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**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/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**

TheEVP_PKEY_TLS1_PRFalgorithm implements the PRF key derivation function for TLS. It has no associated private key and only implements key derivation usingEVP_PKEY_derive(3).EVP_PKEY_set_tls1_prf_md()sets the message digest associated with the TLS PRF.EVP_md5_sha1()is treated as a special case which uses the PRF algorithm using bothMD5andSHA1as used in TLS 1.0 and 1.1.EVP_PKEY_CTX_set_tls1_prf_secret()sets the secret value of the TLS PRF toseclenbytes of the buffersec. Any existing secret value is replaced and any seed is reset.EVP_PKEY_CTX_add1_tls1_prf_seed()sets the seed toseedlenbytes ofseed. If a seed is already set it is appended to the existing value.

**STRING** **CTRLS**

The TLS PRF also supports string based control operations usingEVP_PKEY_CTX_ctrl_str(3). Thetypeparameter "md" uses the suppliedvalueas the name of the digest algorithm to use. Thetypeparameters "secret" and "seed" use the suppliedvalueparameter 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 theEVP_PKEY_derive()function. Since the output length is variable, setting the buffer toNULLis not meaningful for the TLS PRF. Optimised versions of the TLS PRF can be implemented in an ENGINE.

**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.

**EXAMPLE**

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_new(3),EVP_PKEY_CTX_ctrl_str(3),EVP_PKEY_derive(3)

**COPYRIGHT**

Copyright 2016 The OpenSSL Project Authors. All Rights Reserved. Licensed under the OpenSSL license (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>.