1/*
2 * ctr_prng.c
3 *
4 * counter mode based pseudorandom source
5 *
6 * David A. McGrew
7 * Cisco Systems, Inc.
8 */
9/*
10 *
11 * Copyright(c) 2001-2006 Cisco Systems, Inc.
12 * All rights reserved.
13 *
14 * Redistribution and use in source and binary forms, with or without
15 * modification, are permitted provided that the following conditions
16 * are met:
17 *
18 *   Redistributions of source code must retain the above copyright
19 *   notice, this list of conditions and the following disclaimer.
20 *
21 *   Redistributions in binary form must reproduce the above
22 *   copyright notice, this list of conditions and the following
23 *   disclaimer in the documentation and/or other materials provided
24 *   with the distribution.
25 *
26 *   Neither the name of the Cisco Systems, Inc. nor the names of its
27 *   contributors may be used to endorse or promote products derived
28 *   from this software without specific prior written permission.
29 *
30 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
31 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
32 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
33 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
34 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
35 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
36 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
37 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
38 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
39 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
40 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
41 * OF THE POSSIBILITY OF SUCH DAMAGE.
42 *
43 */
44
45
46#include "prng.h"
47
48/* single, global prng structure */
49
50ctr_prng_t ctr_prng;
51
52err_status_t
53ctr_prng_init(rand_source_func_t random_source) {
54  uint8_t tmp_key[32];
55  err_status_t status;
56
57  /* initialize output count to zero */
58  ctr_prng.octet_count = 0;
59
60  /* set random source */
61  ctr_prng.rand = random_source;
62
63  /* initialize secret key from random source */
64  status = random_source(tmp_key, 32);
65  if (status)
66    return status;
67
68  /* initialize aes ctr context with random key */
69  status = aes_icm_context_init(&ctr_prng.state, tmp_key, 30);
70  if (status)
71    return status;
72
73  return err_status_ok;
74}
75
76err_status_t
77ctr_prng_get_octet_string(void *dest, uint32_t len) {
78  err_status_t status;
79
80  /*
81   * if we need to re-initialize the prng, do so now
82   *
83   * avoid 32-bit overflows by subtracting instead of adding
84   */
85  if (ctr_prng.octet_count > MAX_PRNG_OUT_LEN - len) {
86    status = ctr_prng_init(ctr_prng.rand);
87    if (status)
88      return status;
89  }
90  ctr_prng.octet_count += len;
91
92  /*
93   * write prng output
94   */
95  status = aes_icm_output(&ctr_prng.state, (uint8_t*)dest, len);
96  if (status)
97    return status;
98
99  return err_status_ok;
100}
101
102err_status_t
103ctr_prng_deinit(void) {
104
105  /* nothing */
106
107  return err_status_ok;
108}
109