/* -*- mode: c; c-basic-offset: 4; indent-tabs-mode: nil -*- */

/* lib/crypto/krb/checksum_etm.c - checksum for encrypt-then-mac enctypes */

/*

 * Copyright (C) 2015 by the Massachusetts Institute of Technology.

 * All rights reserved.

 *

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions

 * are met:

 *

 * * Redistributions of source code must retain the above copyright

 *   notice, this list of conditions and the following disclaimer.

 *

 * * Redistributions in binary form must reproduce the above copyright

 *   notice, this list of conditions and the following disclaimer in

 *   the documentation and/or other materials provided with the

 *   distribution.

 *

 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS

 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT

 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS

 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE

 * COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,

 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES

 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR

 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)

 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,

 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)

 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED

 * OF THE POSSIBILITY OF SUCH DAMAGE.

 */

#include "crypto_int.h"

krb5_error_code

krb5int_etm_checksum(const struct krb5_cksumtypes *ctp, krb5_key key,

                     krb5_keyusage usage, const krb5_crypto_iov *data,

                     size_t num_data, krb5_data *output)

{

    krb5_error_code ret;

    uint8_t label[5];

    krb5_data label_data = make_data(label, 5), kc = empty_data();

    krb5_keyblock kb = { 0 };

    /* Derive the checksum key. */

    store_32_be(usage, label);

    label[4] = 0x99;

    label_data = make_data(label, 5);

    ret = alloc_data(&kc, ctp->hash->hashsize / 2);

    if (ret)

        goto cleanup;

    ret = krb5int_derive_random(ctp->enc, ctp->hash, key, &kc, &label_data,

                                DERIVE_SP800_108_HMAC);

    if (ret)

        goto cleanup;

    /* Compute an HMAC with kc over the data. */

    kb.length = kc.length;

    kb.contents = (uint8_t *)kc.data;

    ret = krb5int_hmac_keyblock(ctp->hash, &kb, data, num_data, output);

cleanup:

    zapfree(kc.data, kc.length);

    return ret;

}