Path: blob/main/crypto/openssl/doc/man7/EVP_KDF-SS.pod
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=pod
=head1 NAME
EVP_KDF-SS - The Single Step / One Step EVP_KDF implementation
=head1 DESCRIPTION
The EVP_KDF-SS algorithm implements the Single Step key derivation function (SSKDF).
SSKDF derives a key using input such as a shared secret key (that was generated
during the execution of a key establishment scheme) and fixedinfo.
SSKDF is also informally referred to as 'Concat KDF'.
The output is considered to be keying material.
=head2 Auxiliary function
The implementation uses a selectable auxiliary function H, which can be one of:
=over 4
=item B<H(x) = hash(x, digest=md)>
=item B<H(x) = HMAC_hash(x, key=salt, digest=md)>
=item B<H(x) = KMACxxx(x, key=salt, custom="KDF", outlen=mac_size)>
=back
Both the HMAC and KMAC implementations set the key using the 'salt' value.
The hash and HMAC also require the digest to be set.
=head2 Identity
"SSKDF" is the name for this implementation; it
can be used with the EVP_KDF_fetch() function.
=head2 Supported parameters
The supported parameters are:
=over 4
=item "properties" (B<OSSL_KDF_PARAM_PROPERTIES>) <UTF8 string>
=item "digest" (B<OSSL_KDF_PARAM_DIGEST>) <UTF8 string>
This parameter is ignored for KMAC.
=item "mac" (B<OSSL_KDF_PARAM_MAC>) <UTF8 string>
=item "maclen" (B<OSSL_KDF_PARAM_MAC_SIZE>) <unsigned integer>
=item "salt" (B<OSSL_KDF_PARAM_SALT>) <octet string>
These parameters work as described in L<EVP_KDF(3)/PARAMETERS>.
=item "key" (B<OSSL_KDF_PARAM_SECRET>) <octet string>
This parameter set the shared secret that is used for key derivation.
=item "info" (B<OSSL_KDF_PARAM_INFO>) <octet string>
This parameter sets an optional value for fixedinfo, also known as otherinfo.
=back
The OpenSSL FIPS provider also supports the following parameters:
=over 4
=item "fips-indicator" (B<OSSL_KDF_PARAM_FIPS_APPROVED_INDICATOR>) <integer>
A getter that returns 1 if the operation is FIPS approved, or 0 otherwise.
This may be used after calling EVP_KDF_derive. It returns 0 if "key-check"
is set to 0 and the check fails.
=item "key-check" (B<OSSL_KDF_PARAM_FIPS_KEY_CHECK>) <integer>
The default value of 1 causes an error during EVP_KDF_CTX_set_params() if the
length of used key-derivation key (B<OSSL_KDF_PARAM_KEY>) is shorter than 112
bits.
Setting this to zero will ignore the error and set the approved
"fips-indicator" to 0.
This option breaks FIPS compliance if it causes the approved "fips-indicator"
to return 0.
=back
=head1 NOTES
A context for SSKDF can be obtained by calling:
EVP_KDF *kdf = EVP_KDF_fetch(NULL, "SSKDF", NULL);
EVP_KDF_CTX *kctx = EVP_KDF_CTX_new(kdf);
The output length of an SSKDF is specified via the I<keylen>
parameter to the L<EVP_KDF_derive(3)> function.
=head1 EXAMPLES
This example derives 10 bytes using H(x) = SHA-256, with the secret key "secret"
and fixedinfo value "label":
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);
This example derives 10 bytes using H(x) = HMAC(SHA-256), with the secret key "secret",
fixedinfo value "label" and salt "salt":
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(OSSL_KDF_PARAM_SECRET,
"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);
This example derives 10 bytes using H(x) = KMAC128(x,salt,outlen), with the secret key "secret"
fixedinfo value "label", salt of "salt" and KMAC outlen of 20:
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(OSSL_KDF_PARAM_SECRET,
"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);
=head1 CONFORMING TO
NIST SP800-56Cr1.
=head1 SEE ALSO
L<EVP_KDF(3)>,
L<EVP_KDF_CTX_new(3)>,
L<EVP_KDF_CTX_free(3)>,
L<EVP_KDF_CTX_set_params(3)>,
L<EVP_KDF_CTX_get_kdf_size(3)>,
L<EVP_KDF_derive(3)>,
L<EVP_KDF(3)/PARAMETERS>
=head1 HISTORY
This functionality was added in OpenSSL 3.0.
=head1 COPYRIGHT
Copyright 2019-2024 The OpenSSL Project Authors. All Rights Reserved. Copyright
(c) 2019, Oracle and/or its affiliates. All rights reserved.
Licensed under the Apache License 2.0 (the "License"). You may not use
this file except in compliance with the License. You can obtain a copy
in the file LICENSE in the source distribution or at
L<https://www.openssl.org/source/license.html>.
=cut