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.\" ========================================================================
.\"
.IX Title "EVP_KDF-TLS1_PRF 7ossl"
.TH EVP_KDF-TLS1_PRF 7ossl "2025-09-30" "3.5.4" "OpenSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
EVP_KDF\-TLS1_PRF \- The TLS1 PRF EVP_KDF implementation
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
Support for computing the \fB\s-1TLS1\s0\fR \s-1PRF\s0 through the \fB\s-1EVP_KDF\s0\fR \s-1API.\s0
.PP
The \s-1EVP_KDF\-TLS1_PRF\s0 algorithm implements the \s-1PRF\s0 used by \s-1TLS\s0 versions up to
and including \s-1TLS 1.2.\s0
.PP
The output is considered to be keying material.
.SS "Identity"
.IX Subsection "Identity"
\&\*(L"\s-1TLS1\-PRF\*(R"\s0 is the name for this implementation; it
can be used with the \fBEVP_KDF_fetch()\fR function.
.SS "Supported parameters"
.IX Subsection "Supported parameters"
The supported parameters are:
.ie n .IP """properties"" (\fB\s-1OSSL_KDF_PARAM_PROPERTIES\s0\fR) <\s-1UTF8\s0 string>" 4
.el .IP "``properties'' (\fB\s-1OSSL_KDF_PARAM_PROPERTIES\s0\fR) <\s-1UTF8\s0 string>" 4
.IX Item "properties (OSSL_KDF_PARAM_PROPERTIES) <UTF8 string>"
.PD 0
.ie n .IP """digest"" (\fB\s-1OSSL_KDF_PARAM_DIGEST\s0\fR) <\s-1UTF8\s0 string>" 4
.el .IP "``digest'' (\fB\s-1OSSL_KDF_PARAM_DIGEST\s0\fR) <\s-1UTF8\s0 string>" 4
.IX Item "digest (OSSL_KDF_PARAM_DIGEST) <UTF8 string>"
.PD
These parameters work as described in \*(L"\s-1PARAMETERS\*(R"\s0 in \s-1\fBEVP_KDF\s0\fR\|(3).
.Sp
The \fB\s-1OSSL_KDF_PARAM_DIGEST\s0\fR parameter is used to set 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.
.ie n .IP """secret"" (\fB\s-1OSSL_KDF_PARAM_SECRET\s0\fR) <octet string>" 4
.el .IP "``secret'' (\fB\s-1OSSL_KDF_PARAM_SECRET\s0\fR) <octet string>" 4
.IX Item "secret (OSSL_KDF_PARAM_SECRET) <octet string>"
This parameter sets the secret value of the \s-1TLS PRF.\s0
Any existing secret value is replaced.
.ie n .IP """seed"" (\fB\s-1OSSL_KDF_PARAM_SEED\s0\fR) <octet string>" 4
.el .IP "``seed'' (\fB\s-1OSSL_KDF_PARAM_SEED\s0\fR) <octet string>" 4
.IX Item "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 \s-1TLS PRF.\s0
.PP
The OpenSSL \s-1FIPS\s0 provider also supports the following parameters:
.ie n .IP """fips-indicator"" (\fB\s-1OSSL_KDF_PARAM_FIPS_APPROVED_INDICATOR\s0\fR) <integer>" 4
.el .IP "``fips-indicator'' (\fB\s-1OSSL_KDF_PARAM_FIPS_APPROVED_INDICATOR\s0\fR) <integer>" 4
.IX Item "fips-indicator (OSSL_KDF_PARAM_FIPS_APPROVED_INDICATOR) <integer>"
A getter that returns 1 if the operation is \s-1FIPS\s0 approved, or 0 otherwise.
This may be used after calling EVP_KDF_derive. It returns 0 if any \*(L"***\-check\*(R"
related parameter is set to 0 and the check fails.
.ie n .IP """ems_check"" (\fB\s-1OSSL_KDF_PARAM_FIPS_EMS_CHECK\s0\fR) <integer>" 4
.el .IP "``ems_check'' (\fB\s-1OSSL_KDF_PARAM_FIPS_EMS_CHECK\s0\fR) <integer>" 4
.IX Item "ems_check (OSSL_KDF_PARAM_FIPS_EMS_CHECK) <integer>"
The default value of 1 causes an error during \fBEVP_KDF_derive()\fR if
\&\*(L"master secret\*(R" is used instead of \*(L"extended master secret\*(R" Setting this to zero
will ignore the error and set the approved \*(L"fips-indicator\*(R" to 0.
This option breaks \s-1FIPS\s0 compliance if it causes the approved \*(L"fips-indicator\*(R"
to return 0.
.ie n .IP """digest-check"" (\fB\s-1OSSL_KDF_PARAM_FIPS_DIGEST_CHECK\s0\fR) <integer>" 4
.el .IP "``digest-check'' (\fB\s-1OSSL_KDF_PARAM_FIPS_DIGEST_CHECK\s0\fR) <integer>" 4
.IX Item "digest-check (OSSL_KDF_PARAM_FIPS_DIGEST_CHECK) <integer>"
The default value of 1 causes an error during \fBEVP_KDF_CTX_set_params()\fR if
used digest is not approved.
Setting this to zero will ignore the error and set the approved
\&\*(L"fips-indicator\*(R" to 0.
This option breaks \s-1FIPS\s0 compliance if it causes the approved \*(L"fips-indicator\*(R"
to return 0.
.Sp
According to \s-1SP\s0 800\-135r1, the following are approved digest algorithms:
\&\s-1SHA2\-256, SHA2\-384, SHA2\-512.\s0
.ie n .IP """key-check"" (\fB\s-1OSSL_KDF_PARAM_FIPS_KEY_CHECK\s0\fR) <integer>" 4
.el .IP "``key-check'' (\fB\s-1OSSL_KDF_PARAM_FIPS_KEY_CHECK\s0\fR) <integer>" 4
.IX Item "key-check (OSSL_KDF_PARAM_FIPS_KEY_CHECK) <integer>"
The default value of 1 causes an error during \fBEVP_KDF_CTX_set_params()\fR if the
length of used key-derivation key (\fB\s-1OSSL_KDF_PARAM_SECRET\s0\fR) is shorter than 112
bits.
Setting this to zero will ignore the error and set the approved
\&\*(L"fips-indicator\*(R" to 0.
This option breaks \s-1FIPS\s0 compliance if it causes the approved \*(L"fips-indicator\*(R"
to return 0.
.SH "NOTES"
.IX Header "NOTES"
A context for the \s-1TLS PRF\s0 can be obtained by calling:
.PP
.Vb 2
\& EVP_KDF *kdf = EVP_KDF_fetch(NULL, "TLS1\-PRF", NULL);
\& EVP_KDF_CTX *kctx = EVP_KDF_CTX_new(kdf);
.Ve
.PP
The digest, secret value and seed must be set before a key is derived otherwise
an error will occur.
.PP
The output length of the \s-1PRF\s0 is specified by the \fIkeylen\fR parameter to the
\&\fBEVP_KDF_derive()\fR function.
.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 4
\& 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);
.Ve
.SH "CONFORMING TO"
.IX Header "CONFORMING TO"
\&\s-1RFC 2246, RFC 5246\s0 and \s-1NIST SP 800\-135\s0 r1
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\s-1\fBEVP_KDF\s0\fR\|(3),
\&\fBEVP_KDF_CTX_new\fR\|(3),
\&\fBEVP_KDF_CTX_free\fR\|(3),
\&\fBEVP_KDF_CTX_set_params\fR\|(3),
\&\fBEVP_KDF_derive\fR\|(3),
\&\*(L"\s-1PARAMETERS\*(R"\s0 in \s-1\fBEVP_KDF\s0\fR\|(3)
.SH "HISTORY"
.IX Header "HISTORY"
This functionality was added in OpenSSL 3.0.
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright 2018\-2024 The OpenSSL Project Authors. All Rights Reserved.
.PP
Licensed under the Apache License 2.0 (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>.
