man > EVP_KDF-X963(7)

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.

   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.

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 2019-2021 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>.

3.0.13                                       2026-07-29                           EVP_KDF-X963(7SSL)