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
50 ctr_prng_t ctr_prng;
51
52 err_status_t
ctr_prng_init(rand_source_func_t random_source)53 ctr_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);
70 if (status)
71 return status;
72
73 return err_status_ok;
74 }
75
76 err_status_t
ctr_prng_get_octet_string(void * dest,uint32_t len)77 ctr_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
102 err_status_t
ctr_prng_deinit(void)103 ctr_prng_deinit(void) {
104
105 /* nothing */
106
107 return err_status_ok;
108 }
109