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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'.
=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 Numeric identity
B<EVP_KDF_SS> is the numeric identity for this implementation; it
can be used with the EVP_KDF_CTX_new_id() function.
=head2 Supported controls
The supported controls are:
=over 4
=item B<EVP_KDF_CTRL_SET_MD>
=item B<EVP_KDF_CTRL_SET_MAC>
=item B<EVP_MAC_CTRL_SET_MAC_SIZE>
=item B<EVP_KDF_CTRL_SET_SALT>
These controls work as described in L<EVP_KDF_CTX(3)/CONTROLS>.
=item B<EVP_KDF_CTRL_SET_KEY>
This control expects two arguments: C<unsigned char *secret>, C<size_t secretlen>
The shared secret used for key derivation. This control sets the secret.
EVP_KDF_ctrl_str() takes two type strings for this control:
=over 4
=item "secret"
The value string is used as is.
=item "hexsecret"
The value string is expected to be a hexadecimal number, which will be
decoded before being passed on as the control value.
=back
=item B<EVP_KDF_CTRL_SET_SSKDF_INFO>
This control expects two arguments: C<unsigned char *info>, C<size_t infolen>
An optional value for fixedinfo, also known as otherinfo. This control sets the fixedinfo.
EVP_KDF_ctrl_str() takes two type strings for this control:
=over 4
=item "info"
The value string is used as is.
=item "hexinfo"
The value string is expected to be a hexadecimal number, which will be
decoded before being passed on as the control value.
=back
=back
=head1 NOTES
A context for SSKDF can be obtained by calling:
EVP_KDF_CTX *kctx = EVP_KDF_CTX_new_id(EVP_KDF_SS);
The output length of an SSKDF is specified via the C<keylen>
parameter to the L<EVP_KDF_derive(3)> function.
=head1 EXAMPLE
This example derives 10 bytes using H(x) = SHA-256, with the secret key "secret"
and fixedinfo value "label":
EVP_KDF_CTX *kctx;
unsigned char out[10];
kctx = EVP_KDF_CTX_new_id(EVP_KDF_SS);
if (EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_MD, EVP_sha256()) <= 0) {
error("EVP_KDF_CTRL_SET_MD");
}
if (EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_KEY, "secret", (size_t)6) <= 0) {
error("EVP_KDF_CTRL_SET_KEY");
}
if (EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_SSKDF_INFO, "label", (size_t)5) <= 0) {
error("EVP_KDF_CTRL_SET_SSKDF_INFO");
}
if (EVP_KDF_derive(kctx, out, sizeof(out)) <= 0) {
error("EVP_KDF_derive");
}
EVP_KDF_CTX_free(kctx);
=head1 EXAMPLE
This example derives 10 bytes using H(x) = HMAC(SHA-256), with the secret key "secret",
fixedinfo value "label" and salt "salt":
EVP_KDF_CTX *kctx;
unsigned char out[10];
kctx = EVP_KDF_CTX_new_id(EVP_KDF_SS);
if (EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_MAC, EVP_get_macbyname("HMAC")) <= 0) {
error("EVP_KDF_CTRL_SET_MAC");
}
if (EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_MD, EVP_sha256()) <= 0) {
error("EVP_KDF_CTRL_SET_MD");
}
if (EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_KEY, "secret", (size_t)6) <= 0) {
error("EVP_KDF_CTRL_SET_KEY");
}
if (EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_SSKDF_INFO, "label", (size_t)5) <= 0) {
error("EVP_KDF_CTRL_SET_SSKDF_INFO");
}
if (EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_SALT, "salt", (size_t)4) <= 0) {
error("EVP_KDF_CTRL_SET_SALT");
}
if (EVP_KDF_derive(kctx, out, sizeof(out)) <= 0) {
error("EVP_KDF_derive");
}
EVP_KDF_CTX_free(kctx);
=head1 EXAMPLE
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_CTX *kctx;
unsigned char out[10];
kctx = EVP_KDF_CTX_new_id(EVP_KDF_SS);
if (EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_MAC, EVP_get_macbyname("KMAC128")) <= 0) {
error("EVP_KDF_CTRL_SET_MAC");
}
if (EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_MD, EVP_sha256()) <= 0) {
error("EVP_KDF_CTRL_SET_MD");
}
if (EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_KEY, "secret", (size_t)6) <= 0) {
error("EVP_KDF_CTRL_SET_KEY");
}
if (EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_SSKDF_INFO, "label", (size_t)5) <= 0) {
error("EVP_KDF_CTRL_SET_SSKDF_INFO");
}
/* If not specified the salt will be set to a default value */
if (EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_SALT, "salt", (size_t)4) <= 0) {
error("EVP_KDF_CTRL_SET_SALT");
}
/* If not specified the default size will be the size of the derived key */
if (EVP_KDF_ctrl(kctx, EVP_KDF_CTRL_SET_MAC_SIZE, (size_t)20) <= 0) {
error("EVP_KDF_CTRL_SET_MAC_SIZE");
}
if (EVP_KDF_derive(kctx, out, sizeof(out)) <= 0) {
error("EVP_KDF_derive");
}
EVP_KDF_CTX_free(kctx);
=head1 CONFORMING TO
NIST SP800-56Cr1.
=head1 SEE ALSO
L<EVP_KDF_CTX>,
L<EVP_KDF_CTX_new_id(3)>,
L<EVP_KDF_CTX_free(3)>,
L<EVP_KDF_ctrl(3)>,
L<EVP_KDF_size(3)>,
L<EVP_KDF_derive(3)>,
L<EVP_KDF_CTX(3)/CONTROLS>
=head1 HISTORY
This functionality was added to OpenSSL 3.0.0.
=head1 COPYRIGHT
Copyright 2019 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
|
