| /* |
| * rdbx.c |
| * |
| * a replay database with extended range, using a rollover counter |
| * |
| * David A. McGrew |
| * Cisco Systems, Inc. |
| */ |
| |
| /* |
| * |
| * Copyright (c) 2001-2006, Cisco Systems, Inc. |
| * All rights reserved. |
| * |
| * Redistribution and use in source and binary forms, with or without |
| * modification, are permitted provided that the following conditions |
| * are met: |
| * |
| * Redistributions of source code must retain the above copyright |
| * notice, this list of conditions and the following disclaimer. |
| * |
| * Redistributions in binary form must reproduce the above |
| * copyright notice, this list of conditions and the following |
| * disclaimer in the documentation and/or other materials provided |
| * with the distribution. |
| * |
| * Neither the name of the Cisco Systems, Inc. nor the names of its |
| * contributors may be used to endorse or promote products derived |
| * from this software without specific prior written permission. |
| * |
| * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |
| * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT |
| * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS |
| * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE |
| * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, |
| * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES |
| * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR |
| * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) |
| * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, |
| * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) |
| * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED |
| * OF THE POSSIBILITY OF SUCH DAMAGE. |
| * |
| */ |
| |
| #include "rdbx.h" |
| |
| #define rdbx_high_bit_in_bitmask 127 |
| |
| /* |
| * from draft-ietf-avt-srtp-00.txt: |
| * |
| * A receiver reconstructs the index i of a packet with sequence |
| * number s using the estimate |
| * |
| * i = 65,536 * t + s, |
| * |
| * where t is chosen from the set { r-1, r, r+1 } such that i is |
| * closest to the value 65,536 * r + s_l. If the value r+1 is used, |
| * then the rollover counter r in the cryptographic context is |
| * incremented by one (if the packet containing s is authentic). |
| */ |
| |
| |
| |
| /* |
| * rdbx implementation notes |
| * |
| * A xtd_seq_num_t is essentially a sequence number for which some of |
| * the data on the wire are implicit. It logically consists of a |
| * rollover counter and a sequence number; the sequence number is the |
| * explicit part, and the rollover counter is the implicit part. |
| * |
| * Upon receiving a sequence_number (e.g. in a newly received SRTP |
| * packet), the complete xtd_seq_num_t can be estimated by using a |
| * local xtd_seq_num_t as a basis. This is done using the function |
| * index_guess(&local, &guess, seq_from_packet). This function |
| * returns the difference of the guess and the local value. The local |
| * xtd_seq_num_t can be moved forward to the guess using the function |
| * index_advance(&guess, delta), where delta is the difference. |
| * |
| * |
| * A rdbx_t consists of a xtd_seq_num_t and a bitmask. The index is highest |
| * sequence number that has been received, and the bitmask indicates |
| * which of the recent indicies have been received as well. The |
| * highest bit in the bitmask corresponds to the index in the bitmask. |
| */ |
| |
| |
| void |
| index_init(xtd_seq_num_t *pi) { |
| #ifdef NO_64BIT_MATH |
| *pi = make64(0,0); |
| #else |
| *pi = 0; |
| #endif |
| } |
| |
| void |
| index_advance(xtd_seq_num_t *pi, sequence_number_t s) { |
| #ifdef NO_64BIT_MATH |
| /* a > ~b means a+b will generate a carry */ |
| /* s is uint16 here */ |
| *pi = make64(high32(*pi) + (s > ~low32(*pi) ? 1 : 0),low32(*pi) + s); |
| #else |
| *pi += s; |
| #endif |
| } |
| |
| |
| /* |
| * index_guess(local, guess, s) |
| * |
| * given a xtd_seq_num_t local (which represents the last |
| * known-to-be-good received xtd_seq_num_t) and a sequence number s |
| * (from a newly arrived packet), sets the contents of *guess to |
| * contain the best guess of the packet index to which s corresponds, |
| * and returns the difference between *guess and *local |
| * |
| * nota bene - the output is a signed integer, DON'T cast it to a |
| * unsigned integer! |
| */ |
| |
| int |
| index_guess(const xtd_seq_num_t *local, |
| xtd_seq_num_t *guess, |
| sequence_number_t s) { |
| #ifdef NO_64BIT_MATH |
| uint32_t local_roc = ((high32(*local) << 16) | |
| (low32(*local) >> 16)); |
| uint16_t local_seq = (uint16_t) (low32(*local)); |
| #else |
| uint32_t local_roc = (uint32_t)(*local >> 16); |
| uint16_t local_seq = (uint16_t) *local; |
| #endif |
| #ifdef NO_64BIT_MATH |
| uint32_t guess_roc = ((high32(*guess) << 16) | |
| (low32(*guess) >> 16)); |
| uint16_t guess_seq = (uint16_t) (low32(*guess)); |
| #else |
| uint32_t guess_roc = (uint32_t)(*guess >> 16); |
| uint16_t guess_seq = (uint16_t) *guess; |
| #endif |
| int difference; |
| |
| if (local_seq < seq_num_median) { |
| if (s - local_seq > seq_num_median) { |
| guess_roc = local_roc - 1; |
| difference = seq_num_max - s + local_seq; |
| } else { |
| guess_roc = local_roc; |
| difference = s - local_seq; |
| } |
| } else { |
| if (local_seq - seq_num_median > s) { |
| guess_roc = local_roc+1; |
| difference = seq_num_max - local_seq + s; |
| } else { |
| difference = s - local_seq; |
| guess_roc = local_roc; |
| } |
| } |
| guess_seq = s; |
| |
| /* Note: guess_roc is 32 bits, so this generates a 48-bit result! */ |
| #ifdef NO_64BIT_MATH |
| *guess = make64(guess_roc >> 16, |
| (guess_roc << 16) | guess_seq); |
| #else |
| *guess = (((uint64_t) guess_roc) << 16) | guess_seq; |
| #endif |
| |
| return difference; |
| } |
| |
| /* |
| * rdbx |
| * |
| */ |
| |
| |
| /* |
| * rdbx_init(&r) initalizes the rdbx_t pointed to by r |
| */ |
| |
| err_status_t |
| rdbx_init(rdbx_t *rdbx) { |
| v128_set_to_zero(&rdbx->bitmask); |
| index_init(&rdbx->index); |
| |
| return err_status_ok; |
| } |
| |
| |
| /* |
| * rdbx_check(&r, delta) checks to see if the xtd_seq_num_t |
| * which is at rdbx->index + delta is in the rdb |
| */ |
| |
| err_status_t |
| rdbx_check(const rdbx_t *rdbx, int delta) { |
| |
| if (delta > 0) { /* if delta is positive, it's good */ |
| return err_status_ok; |
| } else if (rdbx_high_bit_in_bitmask + delta < 0) { |
| /* if delta is lower than the bitmask, it's bad */ |
| return err_status_replay_old; |
| } else if (v128_get_bit(&rdbx->bitmask, |
| rdbx_high_bit_in_bitmask + delta) == 1) { |
| /* delta is within the window, so check the bitmask */ |
| return err_status_replay_fail; |
| } |
| /* otherwise, the index is okay */ |
| |
| return err_status_ok; |
| } |
| |
| /* |
| * rdbx_add_index adds the xtd_seq_num_t at rdbx->window_start + d to |
| * replay_db (and does *not* check if that xtd_seq_num_t appears in db) |
| * |
| * this function should be called only after replay_check has |
| * indicated that the index does not appear in the rdbx, e.g., a mutex |
| * should protect the rdbx between these calls if need be |
| */ |
| |
| err_status_t |
| rdbx_add_index(rdbx_t *rdbx, int delta) { |
| |
| if (delta > 0) { |
| /* shift forward by delta */ |
| index_advance(&rdbx->index, delta); |
| v128_left_shift(&rdbx->bitmask, delta); |
| v128_set_bit(&rdbx->bitmask, 127); |
| } else { |
| /* delta is in window, so flip bit in bitmask */ |
| v128_set_bit(&rdbx->bitmask, -delta); |
| } |
| |
| /* note that we need not consider the case that delta == 0 */ |
| |
| return err_status_ok; |
| } |
| |
| |
| |
| /* |
| * rdbx_estimate_index(rdbx, guess, s) |
| * |
| * given an rdbx and a sequence number s (from a newly arrived packet), |
| * sets the contents of *guess to contain the best guess of the packet |
| * index to which s corresponds, and returns the difference between |
| * *guess and the locally stored synch info |
| */ |
| |
| int |
| rdbx_estimate_index(const rdbx_t *rdbx, |
| xtd_seq_num_t *guess, |
| sequence_number_t s) { |
| |
| /* |
| * if the sequence number and rollover counter in the rdbx are |
| * non-zero, then use the index_guess(...) function, otherwise, just |
| * set the rollover counter to zero (since the index_guess(...) |
| * function might incorrectly guess that the rollover counter is |
| * 0xffffffff) |
| */ |
| |
| #ifdef NO_64BIT_MATH |
| /* seq_num_median = 0x8000 */ |
| if (high32(rdbx->index) > 0 || |
| low32(rdbx->index) > seq_num_median) |
| #else |
| if (rdbx->index > seq_num_median) |
| #endif |
| return index_guess(&rdbx->index, guess, s); |
| |
| #ifdef NO_64BIT_MATH |
| *guess = make64(0,(uint32_t) s); |
| #else |
| *guess = s; |
| #endif |
| |
| #ifdef NO_64BIT_MATH |
| return s - (uint16_t) low32(rdbx->index); |
| #else |
| return s - (uint16_t) rdbx->index; |
| #endif |
| } |