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Add documentation for EVP_PKEY_TLS1_PRF

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Reviewed-by: Matt Caswell <matt@openssl.org>
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Dr. Stephen Henson 2016-01-19 13:59:09 +00:00
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doc/crypto/EVP_PKEY_TLS1_PRF.pod Normal file
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=pod
=head1 NAME
EVP_PKEY_TLS1_PRF, 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
=head1 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, seed, seedlen)
unsigned char *seed, int seedlen);
=head1 DESCRIPTION
The EVP_PKEY_TLS1_PRF algorithm implements the PRF key derivation function for
TLS. It has no associated private key and only implements key derivation
using EVP_PKEY_derive().
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 both B<MD5> and B<SHA1> as used in TLS 1.0 and 1.1.
EVP_PKEY_CTX_set_tls1_prf_secret() sets the secret value of the TLS PRF
to B<seclen> bytes of the buffer B<sec>. Any existing secret value is replaced
and any seed is reset.
EVP_PKEY_CTX_add1_tls1_prf_seed() sets the seed to B<seedlen> bytes of B<seed>.
If a seed is already set it is appended to the existing value.
=head1 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_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 the
EVP_PKEY_derive() function. Since the output length is variable, setting
the buffer to B<NULL> is not meaningful for the TLS PRF.
Optimised versions of the TLS PRF can be implemented in an ENGINE.
=head1 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.
=head1 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 */
=head1 SEE ALSO
L<EVP_PKEY_CTX_new(3)>,
L<EVP_PKEY_derive(3)>,
=cut