EVP_PKEY_CTX_SET_TLS1_PRF_MD(3)                       Library Functions Manual

NAME
     EVP_PKEY_CTX_set_tls1_prf_md, EVP_PKEY_CTX_set1_tls1_prf_secret,
     EVP_PKEY_CTX_add1_tls1_prf_seed - TLS PRF key derivation algorithm

SYNOPSIS
     #include <openssl/evp.h>
     #include <openssl/kdf.h>

     int
     EVP_PKEY_CTX_set_tls1_prf_md(EVP_PKEY_CTX *pctx, const EVP_MD *md);

     int
     EVP_PKEY_CTX_set1_tls1_prf_secret(EVP_PKEY_CTX *pctx, unsigned char *sec,
         int seclen);

     int
     EVP_PKEY_CTX_add1_tls1_prf_seed(EVP_PKEY_CTX *pctx, unsigned char *seed,
         int seedlen);

DESCRIPTION
     The EVP_PKEY_TLS1_PRF algorithm implements the PRF key derivation
     function for TLS.  It has no associated private key and only implements
     key derivation using EVP_PKEY_derive(3).

     EVP_PKEY_set_tls1_prf_md() sets the message digest associated with the
     TLS PRF.  EVP_md5_sha1(3) is treated as a special case which uses the PRF
     algorithm using both MD5 and SHA1 as used in TLS 1.0 and 1.1.

     EVP_PKEY_CTX_set_tls1_prf_secret() sets the secret value of the TLS PRF
     to seclen bytes of the buffer sec.  Any existing secret value is replaced
     and any seed is reset.

     EVP_PKEY_CTX_add1_tls1_prf_seed() sets the seed to seedlen bytes of seed.
     If a seed is already set it is appended to the existing value.

STRING CTRLS
     The TLS PRF also supports string based control operations using
     EVP_PKEY_CTX_ctrl_str(3).  The type parameter "md" uses the supplied
     value as the name of the digest algorithm to use.  The type parameters
     "secret" and "seed" use the supplied value parameter as a secret or seed
     value.  The names "hexsecret" and "hexseed" are similar except they take
     a hex string which is converted to binary.

NOTES
     All these functions are implemented as macros.

     A context for the TLS PRF can be obtained by calling:

      EVP_PKEY_CTX *pctx = EVP_PKEY_CTX_new_id(EVP_PKEY_TLS1_PRF, NULL);

     The digest, secret value and seed must be set before a key is derived or
     an error occurs.

     The total length of all seeds cannot exceed 1024 bytes in length: this
     should be more than enough for any normal use of the TLS PRF.

     The output length of the PRF is specified by the length parameter in the
     EVP_PKEY_derive(3) function.  Since the output length is variable,
     setting the buffer to NULL is not meaningful for the TLS PRF.

RETURN VALUES
     All these functions return 1 for success and 0 or a negative value for
     failure.  In particular a return value of -2 indicates the operation is
     not supported by the public key algorithm.

EXAMPLES
     This example derives 10 bytes using SHA-256 with the secret key "secret"
     and seed value "seed":

      EVP_PKEY_CTX *pctx;
      unsigned char out[10];
      size_t outlen = sizeof(out);

      pctx = EVP_PKEY_CTX_new_id(EVP_PKEY_TLS1_PRF, NULL);
      if (EVP_PKEY_derive_init(pctx) <= 0)
          /* Error */
      if (EVP_PKEY_CTX_set_tls1_prf_md(pctx, EVP_sha256()) <= 0)
          /* Error */
      if (EVP_PKEY_CTX_set1_tls1_prf_secret(pctx, "secret", 6) <= 0)
          /* Error */
      if (EVP_PKEY_CTX_add1_tls1_prf_seed(pctx, "seed", 4) <= 0)
          /* Error */
      if (EVP_PKEY_derive(pctx, out, &outlen) <= 0)
          /* Error */

SEE ALSO
     EVP_PKEY_CTX_ctrl_str(3), EVP_PKEY_CTX_new(3), EVP_PKEY_derive(3)

HISTORY
     These functions first appeared in OpenSSL 1.1.0 and have been available
     since OpenBSD 7.6.

Linux 6.10.10-arch1-1            July 10, 2024           Linux 6.10.10-arch1-1