Add chaff to outgoing instructions (closes #26 github issue)

src/network/transportfragment.cc

@@ -144,6 +144,7 @@ vector<Fragment> Fragmenter::make_fragments( const Instruction &inst, int MTU )
        || (inst.new_num() != last_instruction.new_num())
        || (inst.ack_num() != last_instruction.ack_num())
        || (inst.throwaway_num() != last_instruction.throwaway_num())
+       || (inst.chaff() != last_instruction.chaff())
        || (inst.protocol_version() != last_instruction.protocol_version())
        || (last_MTU != MTU) ) {
     next_instruction_id++;

src/network/transportsender.cc

@@ -21,6 +21,8 @@
 #include <algorithm>
 #include <list>
 #include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
 
 #include "transportsender.h"
 #include "transportfragment.h"
@@ -46,6 +48,7 @@ TransportSender<MyState>::TransportSender( Connection *s_connection, MyState &in
     SEND_MINDELAY( 15 ),
     last_heard( 0 )
 {
+  srand( time( NULL ) ); /* for chaff */
 }
 
 /* Try to send roughly two frames per RTT, bounded by limits on frame rate */
@@ -257,6 +260,18 @@ void TransportSender<MyState>::rationalize_states( void )
   }
 }
 
+static const string make_chaff( void )
+{
+  const int CHAFF_MAX = 16;
+
+  char chaff[ CHAFF_MAX ];
+  for ( int i = 0; i < CHAFF_MAX; i++ ) {
+    chaff[ i ] = rand() % 256;
+  }
+  int chaff_len = rand() % (CHAFF_MAX + 1);
+  return string( chaff, chaff_len );
+}
+
 template <class MyState>
 void TransportSender<MyState>::send_in_fragments( string diff, uint64_t new_num )
 {
@@ -268,6 +283,7 @@ void TransportSender<MyState>::send_in_fragments( string diff, uint64_t new_num
   inst.set_ack_num( ack_num );
   inst.set_throwaway_num( sent_states.front().num );
   inst.set_diff( diff );
+  inst.set_chaff( make_chaff() );
 
   if ( new_num == uint64_t(-1) ) {
     shutdown_tries++;

src/protobufs/transportinstruction.proto

@@ -11,4 +11,6 @@ message Instruction {
   optional uint64 throwaway_num = 5;
 
   optional bytes diff = 6;
+
+  optional bytes chaff = 7;
 }