Updated: 2022/Sep/29

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EVP_KDF-X963(7)                     OpenSSL                    EVP_KDF-X963(7)



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>.



3.0.12                            2023-05-07                   EVP_KDF-X963(7)