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/* -*- 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;
}
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