man > EVP_KDF-TLS1_PRF(7SSL)

EVP_KDF-TLS1_PRF(7SSL)                         OpenSSL                        EVP_KDF-TLS1_PRF(7SSL)

NAME
       EVP_KDF-TLS1_PRF - The TLS1 PRF EVP_KDF implementation

DESCRIPTION
       Support for computing the TLS1 PRF through the EVP_KDF API.

       The EVP_KDF-TLS1_PRF algorithm implements the PRF used by TLS versions up to and including
       TLS 1.2.

   Identity
       "TLS1-PRF" is the name for this implementation; it can be used with the EVP_KDF_fetch()
       function.

   Supported parameters
       The supported parameters are:

       "properties" (OSSL_KDF_PARAM_PROPERTIES) <UTF8 string>
       "digest" (OSSL_KDF_PARAM_DIGEST) <UTF8 string>
           These parameters work as described in "PARAMETERS" in EVP_KDF(3).

           The OSSL_KDF_PARAM_DIGEST parameter is used to set the message digest associated with the
           TLS  PRF.  EVP_md5_sha1() 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.

       "secret" (OSSL_KDF_PARAM_SECRET) <octet string>
           This parameter sets the secret value of the  TLS  PRF.   Any  existing  secret  value  is
           replaced.

       "seed" (OSSL_KDF_PARAM_SEED) <octet string>
           This  parameter sets the context seed.  The length of the context seed cannot exceed 1024
           bytes; this should be more than enough for any normal use of the TLS PRF.

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

        EVP_KDF *kdf = EVP_KDF_fetch(NULL, "TLS1-PRF", NULL);
        EVP_KDF_CTX *kctx = EVP_KDF_CTX_new(kdf);

       The digest, secret value and seed must be set before a key is derived otherwise an error will
       occur.

       The output length of the PRF is specified by the keylen  parameter  to  the  EVP_KDF_derive()
       function.

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

        EVP_KDF *kdf;
        EVP_KDF_CTX *kctx;
        unsigned char out[10];
        OSSL_PARAM params[4], *p = params;

        kdf = EVP_KDF_fetch(NULL, "TLS1-PRF", NULL);
        kctx = EVP_KDF_CTX_new(kdf);
        EVP_KDF_free(kdf);

        *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_DIGEST,
                                                SN_sha256, strlen(SN_sha256));
        *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SECRET,
                                                 "secret", (size_t)6);
        *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SEED,
                                                 "seed", (size_t)4);
        *p = OSSL_PARAM_construct_end();
        if (EVP_KDF_derive(kctx, out, sizeof(out), params) <= 0) {
            error("EVP_KDF_derive");
        }
        EVP_KDF_CTX_free(kctx);

CONFORMING TO
       RFC 2246, RFC 5246 and NIST SP 800-135 r1

SEE ALSO
       EVP_KDF(3),     EVP_KDF_CTX_new(3),      EVP_KDF_CTX_free(3),      EVP_KDF_CTX_set_params(3),
       EVP_KDF_derive(3), "PARAMETERS" in EVP_KDF(3)

HISTORY
       This functionality was added in OpenSSL 3.0.

COPYRIGHT
       Copyright 2018-2021 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>.

3.0.13                                       2026-07-29                       EVP_KDF-TLS1_PRF(7SSL)