privacy: Stream isolation for Tor

According to Tor's extensions to the SOCKS protocol
(https://gitweb.torproject.org/torspec.git/tree/socks-extensions.txt)
it is possible to perform stream isolation by providing authentication
to the proxy. Each set of credentials will create a new circuit,
which makes it harder to correlate connections.

This patch adds an option, `-proxyrandomize` (on by default) that randomizes
credentials for every outgoing connection, thus creating a new circuit.

    2015-03-16 15:29:59 SOCKS5 Sending proxy authentication 3842137544:3256031132

1 files changed, 7 insertions, 6 deletions

diff --git a/src/init.cpp b/src/init.cpp
index 4d9c233c8c..8f52d254f4 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -301,6 +301,7 @@ std::string HelpMessage(HelpMessageMode mode)
     strUsage += HelpMessageOpt("-permitbaremultisig", strprintf(_("Relay non-P2SH multisig (default: %u)"), 1));
     strUsage += HelpMessageOpt("-port=<port>", strprintf(_("Listen for connections on <port> (default: %u or testnet: %u)"), 8333, 18333));
     strUsage += HelpMessageOpt("-proxy=<ip:port>", _("Connect through SOCKS5 proxy"));
+    strUsage += HelpMessageOpt("-proxyrandomize", strprintf(_("Randomize credentials for every proxy connection. This enables Tor stream isolation (default: %u)"), 1));
     strUsage += HelpMessageOpt("-seednode=<ip>", _("Connect to a node to retrieve peer addresses, and disconnect"));
     strUsage += HelpMessageOpt("-timeout=<n>", strprintf(_("Specify connection timeout in milliseconds (minimum: 1, default: %d)"), DEFAULT_CONNECT_TIMEOUT));
 #ifdef USE_UPNP
@@ -351,7 +352,7 @@ std::string HelpMessage(HelpMessageMode mode)
         strUsage += HelpMessageOpt("-flushwallet", strprintf(_("Run a thread to flush wallet periodically (default: %u)"), 1));
         strUsage += HelpMessageOpt("-stopafterblockimport", strprintf(_("Stop running after importing blocks from disk (default: %u)"), 0));
     }
-    string debugCategories = "addrman, alert, bench, coindb, db, lock, rand, rpc, selectcoins, mempool, net"; // Don't translate these and qt below
+    string debugCategories = "addrman, alert, bench, coindb, db, lock, rand, rpc, selectcoins, mempool, net, proxy"; // Don't translate these and qt below
     if (mode == HMM_BITCOIN_QT)
         debugCategories += ", qt";
     strUsage += HelpMessageOpt("-debug=<category>", strprintf(_("Output debugging information (default: %u, supplying <category> is optional)"), 0) + ". " +
@@ -891,10 +892,10 @@ bool AppInit2(boost::thread_group& threadGroup)
         }
     }
 
-    CService addrProxy;
+    proxyType addrProxy;
     bool fProxy = false;
     if (mapArgs.count("-proxy")) {
-        addrProxy = CService(mapArgs["-proxy"], 9050);
+        addrProxy = proxyType(CService(mapArgs["-proxy"], 9050), GetArg("-proxyrandomize", true));
         if (!addrProxy.IsValid())
             return InitError(strprintf(_("Invalid -proxy address: '%s'"), mapArgs["-proxy"]));
 
@@ -904,14 +905,14 @@ bool AppInit2(boost::thread_group& threadGroup)
         fProxy = true;
     }
 
-    // -onion can override normal proxy, -noonion disables tor entirely
+    // -onion can override normal proxy, -noonion disables connecting to .onion entirely
     if (!(mapArgs.count("-onion") && mapArgs["-onion"] == "0") &&
         (fProxy || mapArgs.count("-onion"))) {
-        CService addrOnion;
+        proxyType addrOnion;
         if (!mapArgs.count("-onion"))
             addrOnion = addrProxy;
         else
-            addrOnion = CService(mapArgs["-onion"], 9050);
+            addrOnion = proxyType(CService(mapArgs["-onion"], 9050), GetArg("-proxyrandomize", true));
         if (!addrOnion.IsValid())
             return InitError(strprintf(_("Invalid -onion address: '%s'"), mapArgs["-onion"]));
         SetProxy(NET_TOR, addrOnion);