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 to 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>.