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.\" ========================================================================
.\"
.IX Title "EVP_KDF-X942-ASN1 7"
.TH EVP_KDF-X942-ASN1 7 "2023-05-07" "3.0.9" "OpenSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.nh
.SH "NAME"
EVP_KDF\-X942\-ASN1 \- The X9.42\-2003 asn1 EVP_KDF implementation
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
The \s-1EVP_KDF\-X942\-ASN1\s0 algorithm implements the key derivation function
X942KDF\-ASN1. It is used by \s-1DH\s0 KeyAgreement, to derive a key using input such as
a shared secret key and other info. The other info is \s-1DER\s0 encoded data that
contains a 32 bit counter as well as optional fields for \*(L"partyu-info\*(R",
\&\*(L"partyv-info\*(R", \*(L"supp-pubinfo\*(R" and \*(L"supp-privinfo\*(R".
This kdf is used by Cryptographic Message Syntax (\s-1CMS\s0).
.SS "Identity"
.IX Subsection "Identity"
\&\*(L"X942KDF\-ASN1\*(R" or \*(L"X942KDF\*(R" 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).
.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>"
The shared secret used for key derivation.  This parameter sets the secret.
.ie n .IP """acvp-info"" (\fB\s-1OSSL_KDF_PARAM_X942_ACVPINFO\s0\fR) <octet string>" 4
.el .IP "``acvp-info'' (\fB\s-1OSSL_KDF_PARAM_X942_ACVPINFO\s0\fR) <octet string>" 4
.IX Item "acvp-info (OSSL_KDF_PARAM_X942_ACVPINFO) <octet string>"
This value should not be used in production and should only be used for \s-1ACVP\s0
testing. It is an optional octet string containing a combined \s-1DER\s0 encoded blob
of any of the optional fields related to \*(L"partyu-info\*(R", \*(L"partyv-info\*(R",
\&\*(L"supp-pubinfo\*(R" and \*(L"supp-privinfo\*(R". If it is specified then none of these other
fields should be used.
.ie n .IP """partyu-info"" (\fB\s-1OSSL_KDF_PARAM_X942_PARTYUINFO\s0\fR) <octet string>" 4
.el .IP "``partyu-info'' (\fB\s-1OSSL_KDF_PARAM_X942_PARTYUINFO\s0\fR) <octet string>" 4
.IX Item "partyu-info (OSSL_KDF_PARAM_X942_PARTYUINFO) <octet string>"
An optional octet string containing public info contributed by the initiator.
.ie n .IP """ukm"" (\fB\s-1OSSL_KDF_PARAM_UKM\s0\fR) <octet string>" 4
.el .IP "``ukm'' (\fB\s-1OSSL_KDF_PARAM_UKM\s0\fR) <octet string>" 4
.IX Item "ukm (OSSL_KDF_PARAM_UKM) <octet string>"
An alias for \*(L"partyu-info\*(R".
In \s-1CMS\s0 this is the user keying material.
.ie n .IP """partyv-info"" (\fB\s-1OSSL_KDF_PARAM_X942_PARTYVINFO\s0\fR) <octet string>" 4
.el .IP "``partyv-info'' (\fB\s-1OSSL_KDF_PARAM_X942_PARTYVINFO\s0\fR) <octet string>" 4
.IX Item "partyv-info (OSSL_KDF_PARAM_X942_PARTYVINFO) <octet string>"
An optional octet string containing public info contributed by the responder.
.ie n .IP """supp-pubinfo"" (\fB\s-1OSSL_KDF_PARAM_X942_SUPP_PUBINFO\s0\fR) <octet string>" 4
.el .IP "``supp-pubinfo'' (\fB\s-1OSSL_KDF_PARAM_X942_SUPP_PUBINFO\s0\fR) <octet string>" 4
.IX Item "supp-pubinfo (OSSL_KDF_PARAM_X942_SUPP_PUBINFO) <octet string>"
An optional octet string containing some additional, mutually-known public
information. Setting this value also sets \*(L"use-keybits\*(R" to 0.
.ie n .IP """use-keybits"" (\fB\s-1OSSL_KDF_PARAM_X942_USE_KEYBITS\s0\fR) <integer>" 4
.el .IP "``use-keybits'' (\fB\s-1OSSL_KDF_PARAM_X942_USE_KEYBITS\s0\fR) <integer>" 4
.IX Item "use-keybits (OSSL_KDF_PARAM_X942_USE_KEYBITS) <integer>"
The default value of 1 will use the \s-1KEK\s0 key length (in bits) as the
\&\*(L"supp-pubinfo\*(R". A value of 0 disables setting the \*(L"supp-pubinfo\*(R".
.ie n .IP """supp-privinfo"" (\fB\s-1OSSL_KDF_PARAM_X942_SUPP_PRIVINFO\s0\fR) <octet string>" 4
.el .IP "``supp-privinfo'' (\fB\s-1OSSL_KDF_PARAM_X942_SUPP_PRIVINFO\s0\fR) <octet string>" 4
.IX Item "supp-privinfo (OSSL_KDF_PARAM_X942_SUPP_PRIVINFO) <octet string>"
An optional octet string containing some additional, mutually-known private
information.
.ie n .IP """cekalg"" (\fB\s-1OSSL_KDF_PARAM_CEK_ALG\s0\fR) <\s-1UTF8\s0 string>" 4
.el .IP "``cekalg'' (\fB\s-1OSSL_KDF_PARAM_CEK_ALG\s0\fR) <\s-1UTF8\s0 string>" 4
.IX Item "cekalg (OSSL_KDF_PARAM_CEK_ALG) <UTF8 string>"
This parameter sets the \s-1CEK\s0 wrapping algorithm name.
Valid values are \*(L"\s-1AES\-128\-WRAP\*(R", \*(L"AES\-192\-WRAP\*(R", \*(L"AES\-256\-WRAP\*(R"\s0 and \*(L"\s-1DES3\-WRAP\*(R".\s0
.SH "NOTES"
.IX Header "NOTES"
A context for X942KDF can be obtained by calling:
.PP
.Vb 2
\& EVP_KDF *kdf = EVP_KDF_fetch(NULL, "X942KDF", NULL);
\& EVP_KDF_CTX *kctx = EVP_KDF_CTX_new(kdf);
.Ve
.PP
The output length of an X942KDF is specified via the \fIkeylen\fR
parameter to the \fBEVP_KDF_derive\fR\|(3) function.
.SH "EXAMPLES"
.IX Header "EXAMPLES"
This example derives 24 bytes, with the secret key \*(L"secret\*(R" and random user
keying material:
.PP
.Vb 5
\&  EVP_KDF_CTX *kctx;
\&  EVP_KDF_CTX *kctx;
\&  unsigned char out[192/8];
\&  unsignred char ukm[64];
\&  OSSL_PARAM params[5], *p = params;
\&
\&  if (RAND_bytes(ukm, sizeof(ukm)) <= 0)
\&      error("RAND_bytes");
\&
\&  kdf = EVP_KDF_fetch(NULL, "X942KDF", NULL);
\&  if (kctx == NULL)
\&      error("EVP_KDF_fetch");
\&  kctx = EVP_KDF_CTX_new(kdf);
\&  EVP_KDF_free(kdf);
\&  if (kctx == NULL)
\&      error("EVP_KDF_CTX_new");
\&
\&  *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_DIGEST, "SHA256", 0);
\&  *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SECRET,
\&                                           "secret", (size_t)6);
\&  *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_UKM, ukm, sizeof(ukm));
\&  *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_CEK_ALG, "AES\-256\-WRAP, 0);
\&  *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-1ANS1 X9.42\-2003
RFC 2631\s0
.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_CTX_get_kdf_size\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 2019\-2022 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>.