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fwtpm: reject ML-DSA signing with no private seed #643

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Merged
dgarske merged 1 commit into from
Oct 22, 2026
Merged

fwtpm: reject ML-DSA signing with no private seed #643

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15 changes: 15 additions & 0 deletions src/fwtpm/fwtpm_command.c
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Original file line number Diff line number Diff line change
Expand Up @@ -18910,6 +18910,14 @@ static TPM_RC FwCmd_SignSequenceComplete(FWTPM_CTX* ctx, TPM2_Packet* cmd,
if (rc == 0 && !(keyObj->pub.objectAttributes & TPMA_OBJECT_sign)) {
rc = TPM_RC_KEY;
}
/* Reject a public-only ML-DSA object: its all-zero seed derives a
* universally reproducible key. Checked here rather than at
* SequenceStart because a public-only twin shares the key's Name. */
if (rc == 0 && (keyObj->pub.type == TPM_ALG_MLDSA ||
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keyObj->pub.type == TPM_ALG_HASH_MLDSA) &&
keyObj->privKeySize != MAX_MLDSA_PRIV_SEED_SIZE) {
rc = TPM_RC_KEY;
}
/* Part 3 Sec.20.6.1: the x509sign attribute of keyHandle MUST NOT be SET
* (TPM_RC_ATTRIBUTES). Keys with x509sign restrict what digests can be
* signed for X.509 cert use; SignSequenceComplete is not the right
Expand Down Expand Up @@ -19576,6 +19584,13 @@ static TPM_RC FwCmd_SignDigest(FWTPM_CTX* ctx, TPM2_Packet* cmd, int cmdSize,
if (rc == 0 && !(obj->pub.objectAttributes & TPMA_OBJECT_sign)) {
rc = TPM_RC_KEY;
}
/* Reject a public-only ML-DSA object: its all-zero seed derives a
* universally reproducible key. */
if (rc == 0 && (obj->pub.type == TPM_ALG_MLDSA ||
obj->pub.type == TPM_ALG_HASH_MLDSA) &&
obj->privKeySize != MAX_MLDSA_PRIV_SEED_SIZE) {
rc = TPM_RC_KEY;
}

/* Part 3 Sec.20.7.1: x509sign restricts the key to X.509-cert signing
* and is rejected outright here with TPM_RC_ATTRIBUTES. Restricted
Expand Down
121 changes: 121 additions & 0 deletions tests/fwtpm_unit_tests.c
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Original file line number Diff line number Diff line change
Expand Up @@ -6072,6 +6072,126 @@ static void test_fwtpm_mldsa_quote_public_only_returns_key(void)
}
#endif /* WOLFTPM_MLDSA_SIGN && WOLFTPM_MLDSA_VERIFY && !FWTPM_NO_ATTESTATION */

/* LoadExternal a public-only ML-DSA-44 (or Hash-ML-DSA-44/SHA-256) signing
* key and return its handle. */
static UINT32 LoadPublicOnlyMldsa(FWTPM_CTX* ctx, UINT16 algType)
{
int rspSize = 0, pos = 0, pubStart;

PutU16BE(gCmd + pos, TPM_ST_NO_SESSIONS); pos += 2;
PutU32BE(gCmd + pos, 0); pos += 4;
PutU32BE(gCmd + pos, TPM_CC_LoadExternal); pos += 4;
PutU16BE(gCmd + pos, 0); pos += 2; /* inPrivate empty */
pubStart = pos;
PutU16BE(gCmd + pos, 0); pos += 2; /* size placeholder */
PutU16BE(gCmd + pos, algType); pos += 2; /* type */
PutU16BE(gCmd + pos, TPM_ALG_SHA256); pos += 2; /* nameAlg */
PutU32BE(gCmd + pos, 0x00040040); pos += 4; /* sign|userWithAuth */
PutU16BE(gCmd + pos, 0); pos += 2; /* authPolicy */
PutU16BE(gCmd + pos, TPM_MLDSA_44); pos += 2; /* parameterSet */
if (algType == TPM_ALG_HASH_MLDSA) {
PutU16BE(gCmd + pos, TPM_ALG_SHA256); pos += 2; /* hashAlg */
}
else {
gCmd[pos++] = NO; /* allowExternalMu */
}
PutU16BE(gCmd + pos, sizeof(gNistMldsa44Pk)); pos += 2;
memcpy(gCmd + pos, gNistMldsa44Pk, sizeof(gNistMldsa44Pk));
pos += sizeof(gNistMldsa44Pk);
PutU16BE(gCmd + pubStart, (UINT16)(pos - pubStart - 2));
PutU32BE(gCmd + pos, TPM_RH_NULL); pos += 4; /* hierarchy */
PutU32BE(gCmd + 2, (UINT32)pos);
AssertIntEQ(FWTPM_ProcessCommand(ctx, gCmd, pos, gRsp, &rspSize, 0),
TPM_RC_SUCCESS);
AssertIntEQ(GetRspRC(gRsp), TPM_RC_SUCCESS);
return GetU32BE(gRsp + TPM2_HEADER_SIZE);
}

/* A public-only ML-DSA key has no private seed. SignSequenceComplete and
* SignDigest must return TPM_RC_KEY rather than sign from an all-zero seed. */
static void test_fwtpm_mldsa_sign_public_only_returns_key(void)
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{
FWTPM_CTX ctx;
int rspSize, pos;
UINT32 handle, seqHandle;

memset(&ctx, 0, sizeof(ctx));
AssertIntEQ(fwtpm_test_startup(&ctx), 0);

handle = LoadPublicOnlyMldsa(&ctx, TPM_ALG_MLDSA);

/* SignSequenceStart (no auth, empty context) */
pos = 0;
PutU16BE(gCmd + pos, TPM_ST_NO_SESSIONS); pos += 2;
PutU32BE(gCmd + pos, 0); pos += 4;
PutU32BE(gCmd + pos, TPM_CC_SignSequenceStart); pos += 4;
PutU32BE(gCmd + pos, handle); pos += 4;
PutU16BE(gCmd + pos, 0); pos += 2;
PutU16BE(gCmd + pos, 0); pos += 2;
PutU32BE(gCmd + 2, (UINT32)pos);
rspSize = 0;
AssertIntEQ(FWTPM_ProcessCommand(&ctx, gCmd, pos, gRsp, &rspSize, 0),
TPM_RC_SUCCESS);
AssertIntEQ(GetRspRC(gRsp), TPM_RC_SUCCESS);
seqHandle = GetU32BE(gRsp + TPM2_HEADER_SIZE);

/* SignSequenceComplete must refuse: no private seed. */
pos = 0;
PutU16BE(gCmd + pos, TPM_ST_SESSIONS); pos += 2;
PutU32BE(gCmd + pos, 0); pos += 4;
PutU32BE(gCmd + pos, TPM_CC_SignSequenceComplete); pos += 4;
PutU32BE(gCmd + pos, seqHandle); pos += 4;
PutU32BE(gCmd + pos, handle); pos += 4;
PutU32BE(gCmd + pos, 18); pos += 4;
PutU32BE(gCmd + pos, TPM_RS_PW); pos += 4;
PutU16BE(gCmd + pos, 0); pos += 2;
gCmd[pos++] = 0; PutU16BE(gCmd + pos, 0); pos += 2;
PutU32BE(gCmd + pos, TPM_RS_PW); pos += 4;
PutU16BE(gCmd + pos, 0); pos += 2;
gCmd[pos++] = 0; PutU16BE(gCmd + pos, 0); pos += 2;
PutU16BE(gCmd + pos, 4); pos += 2; /* buffer */
memset(gCmd + pos, 0xAA, 4); pos += 4;
PutU32BE(gCmd + 2, (UINT32)pos);
rspSize = 0;
AssertIntEQ(FWTPM_ProcessCommand(&ctx, gCmd, pos, gRsp, &rspSize, 0),
TPM_RC_SUCCESS);
AssertIntEQ(GetRspRC(gRsp), TPM_RC_KEY);

FlushHandle(&ctx, seqHandle);
FlushHandle(&ctx, handle);

#ifdef WOLFTPM_HASH_MLDSA
handle = LoadPublicOnlyMldsa(&ctx, TPM_ALG_HASH_MLDSA);

/* SignDigest must refuse: no private seed. */
pos = 0;
PutU16BE(gCmd + pos, TPM_ST_SESSIONS); pos += 2;
PutU32BE(gCmd + pos, 0); pos += 4;
PutU32BE(gCmd + pos, TPM_CC_SignDigest); pos += 4;
PutU32BE(gCmd + pos, handle); pos += 4;
PutU32BE(gCmd + pos, 9); pos += 4;
PutU32BE(gCmd + pos, TPM_RS_PW); pos += 4;
PutU16BE(gCmd + pos, 0); pos += 2;
gCmd[pos++] = 0; PutU16BE(gCmd + pos, 0); pos += 2;
PutU16BE(gCmd + pos, 0); pos += 2; /* context empty */
PutU16BE(gCmd + pos, 32); pos += 2; /* digest */
memset(gCmd + pos, 0xAA, 32); pos += 32;
PutU16BE(gCmd + pos, TPM_ST_HASHCHECK); pos += 2;
PutU32BE(gCmd + pos, TPM_RH_NULL); pos += 4;
PutU16BE(gCmd + pos, 0); pos += 2;
PutU32BE(gCmd + 2, (UINT32)pos);
rspSize = 0;
AssertIntEQ(FWTPM_ProcessCommand(&ctx, gCmd, pos, gRsp, &rspSize, 0),
TPM_RC_SUCCESS);
AssertIntEQ(GetRspRC(gRsp), TPM_RC_KEY);

FlushHandle(&ctx, handle);
#endif /* WOLFTPM_HASH_MLDSA */

FWTPM_Cleanup(&ctx);
fwtpm_pass("MLDSA sign public-only key rejected:", 1);
}

/* TPM2_LoadExternal must reject ML public areas with an unsupported parameter
* set, an out-of-range allowExternalMu, an invalid Hash-ML-DSA hash, invalid
* ML-KEM symmetric parameters, or a public key size inconsistent with the
Expand Down Expand Up @@ -19140,6 +19260,7 @@ int fwtpm_unit_tests(int argc, char *argv[])
test_fwtpm_signseqcomplete_truncated_buffer();
test_fwtpm_verifyseqcomplete_neg();
test_fwtpm_signdigest_neg();
test_fwtpm_mldsa_sign_public_only_returns_key();
#ifdef WOLFTPM_HASH_MLDSA
test_fwtpm_signdigest_malformed_hashcheck_tag();
test_fwtpm_signdigest_restricted_null_ticket_returns_ticket();
Expand Down
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