NAME

EVP_KDF-X942 - The X9.42-2001 asn1 EVP_KDF implementation

DESCRIPTION

The EVP_KDF-X942 algorithm implements the key derivation function (X942KDF). X942KDF is used by Cryptographic Message Syntax (CMS) for 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.

Identity

"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 "key" (OSSL_KDF_PARAM_KEY) <octet string>; The shared secret used for key derivation. This parameter sets the secret.
"ukm" (OSSL_KDF_PARAM_UKM) <octet string>: This parameter is an optional random string that is provided by the sender called "partyAInfo". In CMS this is the user keying material.
"cekalg" (OSSL_KDF_PARAM_CEK_ALG) <UTF8 string>: This parameter sets the CEK wrapping algorithm name.

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 EXAMPLES

This example derives 24 bytes, with the secret key "secret" and a 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);
 if (kctx == NULL)
     error("EVP_KDF_CTX_new");
 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_UKM, ukm, sizeof(ukm));
 *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_CEK_ALG,
                                         SN_id_smime_alg_CMS3DESwrap,
                                         strlen(SN_id_smime_alg_CMS3DESwrap));
 *p = OSSL_PARAM_construct_end();
 if (EVP_KDF_CTX_set_params(kctx, params) <= 0)
     error("EVP_KDF_CTX_set_params");
 if (EVP_KDF_derive(kctx, out, sizeof(out)) <= 0)
     error("EVP_KDF_derive");

 EVP_KDF_CTX_free(kctx);

CONFORMING TO

RFC 2631

COPYRIGHT

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.