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



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>.



3.0.12                            2023-05-07               EVP_KDF-TLS1_PRF(7)