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:

       "mode" (OSSL_KDF_PARAM_MODE) <UTF8 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.

       "mac" (OSSL_KDF_PARAM_MAC) <UTF8 string>
           The value is either CMAC or HMAC.

       "digest" (OSSL_KDF_PARAM_DIGEST) <UTF8 string>
       "cipher" (OSSL_KDF_PARAM_CIPHER) <UTF8 string>
       "properties" (OSSL_KDF_PARAM_PROPERTIES) <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 seed parameter is unused in counter mode.

       "use-l" (OSSL_KDF_PARAM_KBKDF_USE_L) <integer>
           Set to 0 to disable use of the optional Fixed Input data 'L' (see SP800-108).  The default value of 1
           will be used if unspecified.

       "use-separator" (OSSL_KDF_PARAM_KBKDF_USE_SEPARATOR) <integer>
           Set to 0 to disable use of the optional Fixed Input data 'zero separator'  (see  SP800-108)  that  is
           placed between the Label and Context.  The default value of 1 will be used if unspecified.

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

       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.

       "mac", "digest", cipher" and "properties" are described in "PARAMETERS" in EVP_KDF(3).

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_derive(kctx, out, sizeof(out), params) <= 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_derive(kctx, out, sizeof(out), params) <= 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_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 2019-2021 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>.

3.0.13                                             2025-02-05                                   EVP_KDF-KB(7SSL)