man > EVP_KDF-X942-ASN1(7SSL)

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

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>.

3.0.13                                       2026-07-29                      EVP_KDF-X942-ASN1(7SSL)