1 /*
2 * prng.c
3 *
4 * 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 x917_prng_t x917_prng;
51
52 err_status_t
x917_prng_init(rand_source_func_t random_source)53 x917_prng_init(rand_source_func_t random_source) {
54 uint8_t tmp_key[16];
55 err_status_t status;
56
57 /* initialize output count to zero */
58 x917_prng.octet_count = 0;
59
60 /* set random source */
61 x917_prng.rand = random_source;
62
63 /* initialize secret key from random source */
64 status = random_source(tmp_key, 16);
65 if (status)
66 return status;
67
68 /* expand aes key */
69 aes_expand_encryption_key(tmp_key, 16, &x917_prng.key);
70
71 /* initialize prng state from random source */
72 status = x917_prng.rand((uint8_t *)&x917_prng.state, 16);
73 if (status)
74 return status;
75
76 return err_status_ok;
77 }
78
79 err_status_t
x917_prng_get_octet_string(uint8_t * dest,uint32_t len)80 x917_prng_get_octet_string(uint8_t *dest, uint32_t len) {
81 uint32_t t;
82 v128_t buffer;
83 uint32_t i, tail_len;
84 err_status_t status;
85
86 /*
87 * if we need to re-initialize the prng, do so now
88 *
89 * avoid overflows by subtracting instead of adding
90 */
91 if (x917_prng.octet_count > MAX_PRNG_OUT_LEN - len) {
92 status = x917_prng_init(x917_prng.rand);
93 if (status)
94 return status;
95 }
96 x917_prng.octet_count += len;
97
98 /* find out the time */
99 t = (uint32_t)time(NULL);
100
101 /* loop until we have output enough data */
102 for (i=0; i < len/16; i++) {
103
104 /* exor time into state */
105 x917_prng.state.v32[0] ^= t;
106
107 /* copy state into buffer */
108 v128_copy(&buffer, &x917_prng.state);
109
110 /* apply aes to buffer */
111 aes_encrypt(&buffer, &x917_prng.key);
112
113 /* write data to output */
114 *dest++ = buffer.v8[0];
115 *dest++ = buffer.v8[1];
116 *dest++ = buffer.v8[2];
117 *dest++ = buffer.v8[3];
118 *dest++ = buffer.v8[4];
119 *dest++ = buffer.v8[5];
120 *dest++ = buffer.v8[6];
121 *dest++ = buffer.v8[7];
122 *dest++ = buffer.v8[8];
123 *dest++ = buffer.v8[9];
124 *dest++ = buffer.v8[10];
125 *dest++ = buffer.v8[11];
126 *dest++ = buffer.v8[12];
127 *dest++ = buffer.v8[13];
128 *dest++ = buffer.v8[14];
129 *dest++ = buffer.v8[15];
130
131 /* exor time into buffer */
132 buffer.v32[0] ^= t;
133
134 /* encrypt buffer */
135 aes_encrypt(&buffer, &x917_prng.key);
136
137 /* copy buffer into state */
138 v128_copy(&x917_prng.state, &buffer);
139
140 }
141
142 /* if we need to output any more octets, we'll do so now */
143 tail_len = len % 16;
144 if (tail_len) {
145
146 /* exor time into state */
147 x917_prng.state.v32[0] ^= t;
148
149 /* copy value into buffer */
150 v128_copy(&buffer, &x917_prng.state);
151
152 /* apply aes to buffer */
153 aes_encrypt(&buffer, &x917_prng.key);
154
155 /* write data to output */
156 for (i=0; i < tail_len; i++) {
157 *dest++ = buffer.v8[i];
158 }
159
160 /* now update the state one more time */
161
162 /* exor time into buffer */
163 buffer.v32[0] ^= t;
164
165 /* encrypt buffer */
166 aes_encrypt(&buffer, &x917_prng.key);
167
168 /* copy buffer into state */
169 v128_copy(&x917_prng.state, &buffer);
170
171 }
172
173 return err_status_ok;
174 }
175
176 err_status_t
x917_prng_deinit(void)177 x917_prng_deinit(void) {
178
179 return err_status_ok;
180 }
181