1 /* -*- mode: c; c-basic-offset: 4; indent-tabs-mode: nil -*- */
2 /* lib/crypto/krb/checksum_etm.c - checksum for encrypt-then-mac enctypes */
3 /*
4 * Copyright (C) 2015 by the Massachusetts Institute of Technology.
5 * All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 *
11 * * Redistributions of source code must retain the above copyright
12 * notice, this list of conditions and the following disclaimer.
13 *
14 * * Redistributions in binary form must reproduce the above copyright
15 * notice, this list of conditions and the following disclaimer in
16 * the documentation and/or other materials provided with the
17 * distribution.
18 *
19 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
20 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
21 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
22 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
23 * COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
24 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
25 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
26 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
28 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
29 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
30 * OF THE POSSIBILITY OF SUCH DAMAGE.
31 */
32
33 #include "crypto_int.h"
34
35 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)36 krb5int_etm_checksum(const struct krb5_cksumtypes *ctp, krb5_key key,
37 krb5_keyusage usage, const krb5_crypto_iov *data,
38 size_t num_data, krb5_data *output)
39 {
40 krb5_error_code ret;
41 uint8_t label[5];
42 krb5_data label_data = make_data(label, 5), kc = empty_data();
43 krb5_keyblock kb = { 0 };
44
45 /* Derive the checksum key. */
46 store_32_be(usage, label);
47 label[4] = 0x99;
48 label_data = make_data(label, 5);
49 ret = alloc_data(&kc, ctp->hash->hashsize / 2);
50 if (ret)
51 goto cleanup;
52 ret = krb5int_derive_random(ctp->enc, ctp->hash, key, &kc, &label_data,
53 DERIVE_SP800_108_HMAC);
54 if (ret)
55 goto cleanup;
56
57 /* Compute an HMAC with kc over the data. */
58 kb.length = kc.length;
59 kb.contents = (uint8_t *)kc.data;
60 ret = krb5int_hmac_keyblock(ctp->hash, &kb, data, num_data, output);
61
62 cleanup:
63 zapfree(kc.data, kc.length);
64 return ret;
65 }
66