1 /* 2 * rdbx.c 3 * 4 * a replay database with extended range, using a rollover counter 5 * 6 * David A. McGrew 7 * Cisco Systems, Inc. 8 */ 9 10 /* 11 * 12 * Copyright (c) 2001-2006, Cisco Systems, Inc. 13 * All rights reserved. 14 * 15 * Redistribution and use in source and binary forms, with or without 16 * modification, are permitted provided that the following conditions 17 * are met: 18 * 19 * Redistributions of source code must retain the above copyright 20 * notice, this list of conditions and the following disclaimer. 21 * 22 * Redistributions in binary form must reproduce the above 23 * copyright notice, this list of conditions and the following 24 * disclaimer in the documentation and/or other materials provided 25 * with the distribution. 26 * 27 * Neither the name of the Cisco Systems, Inc. nor the names of its 28 * contributors may be used to endorse or promote products derived 29 * from this software without specific prior written permission. 30 * 31 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 32 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 33 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 34 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 35 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, 36 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES 37 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR 38 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 39 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, 40 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 41 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED 42 * OF THE POSSIBILITY OF SUCH DAMAGE. 43 * 44 */ 45 46 #include "rdbx.h" 47 48 49 /* 50 * from draft-ietf-avt-srtp-00.txt: 51 * 52 * A receiver reconstructs the index i of a packet with sequence 53 * number s using the estimate 54 * 55 * i = 65,536 * t + s, 56 * 57 * where t is chosen from the set { r-1, r, r+1 } such that i is 58 * closest to the value 65,536 * r + s_l. If the value r+1 is used, 59 * then the rollover counter r in the cryptographic context is 60 * incremented by one (if the packet containing s is authentic). 61 */ 62 63 64 65 /* 66 * rdbx implementation notes 67 * 68 * A xtd_seq_num_t is essentially a sequence number for which some of 69 * the data on the wire are implicit. It logically consists of a 70 * rollover counter and a sequence number; the sequence number is the 71 * explicit part, and the rollover counter is the implicit part. 72 * 73 * Upon receiving a sequence_number (e.g. in a newly received SRTP 74 * packet), the complete xtd_seq_num_t can be estimated by using a 75 * local xtd_seq_num_t as a basis. This is done using the function 76 * index_guess(&local, &guess, seq_from_packet). This function 77 * returns the difference of the guess and the local value. The local 78 * xtd_seq_num_t can be moved forward to the guess using the function 79 * index_advance(&guess, delta), where delta is the difference. 80 * 81 * 82 * A rdbx_t consists of a xtd_seq_num_t and a bitmask. The index is highest 83 * sequence number that has been received, and the bitmask indicates 84 * which of the recent indicies have been received as well. The 85 * highest bit in the bitmask corresponds to the index in the bitmask. 86 */ 87 88 89 void 90 index_init(xtd_seq_num_t *pi) { 91 #ifdef NO_64BIT_MATH 92 *pi = make64(0,0); 93 #else 94 *pi = 0; 95 #endif 96 } 97 98 void 99 index_advance(xtd_seq_num_t *pi, sequence_number_t s) { 100 #ifdef NO_64BIT_MATH 101 /* a > ~b means a+b will generate a carry */ 102 /* s is uint16 here */ 103 *pi = make64(high32(*pi) + (s > ~low32(*pi) ? 1 : 0),low32(*pi) + s); 104 #else 105 *pi += s; 106 #endif 107 } 108 109 110 /* 111 * index_guess(local, guess, s) 112 * 113 * given a xtd_seq_num_t local (which represents the last 114 * known-to-be-good received xtd_seq_num_t) and a sequence number s 115 * (from a newly arrived packet), sets the contents of *guess to 116 * contain the best guess of the packet index to which s corresponds, 117 * and returns the difference between *guess and *local 118 * 119 * nota bene - the output is a signed integer, DON'T cast it to a 120 * unsigned integer! 121 */ 122 123 int 124 index_guess(const xtd_seq_num_t *local, 125 xtd_seq_num_t *guess, 126 sequence_number_t s) { 127 #ifdef NO_64BIT_MATH 128 uint32_t local_roc = ((high32(*local) << 16) | 129 (low32(*local) >> 16)); 130 uint16_t local_seq = (uint16_t) (low32(*local)); 131 #else 132 uint32_t local_roc = (uint32_t)(*local >> 16); 133 uint16_t local_seq = (uint16_t) *local; 134 #endif 135 #ifdef NO_64BIT_MATH 136 uint32_t guess_roc = ((high32(*guess) << 16) | 137 (low32(*guess) >> 16)); 138 uint16_t guess_seq = (uint16_t) (low32(*guess)); 139 #else 140 uint32_t guess_roc = (uint32_t)(*guess >> 16); 141 uint16_t guess_seq = (uint16_t) *guess; 142 #endif 143 int difference; 144 145 if (local_seq < seq_num_median) { 146 if (s - local_seq > seq_num_median) { 147 guess_roc = local_roc - 1; 148 // The return value is the relative difference from local_seq to s. 149 // The original value is negation of its purpose. According to document 150 // http://www.ietf.org/rfc/rfc3711.txt, when this condition is true, the 151 // resulting new index should be (local_roc-1, s). But original logic 152 // will end up positive difference and rdbx_check would pass. Hence after 153 // rdbx_add_index would make local index to be the wrong value because 154 // local index should not be updated in this case. For example, when 155 // local index is (1, 100) and next sequence is 65530, the wrong updated 156 // index would be (1, 205). 157 difference = s - local_seq - seq_num_max; 158 } else { 159 guess_roc = local_roc; 160 difference = s - local_seq; 161 } 162 } else { 163 if (local_seq - seq_num_median > s) { 164 guess_roc = local_roc+1; 165 difference = seq_num_max - local_seq + s; 166 } else { 167 difference = s - local_seq; 168 guess_roc = local_roc; 169 } 170 } 171 guess_seq = s; 172 173 /* Note: guess_roc is 32 bits, so this generates a 48-bit result! */ 174 #ifdef NO_64BIT_MATH 175 *guess = make64(guess_roc >> 16, 176 (guess_roc << 16) | guess_seq); 177 #else 178 *guess = (((uint64_t) guess_roc) << 16) | guess_seq; 179 #endif 180 181 return difference; 182 } 183 184 /* 185 * rdbx 186 * 187 */ 188 189 190 /* 191 * rdbx_init(&r, ws) initializes the rdbx_t pointed to by r with window size ws 192 */ 193 194 err_status_t 195 rdbx_init(rdbx_t *rdbx, unsigned long ws) { 196 if (ws == 0) 197 return err_status_bad_param; 198 199 if (bitvector_alloc(&rdbx->bitmask, ws) != 0) 200 return err_status_alloc_fail; 201 202 index_init(&rdbx->index); 203 204 return err_status_ok; 205 } 206 207 /* 208 * rdbx_uninit(&r) uninitializes the rdbx_t pointed to by r 209 */ 210 211 err_status_t 212 rdbx_uninit(rdbx_t *rdbx) { 213 bitvector_dealloc(&rdbx->bitmask); 214 215 return err_status_ok; 216 } 217 218 /* 219 * rdbx_set_roc(rdbx, roc) initalizes the rdbx_t at the location rdbx 220 * to have the rollover counter value roc. If that value is less than 221 * the current rollover counter value, then the function returns 222 * err_status_replay_old; otherwise, err_status_ok is returned. 223 * 224 */ 225 226 err_status_t 227 rdbx_set_roc(rdbx_t *rdbx, uint32_t roc) { 228 bitvector_set_to_zero(&rdbx->bitmask); 229 230 #ifdef NO_64BIT_MATH 231 #error not yet implemented 232 #else 233 234 /* make sure that we're not moving backwards */ 235 if (roc < (rdbx->index >> 16)) 236 return err_status_replay_old; 237 238 rdbx->index &= 0xffff; /* retain lowest 16 bits */ 239 rdbx->index |= ((uint64_t)roc) << 16; /* set ROC */ 240 #endif 241 242 return err_status_ok; 243 } 244 245 /* 246 * rdbx_get_packet_index(rdbx) returns the value of the packet index 247 * for the rdbx_t pointed to by rdbx 248 * 249 */ 250 251 xtd_seq_num_t 252 rdbx_get_packet_index(const rdbx_t *rdbx) { 253 return rdbx->index; 254 } 255 256 /* 257 * rdbx_get_window_size(rdbx) returns the value of the window size 258 * for the rdbx_t pointed to by rdbx 259 * 260 */ 261 262 unsigned long 263 rdbx_get_window_size(const rdbx_t *rdbx) { 264 return bitvector_get_length(&rdbx->bitmask); 265 } 266 267 /* 268 * rdbx_check(&r, delta) checks to see if the xtd_seq_num_t 269 * which is at rdbx->index + delta is in the rdb 270 */ 271 272 err_status_t 273 rdbx_check(const rdbx_t *rdbx, int delta) { 274 275 if (delta > 0) { /* if delta is positive, it's good */ 276 return err_status_ok; 277 } else if ((int)(bitvector_get_length(&rdbx->bitmask) - 1) + delta < 0) { 278 /* if delta is lower than the bitmask, it's bad */ 279 return err_status_replay_old; 280 } else if (bitvector_get_bit(&rdbx->bitmask, 281 (int)(bitvector_get_length(&rdbx->bitmask) - 1) + delta) == 1) { 282 /* delta is within the window, so check the bitmask */ 283 return err_status_replay_fail; 284 } 285 /* otherwise, the index is okay */ 286 287 return err_status_ok; 288 } 289 290 /* 291 * rdbx_add_index adds the xtd_seq_num_t at rdbx->window_start + d to 292 * replay_db (and does *not* check if that xtd_seq_num_t appears in db) 293 * 294 * this function should be called only after replay_check has 295 * indicated that the index does not appear in the rdbx, e.g., a mutex 296 * should protect the rdbx between these calls if need be 297 */ 298 299 err_status_t 300 rdbx_add_index(rdbx_t *rdbx, int delta) { 301 302 if (delta > 0) { 303 /* shift forward by delta */ 304 index_advance(&rdbx->index, delta); 305 bitvector_left_shift(&rdbx->bitmask, delta); 306 bitvector_set_bit(&rdbx->bitmask, bitvector_get_length(&rdbx->bitmask) - 1); 307 } else { 308 /* delta is in window, so flip bit in bitmask */ 309 bitvector_set_bit(&rdbx->bitmask, -delta); 310 } 311 312 /* note that we need not consider the case that delta == 0 */ 313 314 return err_status_ok; 315 } 316 317 318 319 /* 320 * rdbx_estimate_index(rdbx, guess, s) 321 * 322 * given an rdbx and a sequence number s (from a newly arrived packet), 323 * sets the contents of *guess to contain the best guess of the packet 324 * index to which s corresponds, and returns the difference between 325 * *guess and the locally stored synch info 326 */ 327 328 int 329 rdbx_estimate_index(const rdbx_t *rdbx, 330 xtd_seq_num_t *guess, 331 sequence_number_t s) { 332 333 /* 334 * if the sequence number and rollover counter in the rdbx are 335 * non-zero, then use the index_guess(...) function, otherwise, just 336 * set the rollover counter to zero (since the index_guess(...) 337 * function might incorrectly guess that the rollover counter is 338 * 0xffffffff) 339 */ 340 341 #ifdef NO_64BIT_MATH 342 /* seq_num_median = 0x8000 */ 343 if (high32(rdbx->index) > 0 || 344 low32(rdbx->index) > seq_num_median) 345 #else 346 if (rdbx->index > seq_num_median) 347 #endif 348 return index_guess(&rdbx->index, guess, s); 349 350 #ifdef NO_64BIT_MATH 351 *guess = make64(0,(uint32_t) s); 352 #else 353 *guess = s; 354 #endif 355 356 #ifdef NO_64BIT_MATH 357 return s - (uint16_t) low32(rdbx->index); 358 #else 359 return s - (uint16_t) rdbx->index; 360 #endif 361 } 362
