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)

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>.