EVP_KDF-X963(7SSL) OpenSSL EVP_KDF-X963(7SSL)
NAME
EVP_KDF-X963 - The X9.63-2001 EVP_KDF implementation
DESCRIPTION
The EVP_KDF-X963 algorithm implements the key derivation function
(X963KDF). X963KDF is used by Cryptographic Message Syntax (CMS) for EC
KeyAgreement, to derive a key using input such as a shared secret key
and shared info.
The output is considered to be keying material.
Identity
"X963KDF" is the name for this implementation; it can be used with the
EVP_KDF_fetch() function.
Supported parameters
The supported parameters are:
"properties" (OSSL_KDF_PARAM_PROPERTIES) <UTF8 string>
"digest" (OSSL_KDF_PARAM_DIGEST) <UTF8 string>
These parameters work as described in "PARAMETERS" in EVP_KDF(3).
"key" (OSSL_KDF_PARAM_KEY) <octet string>
The shared secret used for key derivation. This parameter sets the
secret.
"info" (OSSL_KDF_PARAM_INFO) <octet string>
This parameter specifies an optional value for shared info.
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 any "***-check" related parameter is set to 0 and the
check fails.
"digest-check" (OSSL_KDF_PARAM_FIPS_DIGEST_CHECK) <int>
The default value of 1 causes an error during
EVP_KDF_CTX_set_params() if used digest is not approved. 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.
According to ANSI X9.63-2001, the following are approved digest
algorithms: SHA2-224, SHA2-256, SHA2-384, SHA2-512, SHA2-512/224,
SHA2-512/256, SHA3-224, SHA3-256, SHA3-384, SHA3-512.
"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.
NOTES
X963KDF is very similar to the SSKDF that uses a digest as the auxiliary
function, X963KDF appends the counter to the secret, whereas SSKDF
prepends the counter.
A context for X963KDF can be obtained by calling:
EVP_KDF *kdf = EVP_KDF_fetch(NULL, "X963KDF", NULL);
EVP_KDF_CTX *kctx = EVP_KDF_CTX_new(kdf);
The output length of an X963KDF is specified via the keylen parameter to
the EVP_KDF_derive(3) function.
EXAMPLES
This example derives 10 bytes, with the secret key "secret" and
sharedinfo value "label":
EVP_KDF *kdf;
EVP_KDF_CTX *kctx;
unsigned char out[10];
OSSL_PARAM params[4], *p = params;
kdf = EVP_KDF_fetch(NULL, "X963KDF", 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_SECRET,
"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);
CONFORMING TO
"SEC 1: Elliptic Curve Cryptography"
SEE ALSO
EVP_KDF(3), EVP_KDF_CTX_new(3), EVP_KDF_CTX_free(3),
EVP_KDF_CTX_set_params(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.
COPYRIGHT
Copyright 2019-2024 The OpenSSL Project Authors. 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
<https://www.openssl.org/source/license.html>.
3.5.4 2025-09-30 EVP_KDF-X963(7SSL)
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