- NAME
- DESCRIPTION
  - ML-DSA Signature Parameters
- NOTES
- EXAMPLES
- SEE ALSO
- HISTORY
- COPYRIGHT

# NAME

EVP_SIGNATURE-ML-DSA, EVP_SIGNATURE-ML-DSA-44, EVP_SIGNATURE-ML-DSA-65, EVP_SIGNATURE-ML-DSA-87, - EVP_SIGNATURE ML-DSA support

# DESCRIPTION

The ML-DSA-44, ML-DSA-65 and ML-DSA-87 EVP_PKEY implementations support key generation, and one-shot sign and verify using the ML-DSA signature schemes described in FIPS 204.

The different algorithms names correspond to the parameter sets defined in FIPS 204 Section 4 Table 1. (The signatures range in size from ~2.5K to ~4.5K depending on the type chosen). There are 3 different security categories also depending on the type.

EVP_SIGNATURE_fetch(3) can be used to explicitly fetch one of the 3 algorithms which can then be used with EVP_PKEY_sign_message_init(3), EVP_PKEY_sign(3), EVP_PKEY_verify_message_init(3), and EVP_PKEY_verify(3) to perform one-shot message signing or signature verification.

The normal signing process (called Pure ML-DSA Signature Generation) encodes the message internally as 0x00 || len(ctx) || ctx || message. where ctx is some optional value of size 0x00..0xFF. This process is defined in FIPS 204 Algorithm 2 step 10 and Algorithm 3 step 5. OpenSSL also allows the message to not be encoded which is required for testing. OpenSSL does not support Pre Hash ML-DSA Signature Generation, but this may be done by the user by doing Pre hash encoding externally and then choosing the option to not encode the message.

## ML-DSA Signature Parameters

The following parameter can be used for both signing and verification. it may be set by passing an OSSL_PARAM array to EVP_PKEY_sign_message_init(3) or EVP_PKEY_verify_message_init(3)

"context-string" (OSSL_SIGNATURE_PARAM_CONTEXT_STRING) <octet string>

  A string of octets with length at most 255. By default it is the empty string.

The following parameters can be used when signing: They can be set by passing an OSSL_PARAM array to EVP_PKEY_sign_init_ex2(3).

"message-encoding" (OSSL_SIGNATURE_PARAM_MESSAGE_ENCODING) <integer>

  The default value of 1 uses 'Pure ML-DSA Signature Generation' as described above. Setting it to 0 does not encode the message, which is used for testing. The message encoding steps are defined in FIPS 204 Algorithm 2 step 10 and Algorithm 3 step 5.

"test-entropy" (OSSL_SIGNATURE_PARAM_TEST_ENTROPY) <octet string>

  Used for testing to pass an optional deterministic per message random value. If set the size must be 32 bytes.

"deterministic" (OSSL_SIGNATURE_PARAM_DETERMINISTIC) <integer>

  The default value of 0 causes the per message randomness to be randomly generated using a DRBG. Setting this to 1 causes the per message randomness to be set to 32 bytes of zeros. This value is ignored if "test-entropy" is set.

"mu" (OSSL_SIGNATURE_PARAM_MU) <integer>

  The default value of 0 causes sign and verify operations to process a raw message. Setting this to 1 causes those operations to assume the input is the `mu` value from FIPS 204 Algorithm 7 step 6 and Algorithm 8 step 7.

  Note that the message encoding steps from FIPS 204 Algorithm 2 step 10 and Algorithm 3 step 5 are omitted when this setting is 1.

See EVP_PKEY-ML-DSA(7) for information related to ML-DSA keys.

# NOTES

For backwards compatibility reasons EVP_DigestSignInit_ex(), EVP_DigestSign(), EVP_DigestVerifyInit_ex() and EVP_DigestVerify() may also be used, but the digest passed in mdname must be NULL.

# EXAMPLES

To sign a message using an ML-DSA EVP_PKEY structure:

    void do_sign(EVP_PKEY *key, unsigned char *msg, size_t msg_len)
    {
        size_t sig_len;
        unsigned char *sig = NULL;
        const OSSL_PARAM params[] = {
            OSSL_PARAM_octet_string("context-string", (unsigned char *)"A context string", 16),
            OSSL_PARAM_END
        };
        EVP_PKEY_CTX *sctx = EVP_PKEY_CTX_new_from_pkey(NULL, pkey, NULL);
        EVP_SIGNATURE *sig_alg = EVP_SIGNATURE_fetch(NULL, "ML-DSA-65", NULL);

        EVP_PKEY_sign_message_init(sctx, sig_alg, params);
        /* Calculate the required size for the signature by passing a NULL buffer. */
        EVP_PKEY_sign(sctx, NULL, &sig_len, msg, msg_len);
        sig = OPENSSL_zalloc(sig_len);
        EVP_PKEY_sign(sctx, sig, &sig_len, msg, msg_len);
        ...
        OPENSSL_free(sig);
        EVP_SIGNATURE_free(sig_alg);
        EVP_PKEY_CTX_free(sctx);
    }

# SEE ALSO

EVP_PKEY-ML-DSA(7) provider-signature(7), EVP_PKEY_sign(3), EVP_PKEY_verify(3), FIPS 204

# HISTORY

This functionality was added in OpenSSL 3.5.

# COPYRIGHT

Copyright 2025 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at https://www.openssl.org/source/license.html.