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 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. */ 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 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 } 101 102 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 } 130 131 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 } 197 198 void CTR_DRBG_clear(CTR_DRBG_STATE *drbg) { 199 OPENSSL_cleanse(drbg, sizeof(CTR_DRBG_STATE)); 200 } 201