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Reject invalid API inputs before unsafe work #1231

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ec5c1b7
Reject invalid API inputs before unsafe work
fegge Jun 26, 2026
395184d
Address API input validation review feedback
fegge Jun 30, 2026
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10 changes: 5 additions & 5 deletions mldsa/mldsa_native.h
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Original file line number Diff line number Diff line change
Expand Up @@ -360,7 +360,7 @@ int MLD_API_NAMESPACE(signature_internal)(
* @param[in] m Pointer to message to be signed.
* @param mlen Length of message.
* @param[in] ctx Pointer to context string. May be NULL if ctxlen == 0.
* @param ctxlen Length of context string. Should be <= 255.
* @param ctxlen Length of context string. Must be <= 255.
* @param[in] sk Bit-packed secret key.
* @param context Application context. Only present when
* MLD_CONFIG_CONTEXT_PARAMETER is defined; type set by
Expand Down Expand Up @@ -437,8 +437,8 @@ int MLD_API_NAMESPACE(signature_extmu)(
* @param[out] smlen Pointer to output length of signed message.
* @param[in] m Pointer to message to be signed.
* @param mlen Length of message.
* @param[in] ctx Pointer to context string.
* @param ctxlen Length of context string.
* @param[in] ctx Pointer to context string. May be NULL if ctxlen == 0.
* @param ctxlen Length of context string. Must be <= 255.
* @param[in] sk Bit-packed secret key.
* @param context Application context. Only present when
* MLD_CONFIG_CONTEXT_PARAMETER is defined; type set by
Expand Down Expand Up @@ -835,8 +835,8 @@ int MLD_API_NAMESPACE(verify_pre_hash_shake256)(
* @param[in] ph Pointer to pre-hashed message (ignored for pure
* ML-DSA).
* @param phlen Length of pre-hashed message (ignored for pure ML-DSA).
* @param[in] ctx Pointer to context string (may be NULL).
* @param ctxlen Length of context string.
* @param[in] ctx Pointer to context string. May be NULL if ctxlen == 0.
* @param ctxlen Length of context string. Must be <= 255.
* @param hashalg Hash algorithm constant (MLD_PREHASH_NONE for pure
* ML-DSA, or MLD_PREHASH_* for HashML-DSA).
*
Expand Down
36 changes: 34 additions & 2 deletions mldsa/src/sign.c
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Original file line number Diff line number Diff line change
Expand Up @@ -915,6 +915,7 @@ int mld_sign_signature_internal(uint8_t sig[MLDSA_CRYPTO_BYTES], size_t *siglen,
uint8_t *rho, *tr, *key, *mu, *rhoprime;
uint16_t nonce = 0;
const uint16_t nonce_limit = mld_get_max_signing_attempts();

MLD_ALLOC(seedbuf, uint8_t,
2 * MLDSA_SEEDBYTES + MLDSA_TRBYTES + 2 * MLDSA_CRHBYTES, context);
MLD_ALLOC(mat, mld_polymat, 1, context);
Expand All @@ -929,6 +930,12 @@ int mld_sign_signature_internal(uint8_t sig[MLDSA_CRYPTO_BYTES], size_t *siglen,
goto cleanup;
}

if (externalmu && mlen != MLDSA_CRHBYTES)
{
ret = MLD_ERR_FAIL;
goto cleanup;
}

rho = seedbuf;
tr = rho + MLDSA_SEEDBYTES;
key = tr + MLDSA_TRBYTES;
Expand Down Expand Up @@ -1052,6 +1059,7 @@ int mld_sign_signature(uint8_t sig[MLDSA_CRYPTO_BYTES], size_t *siglen,
{
size_t pre_len;
int ret;

MLD_ALLOC(pre, uint8_t, MLD_DOMAIN_SEPARATION_MAX_BYTES, context);
MLD_ALLOC(rnd, uint8_t, MLDSA_RNDBYTES, context);
Comment on lines +1062 to 1064

@hanno-becker hanno-becker Jun 27, 2026

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The check must happen after the allocations for strict C90 compliance. Which has the benefit that we can reuse the cleanup section.


Expand All @@ -1061,6 +1069,12 @@ int mld_sign_signature(uint8_t sig[MLDSA_CRYPTO_BYTES], size_t *siglen,
goto cleanup;
}

if (ctxlen > 255 || (ctx == NULL && ctxlen != 0))

@mkannwischer mkannwischer Jul 16, 2026

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Please remove the ctx == NULL check throughout.
We are not checking for NULL pointers anywhere else in the code.
I'll separately open a PR to document the convention to not check for NULL.

{
ret = MLD_ERR_FAIL;
goto cleanup;
}

/* Prepare domain separation prefix for pure ML-DSA */
pre_len = mld_prepare_domain_separation_prefix(pre, NULL, 0, ctx, ctxlen,
MLD_PREHASH_NONE);
Expand Down Expand Up @@ -1204,7 +1218,7 @@ int mld_sign_verify_internal(const uint8_t *sig, size_t siglen,
goto cleanup;
}

if (siglen != MLDSA_CRYPTO_BYTES)
if (siglen != MLDSA_CRYPTO_BYTES || (externalmu && mlen != MLDSA_CRHBYTES))
{
ret = MLD_ERR_FAIL;
goto cleanup;
Expand Down Expand Up @@ -1320,6 +1334,12 @@ int mld_sign_verify(const uint8_t *sig, size_t siglen, const uint8_t *m,
size_t pre_len;
int ret;

if (ctxlen > 255 || (ctx == NULL && ctxlen != 0))
{
ret = MLD_ERR_FAIL;
goto cleanup;
}

pre_len = mld_prepare_domain_separation_prefix(pre, NULL, 0, ctx, ctxlen,
MLD_PREHASH_NONE);
if (pre_len == 0)
Expand Down Expand Up @@ -1411,6 +1431,12 @@ int mld_sign_signature_pre_hash_internal(
size_t pre_len;
int ret;

if (ctxlen > 255 || (ctx == NULL && ctxlen != 0))
{
ret = MLD_ERR_FAIL;
goto cleanup;
}

pre_len = mld_prepare_domain_separation_prefix(pre, ph, phlen, ctx, ctxlen,
hashalg);
if (pre_len == 0)
Expand Down Expand Up @@ -1453,6 +1479,12 @@ int mld_sign_verify_pre_hash_internal(
size_t pre_len;
int ret;

if (ctxlen > 255 || (ctx == NULL && ctxlen != 0))
{
ret = MLD_ERR_FAIL;
goto cleanup;
}

pre_len = mld_prepare_domain_separation_prefix(pre, ph, phlen, ctx, ctxlen,
hashalg);
if (pre_len == 0)
Expand Down Expand Up @@ -1607,7 +1639,7 @@ size_t mld_prepare_domain_separation_prefix(
uint8_t prefix[MLD_DOMAIN_SEPARATION_MAX_BYTES], const uint8_t *ph,
size_t phlen, const uint8_t *ctx, size_t ctxlen, int hashalg)
{
if (ctxlen > 255)
if (ctxlen > 255 || (ctx == NULL && ctxlen != 0))

@hanno-becker hanno-becker Jun 27, 2026

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I'd prefer input validation to happen at the top-level API, even if it means a bit of code-duplication.

{
return 0;
}
Expand Down
12 changes: 6 additions & 6 deletions mldsa/src/sign.h
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Original file line number Diff line number Diff line change
Expand Up @@ -253,7 +253,7 @@ __contract__(
* @param[in] m Pointer to message to be signed.
* @param mlen Length of message.
* @param[in] ctx Pointer to context string. May be NULL if ctxlen == 0.
* @param ctxlen Length of context string. Should be <= 255.
* @param ctxlen Length of context string. Must be <= 255.
* @param[in] sk Bit-packed secret key.
* @param context Application context. Only present when
* MLD_CONFIG_CONTEXT_PARAMETER is defined; type set by
Expand Down Expand Up @@ -343,8 +343,8 @@ __contract__(
* @param[out] smlen Pointer to output length of signed message.
* @param[in] m Pointer to message to be signed.
* @param mlen Length of message.
* @param[in] ctx Pointer to context string.
* @param ctxlen Length of context string.
* @param[in] ctx Pointer to context string. May be NULL if ctxlen == 0.
* @param ctxlen Length of context string. Must be <= 255.
* @param[in] sk Bit-packed secret key.
* @param context Application context. Only present when
* MLD_CONFIG_CONTEXT_PARAMETER is defined; type set by
Expand All @@ -371,7 +371,7 @@ __contract__(
requires(memory_no_alias(smlen, sizeof(size_t)))
requires(m == sm || memory_no_alias(m, mlen))
requires(ctxlen <= MLD_MAX_BUFFER_SIZE)
requires(memory_no_alias(ctx, ctxlen))
requires(ctxlen == 0 || memory_no_alias(ctx, ctxlen))

@mkannwischer mkannwischer Jul 17, 2026

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I am not sure if this needed. My understanding was that memory_no_alias() does permit NULL if the length is zero bytes.
@hanno-becker?

requires(memory_no_alias(sk, MLDSA_CRYPTO_SECRETKEYBYTES))
assigns(memory_slice(sm, MLDSA_CRYPTO_BYTES + mlen))
assigns(object_whole(smlen))
Expand Down Expand Up @@ -787,8 +787,8 @@ __contract__(
* @param[in] ph Pointer to pre-hashed message (ignored for pure
* ML-DSA).
* @param phlen Length of pre-hashed message (ignored for pure ML-DSA).
* @param[in] ctx Pointer to context string (may be NULL).
* @param ctxlen Length of context string.
* @param[in] ctx Pointer to context string. May be NULL if ctxlen == 0.
* @param ctxlen Length of context string. Must be <= 255.
* @param hashalg Hash algorithm constant (MLD_PREHASH_NONE for pure
* ML-DSA, or MLD_PREHASH_* for HashML-DSA).
*
Expand Down
4 changes: 2 additions & 2 deletions test/src/test_alloc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -517,16 +517,16 @@ int main(void)
r |= test_pk_from_sk_alloc_failure(&ctx);
#endif

/* Sign tests */
#if !defined(MLD_CONFIG_NO_SIGN_API)
/* Sign tests */
r |= test_sign_alloc_failure(&ctx);
r |= test_sign_combined_alloc_failure(&ctx);
r |= test_signature_extmu_alloc_failure(&ctx);
r |= test_signature_pre_hash_shake256_alloc_failure(&ctx);
#endif /* !MLD_CONFIG_NO_SIGN_API */

/* Verify tests */
#if !defined(MLD_CONFIG_NO_VERIFY_API)
/* Verify tests */
r |= test_verify_alloc_failure(&ctx);
r |= test_verify_extmu_alloc_failure(&ctx);
r |= test_verify_pre_hash_shake256_alloc_failure(&ctx);
Expand Down
46 changes: 46 additions & 0 deletions test/src/test_mldsa.c
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Expand Up @@ -13,6 +13,8 @@

/* Additional SUPERCOP-style macros for functions not in the standard set */
#define crypto_sign_keypair_internal MLD_API_NAMESPACE(keypair_internal)
#define crypto_sign_signature_internal MLD_API_NAMESPACE(signature_internal)
#define crypto_sign_verify_internal MLD_API_NAMESPACE(verify_internal)
#define crypto_sign_signature_extmu MLD_API_NAMESPACE(signature_extmu)
#define crypto_sign_verify_extmu MLD_API_NAMESPACE(verify_extmu)
#define crypto_sign_signature_pre_hash_shake256 \
Expand Down Expand Up @@ -134,6 +136,49 @@ static int test_sign_unaligned(void)
return test_sign_core(pk + 1, sk + 1, sm + 1, m + 1, m2 + 1, ctx + 1);
}

static int test_invalid_inputs_rejected(void)
{
uint8_t pk[CRYPTO_PUBLICKEYBYTES];
uint8_t sk[CRYPTO_SECRETKEYBYTES];
uint8_t sig[CRYPTO_BYTES];
uint8_t m[MLEN];
uint8_t mu[MLDSA_CRHBYTES];
uint8_t rnd[MLDSA_RNDBYTES];
size_t siglen = CRYPTO_BYTES;
int rc;

CHECK(crypto_sign_keypair(pk, sk) == 0);
CHECK(randombytes(m, sizeof(m)) == 0);
MLD_CT_TESTING_SECRET(m, sizeof(m));
CHECK(randombytes(mu, sizeof(mu)) == 0);
MLD_CT_TESTING_SECRET(mu, sizeof(mu));
CHECK(randombytes(rnd, sizeof(rnd)) == 0);
MLD_CT_TESTING_SECRET(rnd, sizeof(rnd));
CHECK(randombytes(sig, sizeof(sig)) == 0);
MLD_CT_TESTING_SECRET(sig, sizeof(sig));

rc = crypto_sign_signature(sig, &siglen, m, sizeof(m), NULL, 1, sk);
CHECK(rc == MLD_ERR_FAIL);
CHECK(siglen == 0);

siglen = CRYPTO_BYTES;
rc = crypto_sign_signature_internal(sig, &siglen, mu, MLDSA_CRHBYTES - 1,
NULL, 0, rnd, sk, 1);
CHECK(rc == MLD_ERR_FAIL);
CHECK(siglen == 0);

rc = crypto_sign_verify(sig, CRYPTO_BYTES, m, sizeof(m), NULL, 1, pk);
CHECK(rc == MLD_ERR_FAIL);
rc = crypto_sign_verify_internal(sig, CRYPTO_BYTES - 1, mu, sizeof(mu), NULL,
0, pk, 1);
CHECK(rc == MLD_ERR_FAIL);
rc = crypto_sign_verify_internal(sig, CRYPTO_BYTES, mu, MLDSA_CRHBYTES - 1,
NULL, 0, pk, 1);
CHECK(rc == MLD_ERR_FAIL);

return 0;
}

static int test_sign_extmu(void)
{
uint8_t pk[CRYPTO_PUBLICKEYBYTES];
Expand Down Expand Up @@ -509,6 +554,7 @@ int main(void)
!defined(MLD_CONFIG_NO_VERIFY_API)
r |= test_sign();
r |= test_sign_unaligned();
r |= test_invalid_inputs_rejected();
r |= test_wrong_pk();
r |= test_wrong_sig();
r |= test_wrong_ctx();
Expand Down