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- added random bias to search and tunnel request maximum depth

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- added random (and biased) re-routing of tunnel request to improve tunnel length.


git-svn-id: http://svn.code.sf.net/p/retroshare/code/trunk@4130 b45a01b8-16f6-495d-af2f-9b41ad6348cc
This commit is contained in:
csoler 2011-04-07 20:16:43 +00:00
parent bcdf536c98
commit 8e6962808d
2 changed files with 47 additions and 5 deletions
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46
libretroshare/src/turtle/p3turtle.cc
View File

@ -94,7 +94,8 @@ p3turtle::p3turtle(p3ConnectMgr *cm,ftServer *fs)
_ft_server = fs ;
_ft_controller = fs->getController() ;
srand(time(NULL)) ;
_random_bias = RSRandom::random_u32() ;
addSerialType(new RsTurtleSerialiser());
_last_clean_time = 0 ;
@ -766,7 +767,12 @@ void p3turtle::handleSearchRequest(RsTurtleSearchRequestItem *item)
// If search depth not too large, also forward this search request to all other peers.
//
if(item->depth < TURTLE_MAX_SEARCH_DEPTH)
// We use a random factor on the depth test that is biased by a mix between the session id and the partial tunnel id
// to scramble a possible search-by-depth attack.
//
bool random_bypass = (item->depth == TURTLE_MAX_SEARCH_DEPTH && (_random_bias ^ item->request_id)&0x7==2) ;
if(item->depth < TURTLE_MAX_SEARCH_DEPTH || random_bypass)
{
std::list<std::string> onlineIds ;
mConnMgr->getOnlineList(onlineIds);
@ -1518,11 +1524,38 @@ void p3turtle::handleTunnelRequest(RsTurtleOpenTunnelItem *item)
{
RsStackMutex stack(mTurtleMtx); /********** STACK LOCKED MTX ******/
if(_tunnel_requests_origins.find(item->request_id) != _tunnel_requests_origins.end())
std::map<TurtleTunnelRequestId,TurtleRequestInfo>::iterator it = _tunnel_requests_origins.find(item->request_id) ;
if(it != _tunnel_requests_origins.end())
{
#ifdef P3TURTLE_DEBUG
std::cerr << " This is a bouncing request. Ignoring and deleting item." << std::endl ;
std::cerr << " This is a bouncing request. Ignoring and deleting item." << std::endl ;
#endif
// This trick allows to shorten tunnels, favoring tunnels of smallest length, with a bias that
// depends on a mix between a session-based constant and the tunnel partial id. This means
// that for a given couple of (source,hash), the optimisation always performs the same.
// overall, 80% tunnels are re-routed. The probability of a tunnel to have optimal length is
// thus 0.875^n where n is the length of the tunnel, supposing that it has 2 branching peers
// at each node. This makes:
// n probability
// 1 0.875
// 2 0.76
// 3 0.67
// 4 0.58
// 5 0.512
//
// The lower the probability, the higher the anonymity level.
//
if(it->second.depth > item->depth && ((item->partial_tunnel_id ^ _random_bias)&0x7)>0)
{
//#ifdef P3TURTLE_DEBUG
std::cerr << " re-routing tunnel request. Item age difference = " << time(NULL)-it->second.time_stamp << std::endl;
std::cerr << " - old source: " << it->second.origin << ", old depth=" << it->second.depth << std::endl ;
std::cerr << " - new source: " << item->PeerId() << ", new depth=" << item->depth << std::endl ;
//#endif
it->second.origin = item->PeerId() ;
it->second.depth = item->depth ;
}
return ;
}
// This is a new request. Let's add it to the request map, and forward
@ -1532,6 +1565,7 @@ void p3turtle::handleTunnelRequest(RsTurtleOpenTunnelItem *item)
TurtleRequestInfo& req( _tunnel_requests_origins[item->request_id] ) ;
req.origin = item->PeerId() ;
req.time_stamp = time(NULL) ;
req.depth = item->depth ;
#ifdef TUNNEL_STATISTICS
std::cerr << "storing tunnel request " << (void*)(item->request_id) << std::endl ;
@ -1603,7 +1637,9 @@ void p3turtle::handleTunnelRequest(RsTurtleOpenTunnelItem *item)
// If search depth not too large, also forward this search request to all other peers.
//
if(item->depth < TURTLE_MAX_SEARCH_DEPTH)
bool random_bypass = (item->depth == TURTLE_MAX_SEARCH_DEPTH && (_random_bias ^ item->partial_tunnel_id)&0x7==2) ;
if(item->depth < TURTLE_MAX_SEARCH_DEPTH || random_bypass)
{
std::list<std::string> onlineIds ;
mConnMgr->getOnlineList(onlineIds);

6
libretroshare/src/turtle/p3turtle.h
View File

@ -164,6 +164,7 @@ class TurtleRequestInfo
public:
TurtlePeerId origin ; // where the request came from.
uint32_t time_stamp ; // last time the tunnel was actually used. Used for cleaning old tunnels.
int depth ; // depth of the request. Used to optimize tunnel length.
};
class TurtleTunnel
@ -402,6 +403,11 @@ class p3turtle: public p3Service, /*public pqiMonitor,*/ public RsTurtle,/* publ
/// used to force digging new tunnels
bool _force_digg_new_tunnels ;
/// used as a bias to introduce randomness in a consistent way, for
/// altering tunnel request depths, and tunnel re-routing actions.
///
uint32_t _random_bias ;
#ifdef P3TURTLE_DEBUG
// debug function
void dumpState() ;