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Merged
mkannwischer merged 2 commits into from
Apr 17, 2026
Merged

Sign: Set smlen to 0 in case of failure #959

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bdc1b8a
sign: Set smlen to 0 in case of failure
mkannwischer Feb 10, 2026
1c2e573
CT: Clarify that t0 is public despite it not being part of the pk
mkannwischer Feb 10, 2026
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11 changes: 8 additions & 3 deletions mldsa/src/sign.c
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Original file line number Diff line number Diff line change
Expand Up @@ -720,8 +720,10 @@ __contract__(
* Consequently, any value that can be computed from the signature and public
* key is considered public.
* w0 and w1 are public as they can be computed from Az - ct = \alpha w1 + w0.
* h=c*t0 is public as both c and t0 are public.
* For a more detailed discussion, refer to https://eprint.iacr.org/2022/1406.
* h=c*t0 is public as both c and t0 are considered public.
* While t0 is not part of the public key, it can be reconstructed from
* a small number of signatures and need not be regarded as secret
* (see @[FIPS204, Section 6.1]).
*/
MLD_CT_TESTING_DECLASSIFY(w0, sizeof(*w0));
MLD_CT_TESTING_DECLASSIFY(w1, sizeof(*w1));
Expand Down Expand Up @@ -1012,7 +1014,10 @@ int mld_sign(uint8_t *sm, size_t *smlen, const uint8_t *m, size_t mlen,
}
ret = mld_sign_signature(sm, smlen, sm + MLDSA_CRYPTO_BYTES, mlen, ctx,
ctxlen, sk, context);
*smlen += mlen;
if (ret == 0)
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{
*smlen += mlen;
}
return ret;
}
#endif /* !MLD_CONFIG_NO_RANDOMIZED_API */
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6 changes: 3 additions & 3 deletions mldsa/src/sign.h
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Original file line number Diff line number Diff line change
Expand Up @@ -353,9 +353,9 @@ __contract__(
assigns(memory_slice(sm, MLDSA_CRYPTO_BYTES + mlen))
assigns(object_whole(smlen))
ensures((return_value == 0 && *smlen == MLDSA_CRYPTO_BYTES + mlen) ||
(return_value == MLD_ERR_FAIL
|| return_value == MLD_ERR_OUT_OF_MEMORY
|| return_value == MLD_ERR_RNG_FAIL))
((return_value == MLD_ERR_FAIL
|| return_value == MLD_ERR_OUT_OF_MEMORY
|| return_value == MLD_ERR_RNG_FAIL) && *smlen == 0))
);
#endif /* !MLD_CONFIG_CORE_API_ONLY */
#endif /* !MLD_CONFIG_NO_SIGN_API */
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