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.IX Title "EVP_PKEY_CTX_SET_TLS1_PRF_MD 3"
.TH EVP_PKEY_CTX_SET_TLS1_PRF_MD 3 "2023-09-11" "1.1.1w" "OpenSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.nh
.SH "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
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #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);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
The \fB\s-1EVP_PKEY_TLS1_PRF\s0\fR algorithm implements the \s-1PRF\s0 key derivation function for
\&\s-1TLS.\s0 It has no associated private key and only implements key derivation
using \fBEVP_PKEY_derive\fR\|(3).
.PP
\&\fBEVP_PKEY_set_tls1_prf_md()\fR sets the message digest associated with the
\&\s-1TLS PRF.\s0 \fBEVP_md5_sha1()\fR is treated as a special case which uses the \s-1PRF\s0
algorithm using both \fB\s-1MD5\s0\fR and \fB\s-1SHA1\s0\fR as used in \s-1TLS 1.0\s0 and 1.1.
.PP
\&\fBEVP_PKEY_CTX_set_tls1_prf_secret()\fR sets the secret value of the \s-1TLS PRF\s0
to \fBseclen\fR bytes of the buffer \fBsec\fR. Any existing secret value is replaced
and any seed is reset.
.PP
\&\fBEVP_PKEY_CTX_add1_tls1_prf_seed()\fR sets the seed to \fBseedlen\fR bytes of \fBseed\fR.
If a seed is already set it is appended to the existing value.
.SH "STRING CTRLS"
.IX Header "STRING CTRLS"
The \s-1TLS PRF\s0 also supports string based control operations using
\&\fBEVP_PKEY_CTX_ctrl_str\fR\|(3).
The \fBtype\fR parameter \*(L"md\*(R" uses the supplied \fBvalue\fR as the name of the digest
algorithm to use.
The \fBtype\fR parameters \*(L"secret\*(R" and \*(L"seed\*(R" use the supplied \fBvalue\fR parameter
as a secret or seed value.
The names \*(L"hexsecret\*(R" and \*(L"hexseed\*(R" are similar except they take a hex string
which is converted to binary.
.SH "NOTES"
.IX Header "NOTES"
All these functions are implemented as macros.
.PP
A context for the \s-1TLS PRF\s0 can be obtained by calling:
.PP
.Vb 1
\& EVP_PKEY_CTX *pctx = EVP_PKEY_CTX_new_id(EVP_PKEY_TLS1_PRF, NULL);
.Ve
.PP
The digest, secret value and seed must be set before a key is derived or an
error occurs.
.PP
The total length of all seeds cannot exceed 1024 bytes in length: this should
be more than enough for any normal use of the \s-1TLS PRF.\s0
.PP
The output length of the \s-1PRF\s0 is specified by the length parameter in the
\&\fBEVP_PKEY_derive()\fR function. Since the output length is variable, setting
the buffer to \fB\s-1NULL\s0\fR is not meaningful for the \s-1TLS PRF.\s0
.PP
Optimised versions of the \s-1TLS PRF\s0 can be implemented in an \s-1ENGINE.\s0
.SH "RETURN VALUES"
.IX Header "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.
.SH "EXAMPLES"
.IX Header "EXAMPLES"
This example derives 10 bytes using \s-1SHA\-256\s0 with the secret key \*(L"secret\*(R"
and seed value \*(L"seed\*(R":
.PP
.Vb 3
\& 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 */
.Ve
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBEVP_PKEY_CTX_new\fR\|(3),
\&\fBEVP_PKEY_CTX_ctrl_str\fR\|(3),
\&\fBEVP_PKEY_derive\fR\|(3)
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright 2016\-2019 The OpenSSL Project Authors. All Rights Reserved.
.PP
Licensed under the OpenSSL license (the \*(L"License\*(R").  You may not use
this file except in compliance with the License.  You can obtain a copy
in the file \s-1LICENSE\s0 in the source distribution or at
<https://www.openssl.org/source/license.html>.