 8))
assigns(memory_slice(state, sizeof(uint64_t) * MLD_KECCAK_LANES))
assigns(memory_slice(residual, 8))
assigns(*pos)
)
{
size_t nb;
if (in)
{
if (*pos)
{
nb = inlen < 8 - *pos ? inlen : 8 - *pos;
memcpy(residual + *pos, in, nb);
inlen -= nb;
in += nb;
*pos += nb;
if (*pos == 8)
{
shake256_absorb(state, residual, 8U);
*pos = 0;
}
}
nb = inlen & ~7UL;
if (nb)
{
shake256_absorb(state, in, nb);
in += nb;
inlen -= nb;
}
if (inlen)
{
memcpy(residual, in, inlen);
*pos = inlen;
}
}
}

/*************************************************
* Name: mld_H
*
Expand Down Expand Up @@ -243,21 +287,22 @@ __contract__(
)
{
keccak_state state;
uint8_t buf[8];
size_t pos = 0;
shake256_init(&state);
shake256_absorb(&state, in1, in1len);
if (in2 != NULL)
{
shake256_absorb(&state, in2, in2len);
}
if (in3 != NULL)
shake256_absorb_with_residual(&state, in1, in1len, buf, &pos);
shake256_absorb_with_residual(&state, in2, in2len, buf, &pos);
shake256_absorb_with_residual(&state, in3, in3len, buf, &pos);
if (pos)
{
shake256_absorb(&state, in3, in3len);
shake256_absorb(&state, buf, pos);
}
shake256_finalize(&state);
shake256_squeeze(out, outlen, &state);

/* FIPS 204. Section 3.6.3 Destruction of intermediate values. */
mld_zeroize(&state, sizeof(state));
mld_zeroize(&buf, sizeof(buf));
}

/* Reference: The reference implementation does not explicitly */
Expand Down
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