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.\" ========================================================================
.\"
.IX Title "EVP_KDF-SS 7"
.TH EVP_KDF-SS 7 "2023-05-07" "3.0.9" "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\-SS \- The Single Step / One Step EVP_KDF implementation
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
The \s-1EVP_KDF\-SS\s0 algorithm implements the Single Step key derivation function (\s-1SSKDF\s0).
\&\s-1SSKDF\s0 derives a key using input such as a shared secret key (that was generated
during the execution of a key establishment scheme) and fixedinfo.
\&\s-1SSKDF\s0 is also informally referred to as 'Concat \s-1KDF\s0'.
.SS "Auxiliary function"
.IX Subsection "Auxiliary function"
The implementation uses a selectable auxiliary function H, which can be one of:
.IP "\fBH(x) = hash(x, digest=md)\fR" 4
.IX Item "H(x) = hash(x, digest=md)"
.PD 0
.IP "\fBH(x) = HMAC_hash(x, key=salt, digest=md)\fR" 4
.IX Item "H(x) = HMAC_hash(x, key=salt, digest=md)"
.ie n .IP "\fBH(x) = KMACxxx(x, key=salt, custom=""\s-1KDF"",\s0 outlen=mac_size)\fR" 4
.el .IP "\fBH(x) = KMACxxx(x, key=salt, custom=``\s-1KDF'',\s0 outlen=mac_size)\fR" 4
.IX Item "H(x) = KMACxxx(x, key=salt, custom=KDF, outlen=mac_size)"
.PD
.PP
Both the \s-1HMAC\s0 and \s-1KMAC\s0 implementations set the key using the 'salt' value.
The hash and \s-1HMAC\s0 also require the digest to be set.
.SS "Identity"
.IX Subsection "Identity"
\&\*(L"\s-1SSKDF\*(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
This parameter is ignored for \s-1KMAC.\s0
.ie n .IP """mac"" (\fB\s-1OSSL_KDF_PARAM_MAC\s0\fR) <\s-1UTF8\s0 string>" 4
.el .IP "``mac'' (\fB\s-1OSSL_KDF_PARAM_MAC\s0\fR) <\s-1UTF8\s0 string>" 4
.IX Item "mac (OSSL_KDF_PARAM_MAC) <UTF8 string>"
.PD 0
.ie n .IP """maclen"" (\fB\s-1OSSL_KDF_PARAM_MAC_SIZE\s0\fR) <unsigned integer>" 4
.el .IP "``maclen'' (\fB\s-1OSSL_KDF_PARAM_MAC_SIZE\s0\fR) <unsigned integer>" 4
.IX Item "maclen (OSSL_KDF_PARAM_MAC_SIZE) <unsigned integer>"
.ie n .IP """salt"" (\fB\s-1OSSL_KDF_PARAM_SALT\s0\fR) <octet string>" 4
.el .IP "``salt'' (\fB\s-1OSSL_KDF_PARAM_SALT\s0\fR) <octet string>" 4
.IX Item "salt (OSSL_KDF_PARAM_SALT) <octet string>"
.PD
These parameters work as described in \*(L"\s-1PARAMETERS\*(R"\s0 in \s-1\fBEVP_KDF\s0\fR\|(3).
.ie n .IP """key"" (\fB\s-1EVP_KDF_CTRL_SET_KEY\s0\fR) <octet string>" 4
.el .IP "``key'' (\fB\s-1EVP_KDF_CTRL_SET_KEY\s0\fR) <octet string>" 4
.IX Item "key (EVP_KDF_CTRL_SET_KEY) <octet string>"
This parameter set the shared secret that is used for key derivation.
.ie n .IP """info"" (\fB\s-1OSSL_KDF_PARAM_INFO\s0\fR) <octet string>" 4
.el .IP "``info'' (\fB\s-1OSSL_KDF_PARAM_INFO\s0\fR) <octet string>" 4
.IX Item "info (OSSL_KDF_PARAM_INFO) <octet string>"
This parameter sets an optional value for fixedinfo, also known as otherinfo.
.SH "NOTES"
.IX Header "NOTES"
A context for \s-1SSKDF\s0 can be obtained by calling:
.PP
.Vb 2
\& EVP_KDF *kdf = EVP_KDF_fetch(NULL, "SSKDF", NULL);
\& EVP_KDF_CTX *kctx = EVP_KDF_CTX_new(kdf);
.Ve
.PP
The output length of an \s-1SSKDF\s0 is specified via the \fIkeylen\fR
parameter to the \fBEVP_KDF_derive\fR\|(3) function.
.SH "EXAMPLES"
.IX Header "EXAMPLES"
This example derives 10 bytes using H(x) = \s-1SHA\-256,\s0 with the secret key \*(L"secret\*(R"
and fixedinfo value \*(L"label\*(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, "SSKDF", 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_KEY,
\&                                          "secret", (size_t)6);
\& *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_INFO,
\&                                          "label", (size_t)5);
\& *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
.PP
This example derives 10 bytes using H(x) = \s-1HMAC\s0(\s-1SHA\-256\s0), with the secret key \*(L"secret\*(R",
fixedinfo value \*(L"label\*(R" and salt \*(L"salt\*(R":
.PP
.Vb 4
\& EVP_KDF *kdf;
\& EVP_KDF_CTX *kctx;
\& unsigned char out[10];
\& OSSL_PARAM params[6], *p = params;
\&
\& kdf = EVP_KDF_fetch(NULL, "SSKDF", NULL);
\& kctx = EVP_KDF_CTX_new(kdf);
\& EVP_KDF_free(kdf);
\&
\& *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_MAC,
\&                                         SN_hmac, strlen(SN_hmac));
\& *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_DIGEST,
\&                                         SN_sha256, strlen(SN_sha256));
\& *p++ = OSSL_PARAM_construct_octet_string(EVP_KDF_CTRL_SET_KEY,
\&                                          "secret", (size_t)6);
\& *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_INFO,
\&                                          "label", (size_t)5);
\& *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SALT,
\&                                          "salt", (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
.PP
This example derives 10 bytes using H(x) = \s-1KMAC128\s0(x,salt,outlen), with the secret key \*(L"secret\*(R"
fixedinfo value \*(L"label\*(R", salt of \*(L"salt\*(R" and \s-1KMAC\s0 outlen of 20:
.PP
.Vb 4
\& EVP_KDF *kdf;
\& EVP_KDF_CTX *kctx;
\& unsigned char out[10];
\& OSSL_PARAM params[6], *p = params;
\&
\& kdf = EVP_KDF_fetch(NULL, "SSKDF", NULL);
\& kctx = EVP_KDF_CTX_new(kdf);
\& EVP_KDF_free(kdf);
\&
\& *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_MAC,
\&                                         SN_kmac128, strlen(SN_kmac128));
\& *p++ = OSSL_PARAM_construct_octet_string(EVP_KDF_CTRL_SET_KEY,
\&                                          "secret", (size_t)6);
\& *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_INFO,
\&                                          "label", (size_t)5);
\& *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SALT,
\&                                          "salt", (size_t)4);
\& *p++ = OSSL_PARAM_construct_size_t(OSSL_KDF_PARAM_MAC_SIZE, (size_t)20);
\& *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-1NIST\s0 SP800\-56Cr1.
.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\-2023 The OpenSSL Project Authors. All Rights Reserved.  Copyright
(c) 2019, Oracle and/or its affiliates.  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>.