Have bitcoind recommend a secure RPC password. Increase invalid password delay.

Help users avoid insecure configurations a bit by recommending a
secure RPC password and increasing the incorrect password delay.

This may open up a RPC DOS for users with exposed RPC ports and
short passwords. Since users shouldn't have exposed RPC ports OR
short passwords, the DOS risk is preferable to the compromise
risk.

Also logs the client IP address for incorrect attempts.

src/bitcoinrpc.cpp

@@ -2368,18 +2368,25 @@ void ThreadRPCServer2(void* parg)
     printf("ThreadRPCServer started\n");
 
     strRPCUserColonPass = mapArgs["-rpcuser"] + ":" + mapArgs["-rpcpassword"];
-    if (strRPCUserColonPass == ":")
+    if (mapArgs["-rpcpassword"] == "")
     {
+        unsigned char rand_pwd[32];
+        RAND_bytes(rand_pwd, 32);
         string strWhatAmI = "To use bitcoind";
         if (mapArgs.count("-server"))
             strWhatAmI = strprintf(_("To use the %s option"), "\"-server\"");
         else if (mapArgs.count("-daemon"))
             strWhatAmI = strprintf(_("To use the %s option"), "\"-daemon\"");
         PrintConsole(
-            _("Error: %s, you must set rpcpassword=<password>\nin the configuration file: %s\n"
+            _("Error: %s, you must set a rpcpassword in the configuration file:\n %s\n"
+              "It is recommended you use the following random password:\n"
+              "rpcuser=bitcoinrpc\n"
+              "rpcpassword=%s\n"
+              "(you do not need to remember this password)\n"
               "If the file does not exist, create it with owner-readable-only file permissions.\n"),
                 strWhatAmI.c_str(),
-                GetConfigFile().c_str());
+                GetConfigFile().c_str(),
+                EncodeBase58(&rand_pwd[0],&rand_pwd[0]+32).c_str());
 #ifndef QT_GUI
         CreateThread(Shutdown, NULL);
 #endif
@@ -2468,12 +2475,14 @@ void ThreadRPCServer2(void* parg)
         }
         if (!HTTPAuthorized(mapHeaders))
         {
-            // Deter brute-forcing short passwords
-            if (mapArgs["-rpcpassword"].size() < 15)
-                Sleep(50);
+            printf("ThreadRPCServer incorrect password attempt from %s\n",peer.address().to_string().c_str());
+            /* Deter brute-forcing short passwords.
+               If this results in a DOS the user really
+               shouldn't have their RPC port exposed.*/
+            if (mapArgs["-rpcpassword"].size() < 20)
+                Sleep(250);
 
             stream << HTTPReply(401, "") << std::flush;
-            printf("ThreadRPCServer incorrect password attempt\n");
             continue;
         }