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

6 files changed, 129 insertions, 79 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);
diff --git a/src/netbase.cpp b/src/netbase.cpp
index a2ac6575bc..1837cfa9c3 100644
--- a/src/netbase.cpp
+++ b/src/netbase.cpp
@@ -12,6 +12,7 @@
 #include "hash.h"
 #include "sync.h"
 #include "uint256.h"
+#include "random.h"
 #include "util.h"
 #include "utilstrencodings.h"
 
@@ -38,7 +39,7 @@ using namespace std;
 
 // Settings
 static proxyType proxyInfo[NET_MAX];
-static CService nameProxy;
+static proxyType nameProxy;
 static CCriticalSection cs_proxyInfos;
 int nConnectTimeout = DEFAULT_CONNECT_TIMEOUT;
 bool fNameLookup = false;
@@ -285,59 +286,100 @@ bool static InterruptibleRecv(char* data, size_t len, int timeout, SOCKET& hSock
     return len == 0;
 }
 
-bool static Socks5(string strDest, int port, SOCKET& hSocket)
+struct ProxyCredentials
+{
+    std::string username;
+    std::string password;
+};
+
+/** Connect using SOCKS5 (as described in RFC1928) */
+bool static Socks5(string strDest, int port, const ProxyCredentials *auth, SOCKET& hSocket)
 {
     LogPrintf("SOCKS5 connecting %s\n", strDest);
-    if (strDest.size() > 255)
-    {
+    if (strDest.size() > 255) {
         CloseSocket(hSocket);
         return error("Hostname too long");
     }
-    char pszSocks5Init[] = "\5\1\0";
-    ssize_t nSize = sizeof(pszSocks5Init) - 1;
-
-    ssize_t ret = send(hSocket, pszSocks5Init, nSize, MSG_NOSIGNAL);
-    if (ret != nSize)
-    {
+    // Accepted authentication methods
+    std::vector<uint8_t> vSocks5Init;
+    vSocks5Init.push_back(0x05);
+    if (auth) {
+        vSocks5Init.push_back(0x02); // # METHODS
+        vSocks5Init.push_back(0x00); // X'00' NO AUTHENTICATION REQUIRED
+        vSocks5Init.push_back(0x02); // X'02' USERNAME/PASSWORD (RFC1929)
+    } else {
+        vSocks5Init.push_back(0x01); // # METHODS
+        vSocks5Init.push_back(0x00); // X'00' NO AUTHENTICATION REQUIRED
+    }
+    ssize_t ret = send(hSocket, (const char*)begin_ptr(vSocks5Init), vSocks5Init.size(), MSG_NOSIGNAL);
+    if (ret != (ssize_t)vSocks5Init.size()) {
         CloseSocket(hSocket);
         return error("Error sending to proxy");
     }
     char pchRet1[2];
-    if (!InterruptibleRecv(pchRet1, 2, SOCKS5_RECV_TIMEOUT, hSocket))
-    {
+    if (!InterruptibleRecv(pchRet1, 2, SOCKS5_RECV_TIMEOUT, hSocket)) {
         CloseSocket(hSocket);
         return error("Error reading proxy response");
     }
-    if (pchRet1[0] != 0x05 || pchRet1[1] != 0x00)
-    {
+    if (pchRet1[0] != 0x05) {
         CloseSocket(hSocket);
         return error("Proxy failed to initialize");
     }
-    string strSocks5("\5\1");
-    strSocks5 += '\000'; strSocks5 += '\003';
-    strSocks5 += static_cast<char>(std::min((int)strDest.size(), 255));
-    strSocks5 += strDest;
-    strSocks5 += static_cast<char>((port >> 8) & 0xFF);
-    strSocks5 += static_cast<char>((port >> 0) & 0xFF);
-    ret = send(hSocket, strSocks5.data(), strSocks5.size(), MSG_NOSIGNAL);
-    if (ret != (ssize_t)strSocks5.size())
-    {
+    if (pchRet1[1] == 0x02 && auth) {
+        // Perform username/password authentication (as described in RFC1929)
+        std::vector<uint8_t> vAuth;
+        vAuth.push_back(0x01);
+        if (auth->username.size() > 255 || auth->password.size() > 255)
+            return error("Proxy username or password too long");
+        vAuth.push_back(auth->username.size());
+        vAuth.insert(vAuth.end(), auth->username.begin(), auth->username.end());
+        vAuth.push_back(auth->password.size());
+        vAuth.insert(vAuth.end(), auth->password.begin(), auth->password.end());
+        ret = send(hSocket, (const char*)begin_ptr(vAuth), vAuth.size(), MSG_NOSIGNAL);
+        if (ret != (ssize_t)vAuth.size()) {
+            CloseSocket(hSocket);
+            return error("Error sending authentication to proxy");
+        }
+        LogPrint("proxy", "SOCKS5 sending proxy authentication %s:%s\n", auth->username, auth->password);
+        char pchRetA[2];
+        if (!InterruptibleRecv(pchRetA, 2, SOCKS5_RECV_TIMEOUT, hSocket)) {
+            CloseSocket(hSocket);
+            return error("Error reading proxy authentication response");
+        }
+        if (pchRetA[0] != 0x01 || pchRetA[1] != 0x00) {
+            CloseSocket(hSocket);
+            return error("Proxy authentication unsuccesful");
+        }
+    } else if (pchRet1[1] == 0x00) {
+        // Perform no authentication
+    } else {
+        CloseSocket(hSocket);
+        return error("Proxy requested wrong authentication method %02x", pchRet1[1]);
+    }
+    std::vector<uint8_t> vSocks5;
+    vSocks5.push_back(0x05); // VER protocol version
+    vSocks5.push_back(0x01); // CMD CONNECT
+    vSocks5.push_back(0x00); // RSV Reserved
+    vSocks5.push_back(0x03); // ATYP DOMAINNAME
+    vSocks5.push_back(strDest.size()); // Length<=255 is checked at beginning of function
+    vSocks5.insert(vSocks5.end(), strDest.begin(), strDest.end());
+    vSocks5.push_back((port >> 8) & 0xFF);
+    vSocks5.push_back((port >> 0) & 0xFF);
+    ret = send(hSocket, (const char*)begin_ptr(vSocks5), vSocks5.size(), MSG_NOSIGNAL);
+    if (ret != (ssize_t)vSocks5.size()) {
         CloseSocket(hSocket);
         return error("Error sending to proxy");
     }
     char pchRet2[4];
-    if (!InterruptibleRecv(pchRet2, 4, SOCKS5_RECV_TIMEOUT, hSocket))
-    {
+    if (!InterruptibleRecv(pchRet2, 4, SOCKS5_RECV_TIMEOUT, hSocket)) {
         CloseSocket(hSocket);
         return error("Error reading proxy response");
     }
-    if (pchRet2[0] != 0x05)
-    {
+    if (pchRet2[0] != 0x05) {
         CloseSocket(hSocket);
         return error("Proxy failed to accept request");
     }
-    if (pchRet2[1] != 0x00)
-    {
+    if (pchRet2[1] != 0x00) {
         CloseSocket(hSocket);
         switch (pchRet2[1])
         {
@@ -352,8 +394,7 @@ bool static Socks5(string strDest, int port, SOCKET& hSocket)
             default:   return error("Proxy error: unknown");
         }
     }
-    if (pchRet2[2] != 0x00)
-    {
+    if (pchRet2[2] != 0x00) {
         CloseSocket(hSocket);
         return error("Error: malformed proxy response");
     }
@@ -375,13 +416,11 @@ bool static Socks5(string strDest, int port, SOCKET& hSocket)
         }
         default: CloseSocket(hSocket); return error("Error: malformed proxy response");
     }
-    if (!ret)
-    {
+    if (!ret) {
         CloseSocket(hSocket);
         return error("Error reading from proxy");
     }
-    if (!InterruptibleRecv(pchRet3, 2, SOCKS5_RECV_TIMEOUT, hSocket))
-    {
+    if (!InterruptibleRecv(pchRet3, 2, SOCKS5_RECV_TIMEOUT, hSocket)) {
         CloseSocket(hSocket);
         return error("Error reading from proxy");
     }
@@ -471,7 +510,7 @@ bool static ConnectSocketDirectly(const CService &addrConnect, SOCKET& hSocketRe
     return true;
 }
 
-bool SetProxy(enum Network net, CService addrProxy) {
+bool SetProxy(enum Network net, const proxyType &addrProxy) {
     assert(net >= 0 && net < NET_MAX);
     if (!addrProxy.IsValid())
         return false;
@@ -489,7 +528,7 @@ bool GetProxy(enum Network net, proxyType &proxyInfoOut) {
     return true;
 }
 
-bool SetNameProxy(CService addrProxy) {
+bool SetNameProxy(const proxyType &addrProxy) {
     if (!addrProxy.IsValid())
         return false;
     LOCK(cs_proxyInfos);
@@ -497,7 +536,7 @@ bool SetNameProxy(CService addrProxy) {
     return true;
 }
 
-bool GetNameProxy(CService &nameProxyOut) {
+bool GetNameProxy(proxyType &nameProxyOut) {
     LOCK(cs_proxyInfos);
     if(!nameProxy.IsValid())
         return false;
@@ -513,37 +552,49 @@ bool HaveNameProxy() {
 bool IsProxy(const CNetAddr &addr) {
     LOCK(cs_proxyInfos);
     for (int i = 0; i < NET_MAX; i++) {
-        if (addr == (CNetAddr)proxyInfo[i])
+        if (addr == (CNetAddr)proxyInfo[i].proxy)
             return true;
     }
     return false;
 }
 
-bool ConnectSocket(const CService &addrDest, SOCKET& hSocketRet, int nTimeout, bool *outProxyConnectionFailed)
+static bool ConnectThroughProxy(const proxyType &proxy, const std::string strDest, int port, SOCKET& hSocketRet, int nTimeout, bool *outProxyConnectionFailed)
 {
-    proxyType proxy;
-    if (outProxyConnectionFailed)
-        *outProxyConnectionFailed = false;
-    // no proxy needed (none set for target network)
-    if (!GetProxy(addrDest.GetNetwork(), proxy))
-        return ConnectSocketDirectly(addrDest, hSocketRet, nTimeout);
-
     SOCKET hSocket = INVALID_SOCKET;
-
     // first connect to proxy server
-    if (!ConnectSocketDirectly(proxy, hSocket, nTimeout)) {
+    if (!ConnectSocketDirectly(proxy.proxy, hSocket, nTimeout)) {
         if (outProxyConnectionFailed)
             *outProxyConnectionFailed = true;
         return false;
     }
     // do socks negotiation
-    if (!Socks5(addrDest.ToStringIP(), addrDest.GetPort(), hSocket))
-        return false;
+    if (proxy.randomize_credentials) {
+        ProxyCredentials random_auth;
+        random_auth.username = strprintf("%i", insecure_rand());
+        random_auth.password = strprintf("%i", insecure_rand());
+        if (!Socks5(strDest, (unsigned short)port, &random_auth, hSocket))
+            return false;
+    } else {
+        if (!Socks5(strDest, (unsigned short)port, 0, hSocket))
+            return false;
+    }
 
     hSocketRet = hSocket;
     return true;
 }
 
+bool ConnectSocket(const CService &addrDest, SOCKET& hSocketRet, int nTimeout, bool *outProxyConnectionFailed)
+{
+    proxyType proxy;
+    if (outProxyConnectionFailed)
+        *outProxyConnectionFailed = false;
+
+    if (GetProxy(addrDest.GetNetwork(), proxy))
+        return ConnectThroughProxy(proxy, addrDest.ToStringIP(), addrDest.GetPort(), hSocketRet, nTimeout, outProxyConnectionFailed);
+    else // no proxy needed (none set for target network)
+        return ConnectSocketDirectly(addrDest, hSocketRet, nTimeout);
+}
+
 bool ConnectSocketByName(CService &addr, SOCKET& hSocketRet, const char *pszDest, int portDefault, int nTimeout, bool *outProxyConnectionFailed)
 {
     string strDest;
@@ -554,9 +605,7 @@ bool ConnectSocketByName(CService &addr, SOCKET& hSocketRet, const char *pszDest
 
     SplitHostPort(string(pszDest), port, strDest);
 
-    SOCKET hSocket = INVALID_SOCKET;
-
-    CService nameProxy;
+    proxyType nameProxy;
     GetNameProxy(nameProxy);
 
     CService addrResolved(CNetAddr(strDest, fNameLookup && !HaveNameProxy()), port);
@@ -569,18 +618,7 @@ bool ConnectSocketByName(CService &addr, SOCKET& hSocketRet, const char *pszDest
 
     if (!HaveNameProxy())
         return false;
-    // first connect to name proxy server
-    if (!ConnectSocketDirectly(nameProxy, hSocket, nTimeout)) {
-        if (outProxyConnectionFailed)
-            *outProxyConnectionFailed = true;
-        return false;
-    }
-    // do socks negotiation
-    if (!Socks5(strDest, (unsigned short)port, hSocket))
-        return false;
-
-    hSocketRet = hSocket;
-    return true;
+    return ConnectThroughProxy(nameProxy, strDest, port, hSocketRet, nTimeout, outProxyConnectionFailed);
 }
 
 void CNetAddr::Init()
diff --git a/src/netbase.h b/src/netbase.h
index b42c2dffa4..6d2ca4afb2 100644
--- a/src/netbase.h
+++ b/src/netbase.h
@@ -168,15 +168,25 @@ class CService : public CNetAddr
         }
 };
 
-typedef CService proxyType;
+class proxyType
+{
+public:
+    proxyType(): randomize_credentials(false) {}
+    proxyType(const CService &proxy, bool randomize_credentials=false): proxy(proxy), randomize_credentials(randomize_credentials) {}
+
+    bool IsValid() const { return proxy.IsValid(); }
+
+    CService proxy;
+    bool randomize_credentials;
+};
 
 enum Network ParseNetwork(std::string net);
 std::string GetNetworkName(enum Network net);
 void SplitHostPort(std::string in, int &portOut, std::string &hostOut);
-bool SetProxy(enum Network net, CService addrProxy);
+bool SetProxy(enum Network net, const proxyType &addrProxy);
 bool GetProxy(enum Network net, proxyType &proxyInfoOut);
 bool IsProxy(const CNetAddr &addr);
-bool SetNameProxy(CService addrProxy);
+bool SetNameProxy(const proxyType &addrProxy);
 bool HaveNameProxy();
 bool LookupHost(const char *pszName, std::vector<CNetAddr>& vIP, unsigned int nMaxSolutions = 0, bool fAllowLookup = true);
 bool Lookup(const char *pszName, CService& addr, int portDefault = 0, bool fAllowLookup = true);
diff --git a/src/qt/optionsmodel.cpp b/src/qt/optionsmodel.cpp
index a169ed6b55..41d6acf358 100644
--- a/src/qt/optionsmodel.cpp
+++ b/src/qt/optionsmodel.cpp
@@ -335,8 +335,8 @@ bool OptionsModel::getProxySettings(QNetworkProxy& proxy) const
     proxyType curProxy;
     if (GetProxy(NET_IPV4, curProxy)) {
         proxy.setType(QNetworkProxy::Socks5Proxy);
-        proxy.setHostName(QString::fromStdString(curProxy.ToStringIP()));
-        proxy.setPort(curProxy.GetPort());
+        proxy.setHostName(QString::fromStdString(curProxy.proxy.ToStringIP()));
+        proxy.setPort(curProxy.proxy.GetPort());
 
         return true;
     }
diff --git a/src/rpcmisc.cpp b/src/rpcmisc.cpp
index 938d79513f..f5bef2a077 100644
--- a/src/rpcmisc.cpp
+++ b/src/rpcmisc.cpp
@@ -90,7 +90,7 @@ Value getinfo(const Array& params, bool fHelp)
     obj.push_back(Pair("blocks",        (int)chainActive.Height()));
     obj.push_back(Pair("timeoffset",    GetTimeOffset()));
     obj.push_back(Pair("connections",   (int)vNodes.size()));
-    obj.push_back(Pair("proxy",         (proxy.IsValid() ? proxy.ToStringIPPort() : string())));
+    obj.push_back(Pair("proxy",         (proxy.IsValid() ? proxy.proxy.ToStringIPPort() : string())));
     obj.push_back(Pair("difficulty",    (double)GetDifficulty()));
     obj.push_back(Pair("testnet",       Params().TestnetToBeDeprecatedFieldRPC()));
 #ifdef ENABLE_WALLET
diff --git a/src/rpcnet.cpp b/src/rpcnet.cpp
index 6306fd4406..bdee5b9f2e 100644
--- a/src/rpcnet.cpp
+++ b/src/rpcnet.cpp
@@ -371,7 +371,8 @@ static Array GetNetworksInfo()
         obj.push_back(Pair("name", GetNetworkName(network)));
         obj.push_back(Pair("limited", IsLimited(network)));
         obj.push_back(Pair("reachable", IsReachable(network)));
-        obj.push_back(Pair("proxy", proxy.IsValid() ? proxy.ToStringIPPort() : string()));
+        obj.push_back(Pair("proxy", proxy.IsValid() ? proxy.proxy.ToStringIPPort() : string()));
+        obj.push_back(Pair("proxy_randomize_credentials", proxy.randomize_credentials));
         networks.push_back(obj);
     }
     return networks;