Alexandre Lision | 8af73cb | 2013-12-10 14:11:20 -0500 | [diff] [blame] | 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 | #define rdbx_high_bit_in_bitmask 127 |
| 49 | |
| 50 | /* |
| 51 | * from draft-ietf-avt-srtp-00.txt: |
| 52 | * |
| 53 | * A receiver reconstructs the index i of a packet with sequence |
| 54 | * number s using the estimate |
| 55 | * |
| 56 | * i = 65,536 * t + s, |
| 57 | * |
| 58 | * where t is chosen from the set { r-1, r, r+1 } such that i is |
| 59 | * closest to the value 65,536 * r + s_l. If the value r+1 is used, |
| 60 | * then the rollover counter r in the cryptographic context is |
| 61 | * incremented by one (if the packet containing s is authentic). |
| 62 | */ |
| 63 | |
| 64 | |
| 65 | |
| 66 | /* |
| 67 | * rdbx implementation notes |
| 68 | * |
| 69 | * A xtd_seq_num_t is essentially a sequence number for which some of |
| 70 | * the data on the wire are implicit. It logically consists of a |
| 71 | * rollover counter and a sequence number; the sequence number is the |
| 72 | * explicit part, and the rollover counter is the implicit part. |
| 73 | * |
| 74 | * Upon receiving a sequence_number (e.g. in a newly received SRTP |
| 75 | * packet), the complete xtd_seq_num_t can be estimated by using a |
| 76 | * local xtd_seq_num_t as a basis. This is done using the function |
| 77 | * index_guess(&local, &guess, seq_from_packet). This function |
| 78 | * returns the difference of the guess and the local value. The local |
| 79 | * xtd_seq_num_t can be moved forward to the guess using the function |
| 80 | * index_advance(&guess, delta), where delta is the difference. |
| 81 | * |
| 82 | * |
| 83 | * A rdbx_t consists of a xtd_seq_num_t and a bitmask. The index is highest |
| 84 | * sequence number that has been received, and the bitmask indicates |
| 85 | * which of the recent indicies have been received as well. The |
| 86 | * highest bit in the bitmask corresponds to the index in the bitmask. |
| 87 | */ |
| 88 | |
| 89 | |
| 90 | void |
| 91 | index_init(xtd_seq_num_t *pi) { |
| 92 | #ifdef NO_64BIT_MATH |
| 93 | *pi = make64(0,0); |
| 94 | #else |
| 95 | *pi = 0; |
| 96 | #endif |
| 97 | } |
| 98 | |
| 99 | void |
| 100 | index_advance(xtd_seq_num_t *pi, sequence_number_t s) { |
| 101 | #ifdef NO_64BIT_MATH |
| 102 | /* a > ~b means a+b will generate a carry */ |
| 103 | /* s is uint16 here */ |
| 104 | *pi = make64(high32(*pi) + (s > ~low32(*pi) ? 1 : 0),low32(*pi) + s); |
| 105 | #else |
| 106 | *pi += s; |
| 107 | #endif |
| 108 | } |
| 109 | |
| 110 | |
| 111 | /* |
| 112 | * index_guess(local, guess, s) |
| 113 | * |
| 114 | * given a xtd_seq_num_t local (which represents the last |
| 115 | * known-to-be-good received xtd_seq_num_t) and a sequence number s |
| 116 | * (from a newly arrived packet), sets the contents of *guess to |
| 117 | * contain the best guess of the packet index to which s corresponds, |
| 118 | * and returns the difference between *guess and *local |
| 119 | * |
| 120 | * nota bene - the output is a signed integer, DON'T cast it to a |
| 121 | * unsigned integer! |
| 122 | */ |
| 123 | |
| 124 | int |
| 125 | index_guess(const xtd_seq_num_t *local, |
| 126 | xtd_seq_num_t *guess, |
| 127 | sequence_number_t s) { |
| 128 | #ifdef NO_64BIT_MATH |
| 129 | uint32_t local_roc = ((high32(*local) << 16) | |
| 130 | (low32(*local) >> 16)); |
| 131 | uint16_t local_seq = (uint16_t) (low32(*local)); |
| 132 | #else |
| 133 | uint32_t local_roc = (uint32_t)(*local >> 16); |
| 134 | uint16_t local_seq = (uint16_t) *local; |
| 135 | #endif |
| 136 | #ifdef NO_64BIT_MATH |
| 137 | uint32_t guess_roc = ((high32(*guess) << 16) | |
| 138 | (low32(*guess) >> 16)); |
| 139 | uint16_t guess_seq = (uint16_t) (low32(*guess)); |
| 140 | #else |
| 141 | uint32_t guess_roc = (uint32_t)(*guess >> 16); |
| 142 | uint16_t guess_seq = (uint16_t) *guess; |
| 143 | #endif |
| 144 | int difference; |
| 145 | |
| 146 | if (local_seq < seq_num_median) { |
| 147 | if (s - local_seq > seq_num_median) { |
| 148 | guess_roc = local_roc - 1; |
| 149 | difference = seq_num_max - s + local_seq; |
| 150 | } else { |
| 151 | guess_roc = local_roc; |
| 152 | difference = s - local_seq; |
| 153 | } |
| 154 | } else { |
| 155 | if (local_seq - seq_num_median > s) { |
| 156 | guess_roc = local_roc+1; |
| 157 | difference = seq_num_max - local_seq + s; |
| 158 | } else { |
| 159 | difference = s - local_seq; |
| 160 | guess_roc = local_roc; |
| 161 | } |
| 162 | } |
| 163 | guess_seq = s; |
| 164 | |
| 165 | /* Note: guess_roc is 32 bits, so this generates a 48-bit result! */ |
| 166 | #ifdef NO_64BIT_MATH |
| 167 | *guess = make64(guess_roc >> 16, |
| 168 | (guess_roc << 16) | guess_seq); |
| 169 | #else |
| 170 | *guess = (((uint64_t) guess_roc) << 16) | guess_seq; |
| 171 | #endif |
| 172 | |
| 173 | return difference; |
| 174 | } |
| 175 | |
| 176 | /* |
| 177 | * rdbx |
| 178 | * |
| 179 | */ |
| 180 | |
| 181 | |
| 182 | /* |
| 183 | * rdbx_init(&r) initalizes the rdbx_t pointed to by r |
| 184 | */ |
| 185 | |
| 186 | err_status_t |
| 187 | rdbx_init(rdbx_t *rdbx) { |
| 188 | v128_set_to_zero(&rdbx->bitmask); |
| 189 | index_init(&rdbx->index); |
| 190 | |
| 191 | return err_status_ok; |
| 192 | } |
| 193 | |
| 194 | |
| 195 | /* |
| 196 | * rdbx_check(&r, delta) checks to see if the xtd_seq_num_t |
| 197 | * which is at rdbx->index + delta is in the rdb |
| 198 | */ |
| 199 | |
| 200 | err_status_t |
| 201 | rdbx_check(const rdbx_t *rdbx, int delta) { |
| 202 | |
| 203 | if (delta > 0) { /* if delta is positive, it's good */ |
| 204 | return err_status_ok; |
| 205 | } else if (rdbx_high_bit_in_bitmask + delta < 0) { |
| 206 | /* if delta is lower than the bitmask, it's bad */ |
| 207 | return err_status_replay_old; |
| 208 | } else if (v128_get_bit(&rdbx->bitmask, |
| 209 | rdbx_high_bit_in_bitmask + delta) == 1) { |
| 210 | /* delta is within the window, so check the bitmask */ |
| 211 | return err_status_replay_fail; |
| 212 | } |
| 213 | /* otherwise, the index is okay */ |
| 214 | |
| 215 | return err_status_ok; |
| 216 | } |
| 217 | |
| 218 | /* |
| 219 | * rdbx_add_index adds the xtd_seq_num_t at rdbx->window_start + d to |
| 220 | * replay_db (and does *not* check if that xtd_seq_num_t appears in db) |
| 221 | * |
| 222 | * this function should be called only after replay_check has |
| 223 | * indicated that the index does not appear in the rdbx, e.g., a mutex |
| 224 | * should protect the rdbx between these calls if need be |
| 225 | */ |
| 226 | |
| 227 | err_status_t |
| 228 | rdbx_add_index(rdbx_t *rdbx, int delta) { |
| 229 | |
| 230 | if (delta > 0) { |
| 231 | /* shift forward by delta */ |
| 232 | index_advance(&rdbx->index, delta); |
| 233 | v128_left_shift(&rdbx->bitmask, delta); |
| 234 | v128_set_bit(&rdbx->bitmask, 127); |
| 235 | } else { |
| 236 | /* delta is in window, so flip bit in bitmask */ |
| 237 | v128_set_bit(&rdbx->bitmask, -delta); |
| 238 | } |
| 239 | |
| 240 | /* note that we need not consider the case that delta == 0 */ |
| 241 | |
| 242 | return err_status_ok; |
| 243 | } |
| 244 | |
| 245 | |
| 246 | |
| 247 | /* |
| 248 | * rdbx_estimate_index(rdbx, guess, s) |
| 249 | * |
| 250 | * given an rdbx and a sequence number s (from a newly arrived packet), |
| 251 | * sets the contents of *guess to contain the best guess of the packet |
| 252 | * index to which s corresponds, and returns the difference between |
| 253 | * *guess and the locally stored synch info |
| 254 | */ |
| 255 | |
| 256 | int |
| 257 | rdbx_estimate_index(const rdbx_t *rdbx, |
| 258 | xtd_seq_num_t *guess, |
| 259 | sequence_number_t s) { |
| 260 | |
| 261 | /* |
| 262 | * if the sequence number and rollover counter in the rdbx are |
| 263 | * non-zero, then use the index_guess(...) function, otherwise, just |
| 264 | * set the rollover counter to zero (since the index_guess(...) |
| 265 | * function might incorrectly guess that the rollover counter is |
| 266 | * 0xffffffff) |
| 267 | */ |
| 268 | |
| 269 | #ifdef NO_64BIT_MATH |
| 270 | /* seq_num_median = 0x8000 */ |
| 271 | if (high32(rdbx->index) > 0 || |
| 272 | low32(rdbx->index) > seq_num_median) |
| 273 | #else |
| 274 | if (rdbx->index > seq_num_median) |
| 275 | #endif |
| 276 | return index_guess(&rdbx->index, guess, s); |
| 277 | |
| 278 | #ifdef NO_64BIT_MATH |
| 279 | *guess = make64(0,(uint32_t) s); |
| 280 | #else |
| 281 | *guess = s; |
| 282 | #endif |
| 283 | |
| 284 | #ifdef NO_64BIT_MATH |
| 285 | return s - (uint16_t) low32(rdbx->index); |
| 286 | #else |
| 287 | return s - (uint16_t) rdbx->index; |
| 288 | #endif |
| 289 | } |