EVP_PKEY_CTX_set_tls1_prf_md (3)

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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

The algorithm implements the key derivation function for 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

EVP_md5_sha1() is treated as a special case which uses the algorithm using both and as used in and 1.1.

EVP_PKEY_CTX_set_tls1_prf_secret() sets the secret value of the

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 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

can be obtained by calling:

 EVP_PKEY_CTX *pctx = EVP_PKEY_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

The output length of the

is specified by the length parameter in the EVP_PKEY_derive() function. Since the output length is variable, setting the buffer to is not meaningful for the

Optimised versions of the

can be implemented in an

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 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

in the source distribution or at <www.openssl.org/source/license.html>.