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      1 /*
      2  * rdb.c
      3  *
      4  * Implements a replay database for packet security
      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 
     47 #include "rdb.h"
     48 
     49 
     50 /*
     51  * this implementation of a replay database works as follows:
     52  *
     53  * window_start is the index of the first packet in the window
     54  * bitmask      a bit-buffer, containing the most recently entered
     55  *              index as the leftmost bit
     56  *
     57  */
     58 
     59 /* rdb_init initalizes rdb */
     60 
     61 err_status_t
     62 rdb_init(rdb_t *rdb) {
     63   v128_set_to_zero(&rdb->bitmask);
     64   rdb->window_start = 0;
     65   return err_status_ok;
     66 }
     67 
     68 /*
     69  * rdb_check checks to see if index appears in rdb
     70  */
     71 
     72 err_status_t
     73 rdb_check(const rdb_t *rdb, uint32_t index) {
     74 
     75   /* if the index appears after (or at very end of) the window, its good */
     76   if (index >= rdb->window_start + rdb_bits_in_bitmask)
     77     return err_status_ok;
     78 
     79   /* if the index appears before the window, its bad */
     80   if (index < rdb->window_start)
     81     return err_status_replay_old;
     82 
     83   /* otherwise, the index appears within the window, so check the bitmask */
     84   if (v128_get_bit(&rdb->bitmask, (index - rdb->window_start)) == 1)
     85     return err_status_replay_fail;
     86 
     87   /* otherwise, the index is okay */
     88   return err_status_ok;
     89 }
     90 
     91 /*
     92  * rdb_add_index adds index to rdb_t (and does *not* check if
     93  * index appears in db)
     94  *
     95  * this function should be called only after rdb_check has
     96  * indicated that the index does not appear in the rdb, e.g., a mutex
     97  * should protect the rdb between these calls
     98  */
     99 
    100 err_status_t
    101 rdb_add_index(rdb_t *rdb, uint32_t index) {
    102   int delta;
    103 
    104   /* here we *assume* that index > rdb->window_start */
    105 
    106   delta = (index - rdb->window_start);
    107   if (delta < rdb_bits_in_bitmask) {
    108 
    109     /* if the index is within the window, set the appropriate bit */
    110     v128_set_bit(&rdb->bitmask, delta);
    111 
    112   } else {
    113 
    114     delta -= rdb_bits_in_bitmask - 1;
    115 
    116     /* shift the window forward by delta bits*/
    117     v128_left_shift(&rdb->bitmask, delta);
    118     v128_set_bit(&rdb->bitmask, rdb_bits_in_bitmask - 1);
    119     rdb->window_start += delta;
    120 
    121   }
    122 
    123   return err_status_ok;
    124 }
    125 
    126 err_status_t
    127 rdb_increment(rdb_t *rdb) {
    128 
    129   if (rdb->window_start++ > 0x7fffffff)
    130     return err_status_key_expired;
    131   return err_status_ok;
    132 }
    133 
    134 uint32_t
    135 rdb_get_value(const rdb_t *rdb) {
    136   return rdb->window_start;
    137 }
    138