1 /* Copyright (c) 2017, Google Inc.
2 *
3 * Permission to use, copy, modify, and/or distribute this software for any
4 * purpose with or without fee is hereby granted, provided that the above
5 * copyright notice and this permission notice appear in all copies.
6 *
7 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
8 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
9 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
10 * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
11 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
12 * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
13 * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
14
15 #include <openssl/rand.h>
16
17 #include <openssl/type_check.h>
18 #include <openssl/mem.h>
19
20 #include "internal.h"
21 #include "../cipher/internal.h"
22
23
24 /* Section references in this file refer to SP 800-90Ar1:
25 * http://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-90Ar1.pdf */
26
27 /* See table 3. */
28 static const uint64_t kMaxReseedCount = UINT64_C(1) << 48;
29
CTR_DRBG_init(CTR_DRBG_STATE * drbg,const uint8_t entropy[CTR_DRBG_ENTROPY_LEN],const uint8_t * personalization,size_t personalization_len)30 int CTR_DRBG_init(CTR_DRBG_STATE *drbg,
31 const uint8_t entropy[CTR_DRBG_ENTROPY_LEN],
32 const uint8_t *personalization, size_t personalization_len) {
33 /* Section 10.2.1.3.1 */
34 if (personalization_len > CTR_DRBG_ENTROPY_LEN) {
35 return 0;
36 }
37
38 uint8_t seed_material[CTR_DRBG_ENTROPY_LEN];
39 OPENSSL_memcpy(seed_material, entropy, CTR_DRBG_ENTROPY_LEN);
40
41 for (size_t i = 0; i < personalization_len; i++) {
42 seed_material[i] ^= personalization[i];
43 }
44
45 /* Section 10.2.1.2 */
46
47 /* kInitMask is the result of encrypting blocks with big-endian value 1, 2
48 * and 3 with the all-zero AES-256 key. */
49 static const uint8_t kInitMask[CTR_DRBG_ENTROPY_LEN] = {
50 0x53, 0x0f, 0x8a, 0xfb, 0xc7, 0x45, 0x36, 0xb9, 0xa9, 0x63, 0xb4, 0xf1,
51 0xc4, 0xcb, 0x73, 0x8b, 0xce, 0xa7, 0x40, 0x3d, 0x4d, 0x60, 0x6b, 0x6e,
52 0x07, 0x4e, 0xc5, 0xd3, 0xba, 0xf3, 0x9d, 0x18, 0x72, 0x60, 0x03, 0xca,
53 0x37, 0xa6, 0x2a, 0x74, 0xd1, 0xa2, 0xf5, 0x8e, 0x75, 0x06, 0x35, 0x8e,
54 };
55
56 for (size_t i = 0; i < sizeof(kInitMask); i++) {
57 seed_material[i] ^= kInitMask[i];
58 }
59
60 drbg->ctr = aes_ctr_set_key(&drbg->ks, NULL, &drbg->block, seed_material, 32);
61 OPENSSL_memcpy(drbg->counter.bytes, seed_material + 32, 16);
62 drbg->reseed_counter = 1;
63
64 return 1;
65 }
66
67 OPENSSL_COMPILE_ASSERT(CTR_DRBG_ENTROPY_LEN % AES_BLOCK_SIZE == 0,
68 not_a_multiple_of_block_size);
69
70 /* ctr_inc adds |n| to the last four bytes of |drbg->counter|, treated as a
71 * big-endian number. */
ctr32_add(CTR_DRBG_STATE * drbg,uint32_t n)72 static void ctr32_add(CTR_DRBG_STATE *drbg, uint32_t n) {
73 drbg->counter.words[3] =
74 CRYPTO_bswap4(CRYPTO_bswap4(drbg->counter.words[3]) + n);
75 }
76
CTR_DRBG_update(CTR_DRBG_STATE * drbg,const uint8_t * data,size_t data_len)77 static int CTR_DRBG_update(CTR_DRBG_STATE *drbg, const uint8_t *data,
78 size_t data_len) {
79 /* Section 10.2.1.2. A value of |data_len| which less than
80 * |CTR_DRBG_ENTROPY_LEN| is permitted and acts the same as right-padding
81 * with zeros. This can save a copy. */
82 if (data_len > CTR_DRBG_ENTROPY_LEN) {
83 return 0;
84 }
85
86 uint8_t temp[CTR_DRBG_ENTROPY_LEN];
87 for (size_t i = 0; i < CTR_DRBG_ENTROPY_LEN; i += AES_BLOCK_SIZE) {
88 ctr32_add(drbg, 1);
89 drbg->block(drbg->counter.bytes, temp + i, &drbg->ks);
90 }
91
92 for (size_t i = 0; i < data_len; i++) {
93 temp[i] ^= data[i];
94 }
95
96 drbg->ctr = aes_ctr_set_key(&drbg->ks, NULL, &drbg->block, temp, 32);
97 OPENSSL_memcpy(drbg->counter.bytes, temp + 32, 16);
98
99 return 1;
100 }
101
CTR_DRBG_reseed(CTR_DRBG_STATE * drbg,const uint8_t entropy[CTR_DRBG_ENTROPY_LEN],const uint8_t * additional_data,size_t additional_data_len)102 int CTR_DRBG_reseed(CTR_DRBG_STATE *drbg,
103 const uint8_t entropy[CTR_DRBG_ENTROPY_LEN],
104 const uint8_t *additional_data,
105 size_t additional_data_len) {
106 /* Section 10.2.1.4 */
107 uint8_t entropy_copy[CTR_DRBG_ENTROPY_LEN];
108
109 if (additional_data_len > 0) {
110 if (additional_data_len > CTR_DRBG_ENTROPY_LEN) {
111 return 0;
112 }
113
114 OPENSSL_memcpy(entropy_copy, entropy, CTR_DRBG_ENTROPY_LEN);
115 for (size_t i = 0; i < additional_data_len; i++) {
116 entropy_copy[i] ^= additional_data[i];
117 }
118
119 entropy = entropy_copy;
120 }
121
122 if (!CTR_DRBG_update(drbg, entropy, CTR_DRBG_ENTROPY_LEN)) {
123 return 0;
124 }
125
126 drbg->reseed_counter = 1;
127
128 return 1;
129 }
130
CTR_DRBG_generate(CTR_DRBG_STATE * drbg,uint8_t * out,size_t out_len,const uint8_t * additional_data,size_t additional_data_len)131 int CTR_DRBG_generate(CTR_DRBG_STATE *drbg, uint8_t *out, size_t out_len,
132 const uint8_t *additional_data,
133 size_t additional_data_len) {
134 /* See 9.3.1 */
135 if (out_len > CTR_DRBG_MAX_GENERATE_LENGTH) {
136 return 0;
137 }
138
139 /* See 10.2.1.5.1 */
140 if (drbg->reseed_counter > kMaxReseedCount) {
141 return 0;
142 }
143
144 if (additional_data_len != 0 &&
145 !CTR_DRBG_update(drbg, additional_data, additional_data_len)) {
146 return 0;
147 }
148
149 /* kChunkSize is used to interact better with the cache. Since the AES-CTR
150 * code assumes that it's encrypting rather than just writing keystream, the
151 * buffer has to be zeroed first. Without chunking, large reads would zero
152 * the whole buffer, flushing the L1 cache, and then do another pass (missing
153 * the cache every time) to “encrypt” it. The code can avoid this by
154 * chunking. */
155 static const size_t kChunkSize = 8 * 1024;
156
157 while (out_len >= AES_BLOCK_SIZE) {
158 size_t todo = kChunkSize;
159 if (todo > out_len) {
160 todo = out_len;
161 }
162
163 todo &= ~(AES_BLOCK_SIZE-1);
164 const size_t num_blocks = todo / AES_BLOCK_SIZE;
165
166 if (drbg->ctr) {
167 OPENSSL_memset(out, 0, todo);
168 ctr32_add(drbg, 1);
169 drbg->ctr(out, out, num_blocks, &drbg->ks, drbg->counter.bytes);
170 ctr32_add(drbg, num_blocks - 1);
171 } else {
172 for (size_t i = 0; i < todo; i += AES_BLOCK_SIZE) {
173 ctr32_add(drbg, 1);
174 drbg->block(drbg->counter.bytes, out + i, &drbg->ks);
175 }
176 }
177
178 out += todo;
179 out_len -= todo;
180 }
181
182 if (out_len > 0) {
183 uint8_t block[AES_BLOCK_SIZE];
184 ctr32_add(drbg, 1);
185 drbg->block(drbg->counter.bytes, block, &drbg->ks);
186
187 OPENSSL_memcpy(out, block, out_len);
188 }
189
190 if (!CTR_DRBG_update(drbg, additional_data, additional_data_len)) {
191 return 0;
192 }
193
194 drbg->reseed_counter++;
195 return 1;
196 }
197
CTR_DRBG_clear(CTR_DRBG_STATE * drbg)198 void CTR_DRBG_clear(CTR_DRBG_STATE *drbg) {
199 OPENSSL_cleanse(drbg, sizeof(CTR_DRBG_STATE));
200 }
201