udp now generates a cryptographically secure token for connecting clients. This is later verified.

ot_udp.c

@@ -18,15 +18,40 @@
 #include "trackerlogic.h"
 #include "ot_udp.h"
 #include "ot_stats.h"
+#include "ot_rijndael.h"
 
 static const uint8_t g_static_connid[8] = { 0x23, 0x42, 0x05, 0x17, 0xde, 0x41, 0x50, 0xff };
+static uint32_t g_rijndael_round_key[44] = {0};
+static uint32_t g_key_of_the_hour[2] = {0};
+static ot_time  g_hour_of_the_key;
 
-static void udp_make_connectionid( uint32_t * connid, const ot_ip6 remoteip ) {
-  /* Touch unused variable */
-  (void)remoteip;
+static void udp_generate_rijndael_round_key() {
+  uint8_t key[16];
+  key[0] = random(); key[1] = random(); key[2] = random(); key[3] = random();
+  rijndaelKeySetupEnc128( g_rijndael_round_key, key );
 
-  /* Use a static secret for now */
-  memcpy( connid, g_static_connid, 8 );
+  g_key_of_the_hour[0] = random();
+  g_hour_of_the_key = g_now_minutes;
+}
+
+/* Generate current and previous connection id for ip */
+static void udp_make_connectionid( uint32_t connid[4], const ot_ip6 remoteip ) {
+  uint32_t plain[4], crypt[4];
+  int age, i;
+
+  if( g_now_minutes + 60 > g_hour_of_the_key ) {
+    g_hour_of_the_key = g_now_minutes;
+    g_key_of_the_hour[1] = g_key_of_the_hour[0];
+    g_key_of_the_hour[0] = random();
+  }
+
+  for( age = 0; age < 1; ++age ) {
+    memcpy( plain, remoteip, sizeof( plain ) );
+    for( i=0; i<4; ++i ) plain[i] ^= g_key_of_the_hour[age];
+    rijndaelEncrypt128( g_rijndael_round_key, (uint8_t*)remoteip, (uint8_t*)crypt );
+    connid[2*age  ] = crypt[0] ^ crypt[1];
+    connid[2*age+1] = crypt[2] ^ crypt[3];
+  }
 }
 
 /* UDP implementation according to http://xbtt.sourceforge.net/udp_tracker_protocol.html */
@@ -35,6 +60,7 @@ int handle_udp6( int64 serversocket, struct ot_workstruct *ws ) {
   uint32_t   *inpacket = (uint32_t*)ws->inbuf;
   uint32_t   *outpacket = (uint32_t*)ws->outbuf;
   uint32_t    numwant, left, event, scopeid;
+  uint32_t    connid[4];
   uint16_t    port, remoteport;
   size_t      byte_count, scrape_count;
 
@@ -44,13 +70,29 @@ int handle_udp6( int64 serversocket, struct ot_workstruct *ws ) {
   stats_issue_event( EVENT_ACCEPT, FLAG_UDP, (uintptr_t)remoteip );
   stats_issue_event( EVENT_READ, FLAG_UDP, byte_count );
 
+  /* Minimum udp tracker packet size, also catches error */
+  if( byte_count < 16 )
+    return 1;
+
+  /* Generate the connection id we give out and expect to and from
+     the requesting ip address, this prevents udp spoofing */
+  udp_make_connectionid( connid, remoteip );
+
   /* Initialise hash pointer */
   ws->hash = NULL;
   ws->peer_id = NULL;
 
-  /* Minimum udp tracker packet size, also catches error */
-  if( byte_count < 16 )
+  /* If action is not a ntohl(a) == a == 0, then we
+     expect the derived connection id in first 64 bit */
+  if( inpacket[2] && ( inpacket[0] != connid[0] || inpacket[1] != connid[1] ) &&
+                     ( inpacket[0] != connid[2] || inpacket[1] != connid[3] ) ) {
+    const size_t s = sizeof( "Connection ID missmatch." );
+    outpacket[0] = 3; outpacket[1] = inpacket[3];
+    memcpy( &outpacket[2], "Connection ID missmatch.", s );
+    socket_send6( serversocket, ws->outbuf, 8 + s, remoteip, remoteport, 0 );
+    stats_issue_event( EVENT_CONNID_MISSMATCH, FLAG_UDP, 8 + s );
     return 1;
+  }
 
   switch( ntohl( inpacket[2] ) ) {
     case 0: /* This is a connect action */
@@ -60,7 +102,8 @@ int handle_udp6( int64 serversocket, struct ot_workstruct *ws ) {
 
       outpacket[0] = 0;
       outpacket[1] = inpacket[3];
-      udp_make_connectionid( outpacket + 2, remoteip );
+      outpacket[2] = connid[0];
+      outpacket[3] = connid[1];
 
       socket_send6( serversocket, ws->outbuf, 16, remoteip, remoteport, 0 );
       stats_issue_event( EVENT_CONNECT, FLAG_UDP, 16 );
@@ -146,6 +189,8 @@ static void* udp_worker( void * args ) {
 
 void udp_init( int64 sock, unsigned int worker_count ) {
   pthread_t thread_id;
+  if( !g_rijndael_round_key[0] )
+    udp_generate_rijndael_round_key();
 #ifdef _DEBUG
   fprintf( stderr, " installing %d workers on udp socket %ld", worker_count, (unsigned long)sock );
 #endif