397 lines
12 KiB
C
397 lines
12 KiB
C
/*
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* rdbx.c
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*
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* a replay database with extended range, using a rollover counter
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*
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* David A. McGrew
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* Cisco Systems, Inc.
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*/
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/*
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*
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* Copyright (c) 2001-2017, Cisco Systems, Inc.
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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*
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* Redistributions in binary form must reproduce the above
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* copyright notice, this list of conditions and the following
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* disclaimer in the documentation and/or other materials provided
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* with the distribution.
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*
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* Neither the name of the Cisco Systems, Inc. nor the names of its
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* contributors may be used to endorse or promote products derived
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* from this software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
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* INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
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* STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
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* OF THE POSSIBILITY OF SUCH DAMAGE.
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*
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*/
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#ifdef HAVE_CONFIG_H
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#include <config.h>
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#endif
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#include "rdbx.h"
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/*
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* from RFC 3711:
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*
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* A receiver reconstructs the index i of a packet with sequence
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* number SEQ using the estimate
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*
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* i = 2^16 * v + SEQ,
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*
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* where v is chosen from the set { ROC-1, ROC, ROC+1 } such that i is
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* closest to the value 2^16 * ROC + s_l. If the value r+1 is used,
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* then the rollover counter r in the cryptographic context is
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* incremented by one (if the packet containing s is authentic).
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*/
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/*
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* rdbx implementation notes
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*
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* A srtp_xtd_seq_num_t is essentially a sequence number for which some of
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* the data on the wire are implicit. It logically consists of a
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* rollover counter and a sequence number; the sequence number is the
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* explicit part, and the rollover counter is the implicit part.
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*
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* Upon receiving a sequence_number (e.g. in a newly received SRTP
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* packet), the complete srtp_xtd_seq_num_t can be estimated by using a
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* local srtp_xtd_seq_num_t as a basis. This is done using the function
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* srtp_index_guess(&local, &guess, seq_from_packet). This function
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* returns the difference of the guess and the local value. The local
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* srtp_xtd_seq_num_t can be moved forward to the guess using the function
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* srtp_index_advance(&guess, delta), where delta is the difference.
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*
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*
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* A srtp_rdbx_t consists of a srtp_xtd_seq_num_t and a bitmask. The index is highest
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* sequence number that has been received, and the bitmask indicates
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* which of the recent indicies have been received as well. The
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* highest bit in the bitmask corresponds to the index in the bitmask.
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*/
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void srtp_index_init (srtp_xtd_seq_num_t *pi)
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{
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#ifdef NO_64BIT_MATH
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*pi = make64(0, 0);
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#else
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*pi = 0;
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#endif
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}
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void srtp_index_advance (srtp_xtd_seq_num_t *pi, srtp_sequence_number_t s)
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{
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#ifdef NO_64BIT_MATH
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/* a > ~b means a+b will generate a carry */
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/* s is uint16 here */
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*pi = make64(high32(*pi) + (s > ~low32(*pi) ? 1 : 0), low32(*pi) + s);
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#else
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*pi += s;
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#endif
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}
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/*
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* srtp_index_guess(local, guess, s)
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*
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* given a srtp_xtd_seq_num_t local (which represents the last
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* known-to-be-good received srtp_xtd_seq_num_t) and a sequence number s
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* (from a newly arrived packet), sets the contents of *guess to
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* contain the best guess of the packet index to which s corresponds,
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* and returns the difference between *guess and *local
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*
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* nota bene - the output is a signed integer, DON'T cast it to a
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* unsigned integer!
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*/
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int32_t srtp_index_guess (const srtp_xtd_seq_num_t *local, srtp_xtd_seq_num_t *guess, srtp_sequence_number_t s)
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{
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#ifdef NO_64BIT_MATH
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uint32_t local_roc = ((high32(*local) << 16) |
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(low32(*local) >> 16));
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uint16_t local_seq = (uint16_t)(low32(*local));
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#else
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uint32_t local_roc = (uint32_t)(*local >> 16);
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uint16_t local_seq = (uint16_t)*local;
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#endif
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#ifdef NO_64BIT_MATH
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uint32_t guess_roc = ((high32(*guess) << 16) |
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(low32(*guess) >> 16));
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uint16_t guess_seq = (uint16_t)(low32(*guess));
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#else
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uint32_t guess_roc = (uint32_t)(*guess >> 16);
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uint16_t guess_seq = (uint16_t)*guess;
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#endif
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int32_t difference;
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if (local_seq < seq_num_median) {
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if (s - local_seq > seq_num_median) {
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guess_roc = local_roc - 1;
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difference = s - local_seq - seq_num_max;
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} else {
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guess_roc = local_roc;
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difference = s - local_seq;
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}
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} else {
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if (local_seq - seq_num_median > s) {
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guess_roc = local_roc + 1;
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difference = s - local_seq + seq_num_max;
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} else {
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guess_roc = local_roc;
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difference = s - local_seq;
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}
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}
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guess_seq = s;
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/* Note: guess_roc is 32 bits, so this generates a 48-bit result! */
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#ifdef NO_64BIT_MATH
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*guess = make64(guess_roc >> 16,
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(guess_roc << 16) | guess_seq);
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#else
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*guess = (((uint64_t)guess_roc) << 16) | guess_seq;
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#endif
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return difference;
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}
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/*
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* rdbx
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*
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*/
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/*
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* srtp_rdbx_init(&r, ws) initializes the srtp_rdbx_t pointed to by r with window size ws
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*/
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srtp_err_status_t srtp_rdbx_init (srtp_rdbx_t *rdbx, unsigned long ws)
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{
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if (ws == 0) {
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return srtp_err_status_bad_param;
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}
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if (bitvector_alloc(&rdbx->bitmask, ws) != 0) {
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return srtp_err_status_alloc_fail;
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}
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srtp_index_init(&rdbx->index);
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return srtp_err_status_ok;
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}
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/*
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* srtp_rdbx_dealloc(&r) frees memory for the srtp_rdbx_t pointed to by r
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*/
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srtp_err_status_t srtp_rdbx_dealloc (srtp_rdbx_t *rdbx)
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{
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bitvector_dealloc(&rdbx->bitmask);
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return srtp_err_status_ok;
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}
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/*
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* srtp_rdbx_set_roc(rdbx, roc) initalizes the srtp_rdbx_t at the location rdbx
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* to have the rollover counter value roc. If that value is less than
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* the current rollover counter value, then the function returns
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* srtp_err_status_replay_old; otherwise, srtp_err_status_ok is returned.
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*
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*/
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srtp_err_status_t srtp_rdbx_set_roc (srtp_rdbx_t *rdbx, uint32_t roc)
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{
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bitvector_set_to_zero(&rdbx->bitmask);
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#ifdef NO_64BIT_MATH
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#error not yet implemented
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#else
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/* make sure that we're not moving backwards */
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if (roc < (rdbx->index >> 16)) {
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return srtp_err_status_replay_old;
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}
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rdbx->index &= 0xffff; /* retain lowest 16 bits */
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rdbx->index |= ((uint64_t)roc) << 16; /* set ROC */
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#endif
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return srtp_err_status_ok;
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}
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/*
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* srtp_rdbx_get_packet_index(rdbx) returns the value of the packet index
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* for the srtp_rdbx_t pointed to by rdbx
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*
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*/
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srtp_xtd_seq_num_t srtp_rdbx_get_packet_index (const srtp_rdbx_t *rdbx)
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{
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return rdbx->index;
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}
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/*
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* srtp_rdbx_get_window_size(rdbx) returns the value of the window size
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* for the srtp_rdbx_t pointed to by rdbx
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*
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*/
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unsigned long srtp_rdbx_get_window_size (const srtp_rdbx_t *rdbx)
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{
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return bitvector_get_length(&rdbx->bitmask);
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}
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/*
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* srtp_rdbx_check(&r, delta) checks to see if the srtp_xtd_seq_num_t
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* which is at rdbx->index + delta is in the rdb
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*/
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srtp_err_status_t srtp_rdbx_check (const srtp_rdbx_t *rdbx, int delta)
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{
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if (delta > 0) { /* if delta is positive, it's good */
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return srtp_err_status_ok;
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} else if ((int)(bitvector_get_length(&rdbx->bitmask) - 1) + delta < 0) {
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/* if delta is lower than the bitmask, it's bad */
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return srtp_err_status_replay_old;
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} else if (bitvector_get_bit(&rdbx->bitmask,
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(int)(bitvector_get_length(&rdbx->bitmask) - 1) + delta) == 1) {
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/* delta is within the window, so check the bitmask */
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return srtp_err_status_replay_fail;
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}
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/* otherwise, the index is okay */
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return srtp_err_status_ok;
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}
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/*
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* srtp_rdbx_add_index adds the srtp_xtd_seq_num_t at rdbx->window_start + d to
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* replay_db (and does *not* check if that srtp_xtd_seq_num_t appears in db)
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*
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* this function should be called only after replay_check has
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* indicated that the index does not appear in the rdbx, e.g., a mutex
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* should protect the rdbx between these calls if need be
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*/
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srtp_err_status_t srtp_rdbx_add_index (srtp_rdbx_t *rdbx, int delta)
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{
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if (delta > 0) {
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/* shift forward by delta */
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srtp_index_advance(&rdbx->index, delta);
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bitvector_left_shift(&rdbx->bitmask, delta);
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bitvector_set_bit(&rdbx->bitmask, bitvector_get_length(&rdbx->bitmask) - 1);
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} else {
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/* delta is in window */
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bitvector_set_bit(&rdbx->bitmask, bitvector_get_length(&rdbx->bitmask) - 1 + delta);
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}
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/* note that we need not consider the case that delta == 0 */
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return srtp_err_status_ok;
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}
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/*
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* srtp_rdbx_estimate_index(rdbx, guess, s)
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*
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* given an rdbx and a sequence number s (from a newly arrived packet),
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* sets the contents of *guess to contain the best guess of the packet
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* index to which s corresponds, and returns the difference between
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* *guess and the locally stored synch info
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*/
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int32_t srtp_rdbx_estimate_index (const srtp_rdbx_t *rdbx, srtp_xtd_seq_num_t *guess, srtp_sequence_number_t s)
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{
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/*
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* if the sequence number and rollover counter in the rdbx are
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* non-zero, then use the srtp_index_guess(...) function, otherwise, just
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* set the rollover counter to zero (since the srtp_index_guess(...)
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* function might incorrectly guess that the rollover counter is
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* 0xffffffff)
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*/
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#ifdef NO_64BIT_MATH
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/* seq_num_median = 0x8000 */
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if (high32(rdbx->index) > 0 ||
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low32(rdbx->index) > seq_num_median)
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#else
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if (rdbx->index > seq_num_median)
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#endif
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{ return srtp_index_guess(&rdbx->index, guess, s); }
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#ifdef NO_64BIT_MATH
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*guess = make64(0, (uint32_t)s);
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#else
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*guess = s;
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#endif
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#ifdef NO_64BIT_MATH
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return s - (uint16_t)low32(rdbx->index);
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#else
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return s - (uint16_t)rdbx->index;
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#endif
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}
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/*
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* srtp_rdbx_get_roc(rdbx)
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*
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* Get the current rollover counter
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*
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*/
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uint32_t srtp_rdbx_get_roc(const srtp_rdbx_t *rdbx)
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{
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uint32_t roc;
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#ifdef NO_64BIT_MATH
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roc = ((high32(rdbx->index) << 16) | (low32(rdbx->index) >> 16));
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#else
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roc = (uint32_t)(rdbx->index >> 16);
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#endif
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return roc;
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}
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/*
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* srtp_rdbx_set_roc_seq(rdbx, roc, seq) initalizes the srtp_rdbx_t at the
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* location rdbx to have the rollover counter value roc and packet sequence
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* number seq. If the new rollover counter value is less than the current
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* rollover counter value, then the function returns
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* srtp_err_status_replay_old, otherwise, srtp_err_status_ok is returned.
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*/
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srtp_err_status_t srtp_rdbx_set_roc_seq (srtp_rdbx_t *rdbx,
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uint32_t roc,
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uint16_t seq)
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{
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#ifdef NO_64BIT_MATH
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#error not yet implemented
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#else
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/* make sure that we're not moving backwards */
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if (roc < (rdbx->index >> 16)) {
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return srtp_err_status_replay_old;
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}
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rdbx->index = seq;
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rdbx->index |= ((uint64_t)roc) << 16; /* set ROC */
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#endif
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bitvector_set_to_zero(&rdbx->bitmask);
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return srtp_err_status_ok;
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}
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