NAME

       EVP_KDF-X942-ASN1 - The X9.42-2003 asn1 EVP_KDF implementation

DESCRIPTION

       The EVP_KDF-X942-ASN1 algorithm implements the key derivation function X942KDF-ASN1. It is
       used by DH KeyAgreement, to derive a key using input such as a shared secret key and other
       info. The other info is DER encoded data that contains a 32 bit counter as well as
       optional fields for "partyu-info", "partyv-info", "supp-pubinfo" and "supp-privinfo".
       This kdf is used by Cryptographic Message Syntax (CMS).

   Identity
       "X942KDF-ASN1" or "X942KDF" 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).

       "secret" (OSSL_KDF_PARAM_SECRET) <octet string>
           The shared secret used for key derivation.  This parameter sets the secret.

       "acvp-info" (OSSL_KDF_PARAM_X942_ACVPINFO) <octet string>
           This value should not be used in production and should only be used for ACVP testing.
           It is an optional octet string containing a combined DER encoded blob of any of the
           optional fields related to "partyu-info", "partyv-info", "supp-pubinfo" and "supp-
           privinfo". If it is specified then none of these other fields should be used.

       "partyu-info" (OSSL_KDF_PARAM_X942_PARTYUINFO) <octet string>
           An optional octet string containing public info contributed by the initiator.

       "ukm" (OSSL_KDF_PARAM_UKM) <octet string>
           An alias for "partyu-info".  In CMS this is the user keying material.

       "partyv-info" (OSSL_KDF_PARAM_X942_PARTYVINFO) <octet string>
           An optional octet string containing public info contributed by the responder.

       "supp-pubinfo" (OSSL_KDF_PARAM_X942_SUPP_PUBINFO) <octet string>
           An optional octet string containing some additional, mutually-known public
           information. Setting this value also sets "use-keybits" to 0.

       "use-keybits" (OSSL_KDF_PARAM_X942_USE_KEYBITS) <integer>
           The default value of 1 will use the KEK key length (in bits) as the "supp-pubinfo". A
           value of 0 disables setting the "supp-pubinfo".

       "supp-privinfo" (OSSL_KDF_PARAM_X942_SUPP_PRIVINFO) <octet string>
           An optional octet string containing some additional, mutually-known private
           information.

       "cekalg" (OSSL_KDF_PARAM_CEK_ALG) <UTF8 string>
           This parameter sets the CEK wrapping algorithm name.  Valid values are "AES-128-WRAP",
           "AES-192-WRAP", "AES-256-WRAP" and "DES3-WRAP".

NOTES

       A context for X942KDF can be obtained by calling:

        EVP_KDF *kdf = EVP_KDF_fetch(NULL, "X942KDF", NULL);
        EVP_KDF_CTX *kctx = EVP_KDF_CTX_new(kdf);

       The output length of an X942KDF is specified via the keylen parameter to the
       EVP_KDF_derive(3) function.

EXAMPLES

       This example derives 24 bytes, with the secret key "secret" and random user keying
       material:

         EVP_KDF_CTX *kctx;
         EVP_KDF_CTX *kctx;
         unsigned char out[192/8];
         unsignred char ukm[64];
         OSSL_PARAM params[5], *p = params;

         if (RAND_bytes(ukm, sizeof(ukm)) <= 0)
             error("RAND_bytes");

         kdf = EVP_KDF_fetch(NULL, "X942KDF", NULL);
         if (kctx == NULL)
             error("EVP_KDF_fetch");
         kctx = EVP_KDF_CTX_new(kdf);
         EVP_KDF_free(kdf);
         if (kctx == NULL)
             error("EVP_KDF_CTX_new");

         *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_DIGEST, "SHA256", 0);
         *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SECRET,
                                                  "secret", (size_t)6);
         *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_UKM, ukm, sizeof(ukm));
         *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_CEK_ALG, "AES-256-WRAP, 0);
         *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

       ANS1 X9.42-2003 RFC 2631

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>.