/* * 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 #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 #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 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; }