Add Brandon Black's replay window code to SPTPS.

diff --git a/src/sptps.c b/src/sptps.c
index 12c6c7f..b907dad 100644 (file)
--- a/src/sptps.c
+++ b/src/sptps.c
@@ -1,6 +1,7 @@
 /*
     sptps.c -- Simple Peer-to-Peer Security
-    Copyright (C) 2011 Guus Sliepen <guus@tinc-vpn.org>,
+    Copyright (C) 2011-2012 Guus Sliepen <guus@tinc-vpn.org>,
+                  2010      Brandon L. Black <blblack@gmail.com>
 
     This program is free software; you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
@@ -27,6 +28,8 @@
 #include "prf.h"
 #include "sptps.h"
 
+unsigned int sptps_replaywin = 16;
+
 /*
    Nonce MUST be exchanged first (done)
    Signatures MUST be done over both nonces, to guarantee the signature is fresh
@@ -415,15 +418,42 @@ static bool sptps_receive_data_datagram(sptps_t *s, const char *data, size_t len
                return receive_handshake(s, data + 5, len - 5);
        }
 
-       if(seqno < s->inseqno) {
-               fprintf(stderr, "Received late or replayed packet: %d < %d\n", seqno, s->inseqno);
-               return true;
+       // Replay protection using a sliding window of configurable size.
+       // s->inseqno is expected sequence number
+       // seqno is received sequence number
+       // s->late[] is a circular buffer, a 1 bit means a packet has not been received yet
+       // The circular buffer contains bits for sequence numbers from s->inseqno - s->replaywin * 8 to (but excluding) s->inseqno.
+       if(s->replaywin) {
+               if(seqno != s->inseqno) {
+                       if(seqno >= s->inseqno + s->replaywin * 8) {
+                               // Prevent packets that jump far ahead of the queue from causing many others to be dropped.
+                               if(s->farfuture++ < s->replaywin >> 2) {
+                                       fprintf(stderr, "Packet is %d seqs in the future, dropped (%u)\n", seqno - s->inseqno, s->farfuture);
+                                       return false;
+                               }
+                               // Unless we have seen lots of them, in which case we consider the others lost.
+                               fprintf(stderr, "Lost %d packets\n", seqno - s->inseqno);
+                               memset(s->late, 0, s->replaywin);
+                       } else if (seqno < s->inseqno) {
+                               // If the sequence number is farther in the past than the bitmap goes, or if the packet was already received, drop it.
+                               if((s->inseqno >= s->replaywin * 8 && seqno < s->inseqno - s->replaywin * 8) || !(s->late[(seqno / 8) % s->replaywin] & (1 << seqno % 8))) {
+                                       fprintf(stderr, "Received late or replayed packet, seqno %d, last received %d", seqno, s->inseqno);
+                                       return false;
+                               }
+                       } else {
+                               // We missed some packets. Mark them in the bitmap as being late.
+                               for(int i = s->inseqno; i < seqno; i++)
+                                       s->late[(i / 8) % s->replaywin] |= 1 << i % 8;
+                       }
+               }
+
+               // Mark the current packet as not being late.
+               s->late[(seqno / 8) % s->replaywin] &= ~(1 << seqno % 8);
+               s->farfuture = 0;
        }
 
        if(seqno > s->inseqno)
-               fprintf(stderr, "Missed %d packets\n", seqno - s->inseqno);
-
-       s->inseqno = seqno + 1;
+               s->inseqno = seqno + 1;
 
        uint16_t netlen = htons(len - 21);
 
@@ -461,6 +491,7 @@ static bool sptps_receive_data_datagram(sptps_t *s, const char *data, size_t len
 
        return true;
 }
+
 // Receive incoming data. Check if it contains a complete record, if so, handle it.
 bool sptps_receive_data(sptps_t *s, const char *data, size_t len) {
        if(s->datagram)
@@ -564,6 +595,12 @@ bool sptps_start(sptps_t *s, void *handle, bool initiator, bool datagram, ecdsa_
        s->datagram = datagram;
        s->mykey = mykey;
        s->hiskey = hiskey;
+       s->replaywin = sptps_replaywin;
+       if(s->replaywin) {
+               s->late = malloc(s->replaywin);
+               if(!s->late)
+                       return error(s, errno, strerror(errno));
+       }
 
        s->label = malloc(labellen);
        if(!s->label)
@@ -602,5 +639,7 @@ bool sptps_stop(sptps_t *s) {
        s->key = NULL;
        free(s->label);
        s->label = NULL;
+       free(s->late);
+       s->late = NULL;
        return true;
 }

diff --git a/src/sptps.h b/src/sptps.h
index 0616ac7..5037c46 100644 (file)
--- a/src/sptps.h
+++ b/src/sptps.h
@@ -56,6 +56,9 @@ typedef struct sptps {
        cipher_t incipher;
        digest_t indigest;
        uint32_t inseqno;
+       unsigned int replaywin;
+       unsigned int farfuture;
+       char *late;
 
        bool outstate;
        cipher_t outcipher;
@@ -77,6 +80,7 @@ typedef struct sptps {
        receive_record_t receive_record;
 } sptps_t;
 
+extern unsigned int sptps_replaywin;
 extern bool sptps_start(sptps_t *s, void *handle, bool initiator, bool datagram, ecdsa_t mykey, ecdsa_t hiskey, const char *label, size_t labellen, send_data_t send_data, receive_record_t receive_record);
 extern bool sptps_stop(sptps_t *s);
 extern bool sptps_send_record(sptps_t *s, uint8_t type, const char *data, uint16_t len);