EVP_KDF-KB(7)

NAME
EVP_KDF-KB - The Key-Based EVP_KDF implementation

DESCRIPTION
The EVP_KDF-KB algorithm implements the Key-Based key derivation function (KBKDF). KBKDF derives a key from repeated application of a keyed MAC to an input secret (and other optional values).

  Identity
"KBKDF" 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>
"mode" (OSSL_KDF_PARAM_MODE) <UTF8 string>
"mac" (OSSL_KDF_PARAM_MAC) <UTF8 string>
"digest" (OSSL_KDF_PARAM_DIGEST) <UTF8 string>
"cipher" (OSSL_KDF_PARAM_DIGEST) <UTF8 string>
"key" (OSSL_KDF_PARAM_KEY) <octet string>
"salt" (OSSL_KDF_PARAM_SALT) <octet string>
"info (OSSL_KDF_PARAM_INFO) <octet string>
"seed" (OSSL_KDF_PARAM_SEED) <octet string>

The mode parameter determines which flavor of KBKDF to use - currently the choices are "counter" and "feedback". Counter is the default, and will be used if unspecified. The seed parameter is unused in counter mode.

The parameters key, salt, info, and seed correspond to KI, Label, Context, and IV (respectively) in SP800-108. As in that document, salt, info, and seed are optional and may be omitted.

Depending on whether mac is CMAC or HMAC, either digest or cipher is required (respectively) and the other is unused.

NOTES
A context for KBKDF can be obtained by calling:

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

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

Note that currently OpenSSL only implements counter and feedback modes. Other variants may be supported in the future.

EXAMPLES
This example derives 10 bytes using COUNTER-HMAC-SHA256, with KI "secret", Label "label", and Context "context".

 EVP_KDF *kdf;
 EVP_KDF_CTX *kctx;
 unsigned char out[10];
 OSSL_PARAM params[6], *p = params;

 kdf = EVP_KDF_fetch(NULL, "KBKDF", NULL);
 kctx = EVP_KDF_CTX_new(kdf);
 EVP_KDF_free(kdf);

 *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_DIGEST,
                                         "SHA2-256", 0);
 *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_MAC,
                                         "HMAC", 0);
 *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_KEY,
                                          "secret", strlen("secret"))
 *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SALT,
                                          "label", strlen("label"));
 *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_INFO,
                                          "context", strlen("context"));
 *p = OSSL_PARAM_construct_end();
 if (EVP_KDF_CTX_set_params(kctx, params) <= 0)
     error("EVP_KDF_CTX_set_params");
 else if (EVP_KDF_derive(kctx, out, sizeof(out)) <= 0)
     error("EVP_KDF_derive");

 EVP_KDF_CTX_free(kctx);

This example derives 10 bytes using FEEDBACK-CMAC-AES256, with KI "secret", Label "label", and IV "sixteen bytes iv".

 EVP_KDF *kdf;
 EVP_KDF_CTX *kctx;
 unsigned char out[10];
 OSSL_PARAM params[8], *p = params;
 unsigned char *iv = "sixteen bytes iv";

 kdf = EVP_KDF_fetch(NULL, "KBKDF", NULL);
 kctx = EVP_KDF_CTX_new(kdf);
 EVP_KDF_free(kdf);

 *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_CIPHER, "AES256", 0);
 *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_MAC, "CMAC", 0);
 *p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_MODE, "FEEDBACK", 0);
 *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_KEY,
                                          "secret", strlen("secret"));
 *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SALT,
                                          "label", strlen("label"));
 *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_INFO,
                                          "context", strlen("context"));
 *p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SEED,
                                          iv, strlen(iv));
 *p = OSSL_PARAM_construct_end();
 if (EVP_KDF_CTX_set_params(kctx, params) <= 0)
     error("EVP_KDF_CTX_set_params");
 else if (EVP_KDF_derive(kctx, out, sizeof(out)) <= 0)
     error("EVP_KDF_derive");

 EVP_KDF_CTX_free(kctx);

CONFORMING TO
NIST SP800-108, IETF RFC 6803, IETF RFC 8009.

SEE ALSO
EVP_KDF(3), EVP_KDF_CTX_free(3), EVP_KDF_size(3), EVP_KDF_derive(3), "PARAMETERS" in EVP_KDF(3)

HISTORY
This functionality was added to OpenSSL 3.0.

COPYRIGHT
Copyright 2019 The OpenSSL Project Authors. All Rights Reserved. Copyright 2019 Red Hat, Inc.

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>.