EVP_KDF-KB(7SSL) OpenSSL EVP_KDF-KB(7SSL)
NAME
EVP_KDF-KB - The Key-Based EVP_KDF implementation
DESCRIPTION
The EVP_KDF-KB algorithm implements the Key-Based key derivation
function (KBKDF). KBKDF derives a key from repeated application of a
keyed MAC to an input secret (and other optional values).
The output is considered to be keying material.
Identity
"KBKDF" is the name for this implementation; it can be used with the
EVP_KDF_fetch() function.
Supported parameters
The supported parameters are:
"mode" (OSSL_KDF_PARAM_MODE) <UTF8 string>
The mode parameter determines which flavor of KBKDF to use -
currently the choices are "counter" and "feedback". "counter" is the
default, and will be used if unspecified.
"mac" (OSSL_KDF_PARAM_MAC) <UTF8 string>
The value is either CMAC, HMAC, KMAC128 or KMAC256.
"digest" (OSSL_KDF_PARAM_DIGEST) <UTF8 string>
"cipher" (OSSL_KDF_PARAM_CIPHER) <UTF8 string>
"properties" (OSSL_KDF_PARAM_PROPERTIES) <UTF8 string>
"key" (OSSL_KDF_PARAM_KEY) <octet string>
"salt" (OSSL_KDF_PARAM_SALT) <octet string>
"info (OSSL_KDF_PARAM_INFO) <octet string>
"seed" (OSSL_KDF_PARAM_SEED) <octet string>
The seed parameter is unused in counter mode.
"use-l" (OSSL_KDF_PARAM_KBKDF_USE_L) <integer>
Set to 0 to disable use of the optional Fixed Input data 'L' (see
SP800-108). The default value of 1 will be used if unspecified.
"use-separator" (OSSL_KDF_PARAM_KBKDF_USE_SEPARATOR) <integer>
Set to 0 to disable use of the optional Fixed Input data 'zero
separator' (see SP800-108) that is placed between the Label and
Context. The default value of 1 will be used if unspecified.
"r" (OSSL_KDF_PARAM_KBKDF_R) <integer>
Set the fixed value 'r', indicating the length of the counter in
bits.
Supported values are 8, 16, 24, and 32. The default value of 32
will be used if unspecified.
The OpenSSL FIPS provider also supports the following parameters:
"fips-indicator" (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.
"key-check" (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
(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.
Depending on whether mac is CMAC or HMAC, either digest or cipher is
required (respectively) and the other is unused. They are unused for
KMAC128 and KMAC256.
The parameters key, salt, info, and seed correspond to KI, Label,
Context, and IV (respectively) in SP800-108. As in that document, salt,
info, and seed are optional and may be omitted.
"mac", "digest", cipher" and "properties" are described in "PARAMETERS"
in EVP_KDF(3).
NOTES
A context for KBKDF can be obtained by calling:
EVP_KDF *kdf = EVP_KDF_fetch(NULL, "KBKDF", NULL);
EVP_KDF_CTX *kctx = EVP_KDF_CTX_new(kdf);
The output length of an KBKDF is specified via the "keylen" parameter to
the EVP_KDF_derive(3) function.
Note that currently OpenSSL only implements counter and feedback modes.
Other variants may be supported in the future.
EXAMPLES
This example derives 10 bytes using COUNTER-HMAC-SHA256, with KI
"secret", Label "label", and Context "context".
EVP_KDF *kdf;
EVP_KDF_CTX *kctx;
unsigned char out[10];
OSSL_PARAM params[6], *p = params;
kdf = EVP_KDF_fetch(NULL, "KBKDF", NULL);
kctx = EVP_KDF_CTX_new(kdf);
EVP_KDF_free(kdf);
*p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_DIGEST,
"SHA2-256", 0);
*p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_MAC,
"HMAC", 0);
*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_KEY,
"secret", strlen("secret"));
*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SALT,
"label", strlen("label"));
*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_INFO,
"context", strlen("context"));
*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 FEEDBACK-CMAC-AES256, with KI
"secret", Label "label", and IV "sixteen bytes iv".
EVP_KDF *kdf;
EVP_KDF_CTX *kctx;
unsigned char out[10];
OSSL_PARAM params[8], *p = params;
unsigned char *iv = "sixteen bytes iv";
kdf = EVP_KDF_fetch(NULL, "KBKDF", NULL);
kctx = EVP_KDF_CTX_new(kdf);
EVP_KDF_free(kdf);
*p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_CIPHER, "AES256", 0);
*p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_MAC, "CMAC", 0);
*p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_MODE, "FEEDBACK", 0);
*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_KEY,
"secret", strlen("secret"));
*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SALT,
"label", strlen("label"));
*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_INFO,
"context", strlen("context"));
*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SEED,
iv, strlen(iv));
*p = OSSL_PARAM_construct_end();
if (EVP_KDF_derive(kctx, out, sizeof(out), params) <= 0)
error("EVP_KDF_derive");
EVP_KDF_CTX_free(kctx);
CONFORMING TO
NIST SP800-108, IETF RFC 6803, IETF RFC 8009.
SEE ALSO
EVP_KDF(3), EVP_KDF_CTX_free(3), EVP_KDF_CTX_get_kdf_size(3),
EVP_KDF_derive(3), "PARAMETERS" in EVP_KDF(3)
HISTORY
This functionality was added in OpenSSL 3.0.
Support for KMAC was added in OpenSSL 3.1.
COPYRIGHT
Copyright 2019-2024 The OpenSSL Project Authors. All Rights Reserved.
Copyright 2019 Red Hat, Inc.
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
<https://www.openssl.org/source/license.html>.
3.5.4 2025-09-30 EVP_KDF-KB(7SSL)
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