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EVP_KDF-X942-ASN1(7)                OpenSSL               EVP_KDF-X942-ASN1(7)



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 in OpenSSL 3.0.

COPYRIGHT
       Copyright 2019-2022 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-X942-ASN1(7)