| /* |
| * rdbx.c |
| * |
| * a replay database with extended range, using a rollover counter |
| * |
| * David A. McGrew |
| * Cisco Systems, Inc. |
| */ |
| |
| /* |
| * |
| * Copyright (c) 2001-2017, 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. |
| * |
| */ |
| |
| #ifdef HAVE_CONFIG_H |
| #include <config.h> |
| #endif |
| |
| #include "rdbx.h" |
| |
| /* |
| * from RFC 3711: |
| * |
| * A receiver reconstructs the index i of a packet with sequence |
| * number SEQ using the estimate |
| * |
| * i = 2^16 * v + SEQ, |
| * |
| * where v is chosen from the set { ROC-1, ROC, ROC+1 } such that i is |
| * closest to the value 2^16 * ROC + 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 srtp_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 srtp_xtd_seq_num_t can be estimated by using a |
| * local srtp_xtd_seq_num_t as a basis. This is done using the function |
| * srtp_index_guess(&local, &guess, seq_from_packet). This function |
| * returns the difference of the guess and the local value. The local |
| * srtp_xtd_seq_num_t can be moved forward to the guess using the function |
| * srtp_index_advance(&guess, delta), where delta is the difference. |
| * |
| * |
| * A srtp_rdbx_t consists of a srtp_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 srtp_index_init(srtp_xtd_seq_num_t *pi) |
| { |
| #ifdef NO_64BIT_MATH |
| *pi = make64(0, 0); |
| #else |
| *pi = 0; |
| #endif |
| } |
| |
| void srtp_index_advance(srtp_xtd_seq_num_t *pi, srtp_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 |
| } |
| |
| /* |
| * srtp_index_guess(local, guess, s) |
| * |
| * given a srtp_xtd_seq_num_t local (which represents the last |
| * known-to-be-good received srtp_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! |
| */ |
| |
| int32_t srtp_index_guess(const srtp_xtd_seq_num_t *local, |
| srtp_xtd_seq_num_t *guess, |
| srtp_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 |
| uint32_t guess_roc; |
| uint16_t guess_seq; |
| int32_t difference; |
| |
| if (local_seq < seq_num_median) { |
| if (s - local_seq > seq_num_median) { |
| guess_roc = local_roc - 1; |
| difference = s - local_seq - seq_num_max; |
| } else { |
| guess_roc = local_roc; |
| difference = s - local_seq; |
| } |
| } else { |
| if (local_seq - seq_num_median > s) { |
| guess_roc = local_roc + 1; |
| difference = s - local_seq + seq_num_max; |
| } else { |
| guess_roc = local_roc; |
| difference = s - local_seq; |
| } |
| } |
| 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 |
| * |
| */ |
| |
| /* |
| * srtp_rdbx_init(&r, ws) initializes the srtp_rdbx_t pointed to by r with |
| * window size ws |
| */ |
| srtp_err_status_t srtp_rdbx_init(srtp_rdbx_t *rdbx, unsigned long ws) |
| { |
| if (ws == 0) { |
| return srtp_err_status_bad_param; |
| } |
| |
| if (bitvector_alloc(&rdbx->bitmask, ws) != 0) { |
| return srtp_err_status_alloc_fail; |
| } |
| |
| srtp_index_init(&rdbx->index); |
| |
| return srtp_err_status_ok; |
| } |
| |
| /* |
| * srtp_rdbx_dealloc(&r) frees memory for the srtp_rdbx_t pointed to by r |
| */ |
| srtp_err_status_t srtp_rdbx_dealloc(srtp_rdbx_t *rdbx) |
| { |
| bitvector_dealloc(&rdbx->bitmask); |
| |
| return srtp_err_status_ok; |
| } |
| |
| /* |
| * srtp_rdbx_set_roc(rdbx, roc) initalizes the srtp_rdbx_t at the location rdbx |
| * to have the rollover counter value roc. If that value is less than |
| * the current rollover counter value, then the function returns |
| * srtp_err_status_replay_old; otherwise, srtp_err_status_ok is returned. |
| * |
| */ |
| srtp_err_status_t srtp_rdbx_set_roc(srtp_rdbx_t *rdbx, uint32_t roc) |
| { |
| bitvector_set_to_zero(&rdbx->bitmask); |
| |
| #ifdef NO_64BIT_MATH |
| #error not yet implemented |
| #else |
| |
| /* make sure that we're not moving backwards */ |
| if (roc < (rdbx->index >> 16)) { |
| return srtp_err_status_replay_old; |
| } |
| |
| rdbx->index &= 0xffff; /* retain lowest 16 bits */ |
| rdbx->index |= ((uint64_t)roc) << 16; /* set ROC */ |
| #endif |
| |
| return srtp_err_status_ok; |
| } |
| |
| /* |
| * srtp_rdbx_get_packet_index(rdbx) returns the value of the packet index |
| * for the srtp_rdbx_t pointed to by rdbx |
| * |
| */ |
| srtp_xtd_seq_num_t srtp_rdbx_get_packet_index(const srtp_rdbx_t *rdbx) |
| { |
| return rdbx->index; |
| } |
| |
| /* |
| * srtp_rdbx_get_window_size(rdbx) returns the value of the window size |
| * for the srtp_rdbx_t pointed to by rdbx |
| * |
| */ |
| unsigned long srtp_rdbx_get_window_size(const srtp_rdbx_t *rdbx) |
| { |
| return bitvector_get_length(&rdbx->bitmask); |
| } |
| |
| /* |
| * srtp_rdbx_check(&r, delta) checks to see if the srtp_xtd_seq_num_t |
| * which is at rdbx->index + delta is in the rdb |
| */ |
| srtp_err_status_t srtp_rdbx_check(const srtp_rdbx_t *rdbx, int delta) |
| { |
| if (delta > 0) { /* if delta is positive, it's good */ |
| return srtp_err_status_ok; |
| } else if ((int)(bitvector_get_length(&rdbx->bitmask) - 1) + delta < 0) { |
| /* if delta is lower than the bitmask, it's bad */ |
| return srtp_err_status_replay_old; |
| } else if (bitvector_get_bit( |
| &rdbx->bitmask, |
| (int)(bitvector_get_length(&rdbx->bitmask) - 1) + delta) == |
| 1) { |
| /* delta is within the window, so check the bitmask */ |
| return srtp_err_status_replay_fail; |
| } |
| /* otherwise, the index is okay */ |
| |
| return srtp_err_status_ok; |
| } |
| |
| /* |
| * srtp_rdbx_add_index adds the srtp_xtd_seq_num_t at rdbx->window_start + d to |
| * replay_db (and does *not* check if that srtp_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 |
| */ |
| srtp_err_status_t srtp_rdbx_add_index(srtp_rdbx_t *rdbx, int delta) |
| { |
| if (delta > 0) { |
| /* shift forward by delta */ |
| srtp_index_advance(&rdbx->index, delta); |
| bitvector_left_shift(&rdbx->bitmask, delta); |
| bitvector_set_bit(&rdbx->bitmask, |
| bitvector_get_length(&rdbx->bitmask) - 1); |
| } else { |
| /* delta is in window */ |
| bitvector_set_bit(&rdbx->bitmask, |
| bitvector_get_length(&rdbx->bitmask) - 1 + delta); |
| } |
| |
| /* note that we need not consider the case that delta == 0 */ |
| |
| return srtp_err_status_ok; |
| } |
| |
| /* |
| * srtp_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 |
| */ |
| int32_t srtp_rdbx_estimate_index(const srtp_rdbx_t *rdbx, |
| srtp_xtd_seq_num_t *guess, |
| srtp_sequence_number_t s) |
| { |
| /* |
| * if the sequence number and rollover counter in the rdbx are |
| * non-zero, then use the srtp_index_guess(...) function, otherwise, just |
| * set the rollover counter to zero (since the srtp_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 srtp_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 |
| } |
| |
| /* |
| * srtp_rdbx_get_roc(rdbx) |
| * |
| * Get the current rollover counter |
| * |
| */ |
| uint32_t srtp_rdbx_get_roc(const srtp_rdbx_t *rdbx) |
| { |
| uint32_t roc; |
| |
| #ifdef NO_64BIT_MATH |
| roc = ((high32(rdbx->index) << 16) | (low32(rdbx->index) >> 16)); |
| #else |
| roc = (uint32_t)(rdbx->index >> 16); |
| #endif |
| |
| return roc; |
| } |
| |
| /* |
| * srtp_rdbx_set_roc_seq(rdbx, roc, seq) initalizes the srtp_rdbx_t at the |
| * location rdbx to have the rollover counter value roc and packet sequence |
| * number seq. If the new rollover counter value is less than the current |
| * rollover counter value, then the function returns |
| * srtp_err_status_replay_old, otherwise, srtp_err_status_ok is returned. |
| */ |
| srtp_err_status_t srtp_rdbx_set_roc_seq(srtp_rdbx_t *rdbx, |
| uint32_t roc, |
| uint16_t seq) |
| { |
| #ifdef NO_64BIT_MATH |
| #error not yet implemented |
| #else |
| |
| /* make sure that we're not moving backwards */ |
| if (roc < (rdbx->index >> 16)) { |
| return srtp_err_status_replay_old; |
| } |
| |
| rdbx->index = seq; |
| rdbx->index |= ((uint64_t)roc) << 16; /* set ROC */ |
| #endif |
| |
| bitvector_set_to_zero(&rdbx->bitmask); |
| |
| return srtp_err_status_ok; |
| } |