EVP_KDF-X942-ASN17ssl

The x9.42-2003 asn1 evp_kdf implementation

Overview

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).

The output is considered to be keying material.

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".

The OpenSSL FIPS provider also supports the following parameters:

"fips-indicator" (OSSL_KDF_PARAM_FIPS_APPROVED_INDICATOR) <integer>: A getter that returns 1 if the operation is FIPS approved, or 0 otherwise. This may be used after calling EVP_KDF_derive. It returns 0 if "key-check" parameter is set to 0 and the check fails.

"key-check" (OSSL_KDF_PARAM_FIPS_KEY_CHECK) <integer>: The default value of 1 causes an error during EVP_KDF_CTX_set_params() if the length of used key-derivation key (OSSL_KDF_PARAM_KEY) is shorter than 112 bits. Setting this to zero will ignore the error and set the approved "fips-indicator" to 0. This option breaks FIPS compliance if it causes the approved "fips-indicator" to return 0.

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);

Releases

3 releases since Debian 12 (Bookworm); the text changed 2 times.