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 to 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>.