27 files changed, 348 insertions, 104 deletions

diff --git a/bitcoin-qt.pro b/bitcoin-qt.pro
index 7444ff4ac1..66b53c2367 100644
--- a/bitcoin-qt.pro
+++ b/bitcoin-qt.pro
@@ -88,6 +88,7 @@ HEADERS += src/qt/bitcoingui.h \
     src/qt/bitcoinaddressvalidator.h \
     src/base58.h \
     src/bignum.h \
+    src/checkpoints.h \
     src/util.h \
     src/uint256.h \
     src/serialize.h \
@@ -152,6 +153,7 @@ SOURCES += src/qt/bitcoin.cpp src/qt/bitcoingui.cpp \
     src/init.cpp \
     src/net.cpp \
     src/irc.cpp \
+    src/checkpoints.cpp \
     src/db.cpp \
     src/json/json_spirit_writer.cpp \
     src/json/json_spirit_value.cpp \
@@ -249,7 +251,7 @@ isEmpty(BOOST_INCLUDE_PATH) {
     macx:BOOST_INCLUDE_PATH = /opt/local/include
 }
 
-windows:LIBS += -lws2_32 -lgdi32
+windows:LIBS += -lws2_32
 windows:DEFINES += WIN32
 windows:RC_FILE = src/qt/res/bitcoin-qt.rc
 
@@ -264,6 +266,8 @@ macx:TARGET = "Bitcoin-Qt"
 INCLUDEPATH += $$BOOST_INCLUDE_PATH $$BDB_INCLUDE_PATH $$OPENSSL_INCLUDE_PATH
 LIBS += $$join(BOOST_LIB_PATH,,-L,) $$join(BDB_LIB_PATH,,-L,) $$join(OPENSSL_LIB_PATH,,-L,)
 LIBS += -lssl -lcrypto -ldb_cxx$$BDB_LIB_SUFFIX
+# -lgdi32 has to happen after -lcrypto (see  #681)
+windows:LIBS += -lgdi32
 LIBS += -lboost_system$$BOOST_LIB_SUFFIX -lboost_filesystem$$BOOST_LIB_SUFFIX -lboost_program_options$$BOOST_LIB_SUFFIX -lboost_thread$$BOOST_THREAD_LIB_SUFFIX
 
 contains(RELEASE, 1) {
diff --git a/src/bitcoinrpc.cpp b/src/bitcoinrpc.cpp
index 2857b7575e..bb8d8e2d77 100644
--- a/src/bitcoinrpc.cpp
+++ b/src/bitcoinrpc.cpp
@@ -36,6 +36,8 @@ void ThreadRPCServer2(void* parg);
 typedef Value(*rpcfn_type)(const Array& params, bool fHelp);
 extern map<string, rpcfn_type> mapCallTable;
 
+static std::string strRPCUserColonPass;
+
 static int64 nWalletUnlockTime;
 static CCriticalSection cs_nWalletUnlockTime;
 
@@ -1453,21 +1455,16 @@ Value walletpassphrase(const Array& params, bool fHelp)
         throw JSONRPCError(-17, "Error: Wallet is already unlocked.");
 
     // Note that the walletpassphrase is stored in params[0] which is not mlock()ed
-    string strWalletPass;
+    SecureString strWalletPass;
     strWalletPass.reserve(100);
-    mlock(&strWalletPass[0], strWalletPass.capacity());
-    strWalletPass = params[0].get_str();
+    // TODO: get rid of this .c_str() by implementing SecureString::operator=(std::string)
+    // Alternately, find a way to make params[0] mlock()'d to begin with.
+    strWalletPass = params[0].get_str().c_str();
 
     if (strWalletPass.length() > 0)
     {
         if (!pwalletMain->Unlock(strWalletPass))
-        {
-            fill(strWalletPass.begin(), strWalletPass.end(), '\0');
-            munlock(&strWalletPass[0], strWalletPass.capacity());
             throw JSONRPCError(-14, "Error: The wallet passphrase entered was incorrect.");
-        }
-        fill(strWalletPass.begin(), strWalletPass.end(), '\0');
-        munlock(&strWalletPass[0], strWalletPass.capacity());
     }
     else
         throw runtime_error(
@@ -1493,15 +1490,15 @@ Value walletpassphrasechange(const Array& params, bool fHelp)
     if (!pwalletMain->IsCrypted())
         throw JSONRPCError(-15, "Error: running with an unencrypted wallet, but walletpassphrasechange was called.");
 
-    string strOldWalletPass;
+    // TODO: get rid of these .c_str() calls by implementing SecureString::operator=(std::string)
+    // Alternately, find a way to make params[0] mlock()'d to begin with.
+    SecureString strOldWalletPass;
     strOldWalletPass.reserve(100);
-    mlock(&strOldWalletPass[0], strOldWalletPass.capacity());
-    strOldWalletPass = params[0].get_str();
+    strOldWalletPass = params[0].get_str().c_str();
 
-    string strNewWalletPass;
+    SecureString strNewWalletPass;
     strNewWalletPass.reserve(100);
-    mlock(&strNewWalletPass[0], strNewWalletPass.capacity());
-    strNewWalletPass = params[1].get_str();
+    strNewWalletPass = params[1].get_str().c_str();
 
     if (strOldWalletPass.length() < 1 || strNewWalletPass.length() < 1)
         throw runtime_error(
@@ -1509,17 +1506,7 @@ Value walletpassphrasechange(const Array& params, bool fHelp)
             "Changes the wallet passphrase from <oldpassphrase> to <newpassphrase>.");
 
     if (!pwalletMain->ChangeWalletPassphrase(strOldWalletPass, strNewWalletPass))
-    {
-        fill(strOldWalletPass.begin(), strOldWalletPass.end(), '\0');
-        fill(strNewWalletPass.begin(), strNewWalletPass.end(), '\0');
-        munlock(&strOldWalletPass[0], strOldWalletPass.capacity());
-        munlock(&strNewWalletPass[0], strNewWalletPass.capacity());
         throw JSONRPCError(-14, "Error: The wallet passphrase entered was incorrect.");
-    }
-    fill(strNewWalletPass.begin(), strNewWalletPass.end(), '\0');
-    fill(strOldWalletPass.begin(), strOldWalletPass.end(), '\0');
-    munlock(&strOldWalletPass[0], strOldWalletPass.capacity());
-    munlock(&strNewWalletPass[0], strNewWalletPass.capacity());
 
     return Value::null;
 }
@@ -1564,10 +1551,11 @@ Value encryptwallet(const Array& params, bool fHelp)
     throw runtime_error("Not Yet Implemented: use GUI to encrypt wallet, not RPC command");
 #endif
 
-    string strWalletPass;
+    // TODO: get rid of this .c_str() by implementing SecureString::operator=(std::string)
+    // Alternately, find a way to make params[0] mlock()'d to begin with.
+    SecureString strWalletPass;
     strWalletPass.reserve(100);
-    mlock(&strWalletPass[0], strWalletPass.capacity());
-    strWalletPass = params[0].get_str();
+    strWalletPass = params[0].get_str().c_str();
 
     if (strWalletPass.length() < 1)
         throw runtime_error(
@@ -1575,13 +1563,7 @@ Value encryptwallet(const Array& params, bool fHelp)
             "Encrypts the wallet with <passphrase>.");
 
     if (!pwalletMain->EncryptWallet(strWalletPass))
-    {
-        fill(strWalletPass.begin(), strWalletPass.end(), '\0');
-        munlock(&strWalletPass[0], strWalletPass.capacity());
         throw JSONRPCError(-16, "Error: Failed to encrypt the wallet.");
-    }
-    fill(strWalletPass.begin(), strWalletPass.end(), '\0');
-    munlock(&strWalletPass[0], strWalletPass.capacity());
 
     // BDB seems to have a bad habit of writing old data into
     // slack space in .dat files; that is bad if the old data is
@@ -2043,12 +2025,7 @@ bool HTTPAuthorized(map<string, string>& mapHeaders)
         return false;
     string strUserPass64 = strAuth.substr(6); boost::trim(strUserPass64);
     string strUserPass = DecodeBase64(strUserPass64);
-    string::size_type nColon = strUserPass.find(":");
-    if (nColon == string::npos)
-        return false;
-    string strUser = strUserPass.substr(0, nColon);
-    string strPassword = strUserPass.substr(nColon+1);
-    return (strUser == mapArgs["-rpcuser"] && strPassword == mapArgs["-rpcpassword"]);
+    return strUserPass == strRPCUserColonPass;
 }
 
 //
@@ -2181,7 +2158,8 @@ void ThreadRPCServer2(void* parg)
 {
     printf("ThreadRPCServer started\n");
 
-    if (mapArgs["-rpcuser"] == "" && mapArgs["-rpcpassword"] == "")
+    strRPCUserColonPass = mapArgs["-rpcuser"] + ":" + mapArgs["-rpcpassword"];
+    if (strRPCUserColonPass == ":")
     {
         string strWhatAmI = "To use bitcoind";
         if (mapArgs.count("-server"))
diff --git a/src/checkpoints.cpp b/src/checkpoints.cpp
new file mode 100644
index 0000000000..c7e054df37
--- /dev/null
+++ b/src/checkpoints.cpp
@@ -0,0 +1,65 @@
+// Copyright (c) 2011 The Bitcoin developers
+// Distributed under the MIT/X11 software license, see the accompanying
+// file license.txt or http://www.opensource.org/licenses/mit-license.php.
+
+#include <boost/assign/list_of.hpp> // for 'map_list_of()'
+#include <boost/foreach.hpp>
+
+#include "headers.h"
+#include "checkpoints.h"
+
+namespace Checkpoints
+{
+    typedef std::map<int, uint256> MapCheckpoints;
+
+    //
+    // What makes a good checkpoint block?
+    // + Is surrounded by blocks with reasonable timestamps
+    //   (no blocks before with a timestamp after, none after with
+    //    timestamp before)
+    // + Contains no strange transactions
+    //
+    static MapCheckpoints mapCheckpoints =
+        boost::assign::map_list_of
+        ( 11111, uint256("0x0000000069e244f73d78e8fd29ba2fd2ed618bd6fa2ee92559f542fdb26e7c1d"))
+        ( 33333, uint256("0x000000002dd5588a74784eaa7ab0507a18ad16a236e7b1ce69f00d7ddfb5d0a6"))
+        ( 68555, uint256("0x00000000001e1b4903550a0b96e9a9405c8a95f387162e4944e8d9fbe501cd6a"))
+        ( 70567, uint256("0x00000000006a49b14bcf27462068f1264c961f11fa2e0eddd2be0791e1d4124a"))
+        ( 74000, uint256("0x0000000000573993a3c9e41ce34471c079dcf5f52a0e824a81e7f953b8661a20"))
+        (105000, uint256("0x00000000000291ce28027faea320c8d2b054b2e0fe44a773f3eefb151d6bdc97"))
+        (118000, uint256("0x000000000000774a7f8a7a12dc906ddb9e17e75d684f15e00f8767f9e8f36553"))
+        (134444, uint256("0x00000000000005b12ffd4cd315cd34ffd4a594f430ac814c91184a0d42d2b0fe"))
+        (140700, uint256("0x000000000000033b512028abb90e1626d8b346fd0ed598ac0a3c371138dce2bd"))
+        ;
+
+    bool CheckBlock(int nHeight, const uint256& hash)
+    {
+        if (fTestNet) return true; // Testnet has no checkpoints
+
+        MapCheckpoints::const_iterator i = mapCheckpoints.find(nHeight);
+        if (i == mapCheckpoints.end()) return true;
+        return hash == i->second;
+    }
+
+    int GetTotalBlocksEstimate()
+    {
+        if (fTestNet) return 0;
+
+        return mapCheckpoints.rbegin()->first;
+    }
+
+    CBlockIndex* GetLastCheckpoint(const std::map<uint256, CBlockIndex*>& mapBlockIndex)
+    {
+        if (fTestNet) return NULL;
+
+        int64 nResult;
+        BOOST_REVERSE_FOREACH(const MapCheckpoints::value_type& i, mapCheckpoints)
+        {
+            const uint256& hash = i.second;
+            std::map<uint256, CBlockIndex*>::const_iterator t = mapBlockIndex.find(hash);
+            if (t != mapBlockIndex.end())
+                return t->second;
+        }
+        return NULL;
+    }
+}
diff --git a/src/checkpoints.h b/src/checkpoints.h
new file mode 100644
index 0000000000..9d52da404f
--- /dev/null
+++ b/src/checkpoints.h
@@ -0,0 +1,29 @@
+// Copyright (c) 2011 The Bitcoin developers
+// Distributed under the MIT/X11 software license, see the accompanying
+// file license.txt or http://www.opensource.org/licenses/mit-license.php.
+#ifndef BITCOIN_CHECKPOINT_H
+#define  BITCOIN_CHECKPOINT_H
+
+#include <map>
+#include "util.h"
+
+class uint256;
+class CBlockIndex;
+
+//
+// Block-chain checkpoints are compiled-in sanity checks.
+// They are updated every release or three.
+//
+namespace Checkpoints
+{
+    // Returns true if block passes checkpoint checks
+    bool CheckBlock(int nHeight, const uint256& hash);
+
+    // Return conservative estimate of total number of blocks, 0 if unknown
+    int GetTotalBlocksEstimate();
+
+    // Returns last CBlockIndex* in mapBlockIndex that is a checkpoint
+    CBlockIndex* GetLastCheckpoint(const std::map<uint256, CBlockIndex*>& mapBlockIndex);
+}
+
+#endif
diff --git a/src/crypter.cpp b/src/crypter.cpp
index bee7a3624b..7f53e22f1e 100644
--- a/src/crypter.cpp
+++ b/src/crypter.cpp
@@ -15,7 +15,7 @@
 #include "main.h"
 #include "util.h"
 
-bool CCrypter::SetKeyFromPassphrase(const std::string& strKeyData, const std::vector<unsigned char>& chSalt, const unsigned int nRounds, const unsigned int nDerivationMethod)
+bool CCrypter::SetKeyFromPassphrase(const SecureString& strKeyData, const std::vector<unsigned char>& chSalt, const unsigned int nRounds, const unsigned int nDerivationMethod)
 {
     if (nRounds < 1 || chSalt.size() != WALLET_CRYPTO_SALT_SIZE)
         return false;
diff --git a/src/crypter.h b/src/crypter.h
index e8ca30a8cc..d7f8a39d83 100644
--- a/src/crypter.h
+++ b/src/crypter.h
@@ -65,7 +65,7 @@ private:
     bool fKeySet;
 
 public:
-    bool SetKeyFromPassphrase(const std::string &strKeyData, const std::vector<unsigned char>& chSalt, const unsigned int nRounds, const unsigned int nDerivationMethod);
+    bool SetKeyFromPassphrase(const SecureString &strKeyData, const std::vector<unsigned char>& chSalt, const unsigned int nRounds, const unsigned int nDerivationMethod);
     bool Encrypt(const CKeyingMaterial& vchPlaintext, std::vector<unsigned char> &vchCiphertext);
     bool Decrypt(const std::vector<unsigned char>& vchCiphertext, CKeyingMaterial& vchPlaintext);
     bool SetKey(const CKeyingMaterial& chNewKey, const std::vector<unsigned char>& chNewIV);
diff --git a/src/init.cpp b/src/init.cpp
index a6d0ab56e3..dd8bdf5598 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -172,10 +172,10 @@ bool AppInit2(int argc, char* argv[])
         string strUsage = string() +
           _("Bitcoin version") + " " + FormatFullVersion() + "\n\n" +
           _("Usage:") + "\t\t\t\t\t\t\t\t\t\t\n" +
-            "  bitcoin [options]                   \t  " + "\n" +
-            "  bitcoin [options] <command> [params]\t  " + _("Send command to -server or bitcoind\n") +
-            "  bitcoin [options] help              \t\t  " + _("List commands\n") +
-            "  bitcoin [options] help <command>    \t\t  " + _("Get help for a command\n") +
+            "  bitcoind [options]                   \t  " + "\n" +
+            "  bitcoind [options] <command> [params]\t  " + _("Send command to -server or bitcoind\n") +
+            "  bitcoind [options] help              \t\t  " + _("List commands\n") +
+            "  bitcoind [options] help <command>    \t\t  " + _("Get help for a command\n") +
           _("Options:\n") +
             "  -conf=<file>     \t\t  " + _("Specify configuration file (default: bitcoin.conf)\n") +
             "  -pid=<file>      \t\t  " + _("Specify pid file (default: bitcoind.pid)\n") +
@@ -186,11 +186,16 @@ bool AppInit2(int argc, char* argv[])
             "  -timeout=<n>     \t  "   + _("Specify connection timeout (in milliseconds)\n") +
             "  -proxy=<ip:port> \t  "   + _("Connect through socks4 proxy\n") +
             "  -dns             \t  "   + _("Allow DNS lookups for addnode and connect\n") +
+            "  -port=<port>     \t\t  " + _("Listen for connections on <port> (default: 8333 or testnet: 18333)\n") +
+            "  -maxconnections=<n>\t  " + _("Maintain at most <n> connections to peers (default: 125)\n") +
             "  -addnode=<ip>    \t  "   + _("Add a node to connect to\n") +
             "  -connect=<ip>    \t\t  " + _("Connect only to the specified node\n") +
             "  -nolisten        \t  "   + _("Don't accept connections from outside\n") +
+            "  -nodnsseed       \t  "   + _("Don't bootstrap list of peers using DNS\n") +
             "  -banscore=<n>    \t  "   + _("Threshold for disconnecting misbehaving peers (default: 100)\n") +
             "  -bantime=<n>     \t  "   + _("Number of seconds to keep misbehaving peers from reconnecting (default: 86400)\n") +
+            "  -maxreceivebuffer=<n>\t  " + _("Maximum per-connection receive buffer, <n>*1000 bytes (default: 10000)\n") +
+            "  -maxsendbuffer=<n>\t  "   + _("Maximum per-connection send buffer, <n>*1000 bytes (default: 10000)\n") +
 #ifdef USE_UPNP
 #if USE_UPNP
             "  -noupnp          \t  "   + _("Don't attempt to use UPnP to map the listening port\n") +
@@ -206,6 +211,12 @@ bool AppInit2(int argc, char* argv[])
             "  -daemon          \t\t  " + _("Run in the background as a daemon and accept commands\n") +
 #endif
             "  -testnet         \t\t  " + _("Use the test network\n") +
+            "  -debug           \t\t  " + _("Output extra debugging information\n") +
+            "  -logtimestamps   \t  "   + _("Prepend debug output with timestamp\n") +
+            "  -printtoconsole  \t  "   + _("Send trace/debug info to console instead of debug.log file\n") +
+#ifdef WIN32
+            "  -printtodebugger \t  "   + _("Send trace/debug info to debugger\n") +
+#endif
             "  -rpcuser=<user>  \t  "   + _("Username for JSON-RPC connections\n") +
             "  -rpcpassword=<pw>\t  "   + _("Password for JSON-RPC connections\n") +
             "  -rpcport=<port>  \t\t  " + _("Listen for JSON-RPC connections on <port> (default: 8332)\n") +
@@ -476,11 +487,6 @@ bool AppInit2(int argc, char* argv[])
         }
     }
 
-    if (GetBoolArg("-nodnsseed"))
-        printf("DNS seeding disabled\n");
-    else
-        DNSAddressSeed();
-
     if (mapArgs.count("-paytxfee"))
     {
         if (!ParseMoney(mapArgs["-paytxfee"], nTransactionFee))
diff --git a/src/main.cpp b/src/main.cpp
index 47f1090727..a7871fcc16 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -3,6 +3,7 @@
 // Distributed under the MIT/X11 software license, see the accompanying
 // file license.txt or http://www.opensource.org/licenses/mit-license.php.
 #include "headers.h"
+#include "checkpoints.h"
 #include "db.h"
 #include "net.h"
 #include "init.h"
@@ -29,7 +30,6 @@ map<COutPoint, CInPoint> mapNextTx;
 map<uint256, CBlockIndex*> mapBlockIndex;
 uint256 hashGenesisBlock("0x000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f");
 static CBigNum bnProofOfWorkLimit(~uint256(0) >> 32);
-const int nTotalBlocksEstimate = 140700; // Conservative estimate of total nr of blocks on main chain
 const int nInitialBlockThreshold = 120; // Regard blocks up until N-threshold as "initial download"
 CBlockIndex* pindexGenesisBlock = NULL;
 int nBestHeight = -1;
@@ -659,11 +659,32 @@ int64 static GetBlockValue(int nHeight, int64 nFees)
     return nSubsidy + nFees;
 }
 
+static const int64 nTargetTimespan = 14 * 24 * 60 * 60; // two weeks
+static const int64 nTargetSpacing = 10 * 60;
+static const int64 nInterval = nTargetTimespan / nTargetSpacing;
+
+//
+// minimum amount of work that could possibly be required nTime after
+// minimum work required was nBase
+//
+unsigned int ComputeMinWork(unsigned int nBase, int64 nTime)
+{
+    CBigNum bnResult;
+    bnResult.SetCompact(nBase);
+    while (nTime > 0 && bnResult < bnProofOfWorkLimit)
+    {
+        // Maximum 400% adjustment...
+        bnResult *= 4;
+        // ... in best-case exactly 4-times-normal target time
+        nTime -= nTargetTimespan*4;
+    }
+    if (bnResult > bnProofOfWorkLimit)
+        bnResult = bnProofOfWorkLimit;
+    return bnResult.GetCompact();
+}
+
 unsigned int static GetNextWorkRequired(const CBlockIndex* pindexLast)
 {
-    const int64 nTargetTimespan = 14 * 24 * 60 * 60; // two weeks
-    const int64 nTargetSpacing = 10 * 60;
-    const int64 nInterval = nTargetTimespan / nTargetSpacing;
 
     // Genesis block
     if (pindexLast == NULL)
@@ -721,28 +742,15 @@ bool CheckProofOfWork(uint256 hash, unsigned int nBits)
     return true;
 }
 
-// Return conservative estimate of total number of blocks, 0 if unknown
-int GetTotalBlocksEstimate()
-{
-    if(fTestNet)
-    {
-        return 0;
-    }
-    else
-    {
-        return nTotalBlocksEstimate;
-    }
-}
-
 // Return maximum amount of blocks that other nodes claim to have
 int GetNumBlocksOfPeers()
 {
-    return std::max(cPeerBlockCounts.median(), GetTotalBlocksEstimate());
+    return std::max(cPeerBlockCounts.median(), Checkpoints::GetTotalBlocksEstimate());
 }
 
 bool IsInitialBlockDownload()
 {
-    if (pindexBest == NULL || nBestHeight < (GetTotalBlocksEstimate()-nInitialBlockThreshold))
+    if (pindexBest == NULL || nBestHeight < (Checkpoints::GetTotalBlocksEstimate()-nInitialBlockThreshold))
         return true;
     static int64 nLastUpdate;
     static CBlockIndex* pindexLastBest;
@@ -1317,17 +1325,8 @@ bool CBlock::AcceptBlock()
             return DoS(10, error("AcceptBlock() : contains a non-final transaction"));
 
     // Check that the block chain matches the known block chain up to a checkpoint
-    if (!fTestNet)
-        if ((nHeight ==  11111 && hash != uint256("0x0000000069e244f73d78e8fd29ba2fd2ed618bd6fa2ee92559f542fdb26e7c1d")) ||
-            (nHeight ==  33333 && hash != uint256("0x000000002dd5588a74784eaa7ab0507a18ad16a236e7b1ce69f00d7ddfb5d0a6")) ||
-            (nHeight ==  68555 && hash != uint256("0x00000000001e1b4903550a0b96e9a9405c8a95f387162e4944e8d9fbe501cd6a")) ||
-            (nHeight ==  70567 && hash != uint256("0x00000000006a49b14bcf27462068f1264c961f11fa2e0eddd2be0791e1d4124a")) ||
-            (nHeight ==  74000 && hash != uint256("0x0000000000573993a3c9e41ce34471c079dcf5f52a0e824a81e7f953b8661a20")) ||
-            (nHeight == 105000 && hash != uint256("0x00000000000291ce28027faea320c8d2b054b2e0fe44a773f3eefb151d6bdc97")) ||
-            (nHeight == 118000 && hash != uint256("0x000000000000774a7f8a7a12dc906ddb9e17e75d684f15e00f8767f9e8f36553")) ||
-            (nHeight == 134444 && hash != uint256("0x00000000000005b12ffd4cd315cd34ffd4a594f430ac814c91184a0d42d2b0fe")) ||
-            (nHeight == 140700 && hash != uint256("0x000000000000033b512028abb90e1626d8b346fd0ed598ac0a3c371138dce2bd")))
-            return DoS(100, error("AcceptBlock() : rejected by checkpoint lockin at %d", nHeight));
+    if (!Checkpoints::CheckBlock(nHeight, hash))
+        return DoS(100, error("AcceptBlock() : rejected by checkpoint lockin at %d", nHeight));
 
     // Write block to history file
     if (!CheckDiskSpace(::GetSerializeSize(*this, SER_DISK)))
@@ -1362,6 +1361,28 @@ bool ProcessBlock(CNode* pfrom, CBlock* pblock)
     if (!pblock->CheckBlock())
         return error("ProcessBlock() : CheckBlock FAILED");
 
+    CBlockIndex* pcheckpoint = Checkpoints::GetLastCheckpoint(mapBlockIndex);
+    if (pcheckpoint && pblock->hashPrevBlock != hashBestChain)
+    {
+        // Extra checks to prevent "fill up memory by spamming with bogus blocks"
+        int64 deltaTime = pblock->GetBlockTime() - pcheckpoint->nTime;
+        if (deltaTime < 0)
+        {
+            pfrom->Misbehaving(100);
+            return error("ProcessBlock() : block with timestamp before last checkpoint");
+        }
+        CBigNum bnNewBlock;
+        bnNewBlock.SetCompact(pblock->nBits);
+        CBigNum bnRequired;
+        bnRequired.SetCompact(ComputeMinWork(pcheckpoint->nBits, deltaTime));
+        if (bnNewBlock > bnRequired)
+        {
+            pfrom->Misbehaving(100);
+            return error("ProcessBlock() : block with too little proof-of-work");
+        }
+    }
+
+
     // If don't already have its previous block, shunt it off to holding area until we get it
     if (!mapBlockIndex.count(pblock->hashPrevBlock))
     {
diff --git a/src/main.h b/src/main.h
index 60ca318381..3870cee864 100644
--- a/src/main.h
+++ b/src/main.h
@@ -99,7 +99,7 @@ void IncrementExtraNonce(CBlock* pblock, CBlockIndex* pindexPrev, unsigned int&
 void FormatHashBuffers(CBlock* pblock, char* pmidstate, char* pdata, char* phash1);
 bool CheckWork(CBlock* pblock, CWallet& wallet, CReserveKey& reservekey);
 bool CheckProofOfWork(uint256 hash, unsigned int nBits);
-int GetTotalBlocksEstimate();
+unsigned int ComputeMinWork(unsigned int nBase, int64 nTime);
 int GetNumBlocksOfPeers();
 bool IsInitialBlockDownload();
 std::string GetWarnings(std::string strFor);
diff --git a/src/makefile.linux-mingw b/src/makefile.linux-mingw
index 29b433f851..61f8d4881f 100644
--- a/src/makefile.linux-mingw
+++ b/src/makefile.linux-mingw
@@ -32,6 +32,7 @@ CFLAGS=-O2 -w -Wno-invalid-offsetof -Wformat $(DEBUGFLAGS) $(DEFS) $(INCLUDEPATH
 HEADERS = \
     base58.h \
     bignum.h \
+    checkpoints.h \
     crypter.h \
     db.h \
     headers.h \
@@ -61,6 +62,7 @@ endif
 LIBS += -l mingwthrd -l kernel32 -l user32 -l gdi32 -l comdlg32 -l winspool -l winmm -l shell32 -l comctl32 -l ole32 -l oleaut32 -l uuid -l rpcrt4 -l advapi32 -l ws2_32 -l shlwapi
 
 OBJS= \
+    obj/checkpoints.o \
     obj/crypter.o \
     obj/db.o \
     obj/init.o \
diff --git a/src/makefile.mingw b/src/makefile.mingw
index 95d09f8770..2cb78d97e6 100644
--- a/src/makefile.mingw
+++ b/src/makefile.mingw
@@ -29,6 +29,7 @@ CFLAGS=-mthreads -O2 -w -Wno-invalid-offsetof -Wformat $(DEBUGFLAGS) $(DEFS) $(I
 HEADERS = \
     base58.h \
     bignum.h \
+    checkpoints.h \
     crypter.h \
     db.h \
     headers.h \
@@ -58,6 +59,7 @@ endif
 LIBS += -l kernel32 -l user32 -l gdi32 -l comdlg32 -l winspool -l winmm -l shell32 -l comctl32 -l ole32 -l oleaut32 -l uuid -l rpcrt4 -l advapi32 -l ws2_32 -l shlwapi
 
 OBJS= \
+    obj/checkpoints.o \
     obj/crypter.o \
     obj/db.o \
     obj/init.o \
diff --git a/src/makefile.osx b/src/makefile.osx
index 7830f3bad5..de71887935 100644
--- a/src/makefile.osx
+++ b/src/makefile.osx
@@ -49,6 +49,7 @@ CFLAGS=-mmacosx-version-min=10.5 -arch i386 -O3 -Wno-invalid-offsetof -Wformat $
 HEADERS = \
     base58.h \
     bignum.h \
+    checkpoints.h \
     crypter.h \
     db.h \
     headers.h \
@@ -69,6 +70,7 @@ HEADERS = \
     wallet.h
 
 OBJS= \
+    obj/checkpoints.o \
     obj/crypter.o \
     obj/db.o \
     obj/init.o \
diff --git a/src/makefile.unix b/src/makefile.unix
index 5f841ea0fe..6c48199546 100644
--- a/src/makefile.unix
+++ b/src/makefile.unix
@@ -87,6 +87,7 @@ xCXXFLAGS=-pthread -Wno-invalid-offsetof -Wformat $(DEBUGFLAGS) $(DEFS) $(HARDEN
 HEADERS = \
     base58.h \
     bignum.h \
+    checkpoints.h \
     crypter.h \
     db.h \
     headers.h \
@@ -107,6 +108,7 @@ HEADERS = \
     wallet.h
 
 OBJS= \
+    obj/checkpoints.o \
     obj/crypter.o \
     obj/db.o \
     obj/init.o \
diff --git a/src/makefile.vc b/src/makefile.vc
index c7e8578a95..60f1e09633 100644
--- a/src/makefile.vc
+++ b/src/makefile.vc
@@ -43,6 +43,7 @@ CFLAGS=/MD /c /nologo /EHsc /GR /Zm300 $(DEBUGFLAGS) $(DEFS) $(INCLUDEPATHS)
 HEADERS = \
     base58.h \
     bignum.h \
+    checkpoints.h \
     crypter.h \
     db.h \
     headers.h \
@@ -65,6 +66,7 @@ HEADERS = \
     wallet.h
 
 OBJS= \
+    obj\checkpoints.o \
     obj\crypter.o \
     obj\db.o \
     obj\init.o \
@@ -87,6 +89,8 @@ all: bitcoind.exe
 .cpp{obj}.obj:
     cl $(CFLAGS) /DGUI /Fo$@ %s
 
+obj\checkpoints.obj: $(HEADERS)
+
 obj\util.obj: $(HEADERS)
 
 obj\script.obj: $(HEADERS)
@@ -116,6 +120,8 @@ obj\uibase.obj: $(HEADERS)
 .cpp{obj\nogui}.obj:
     cl $(CFLAGS) /Fo$@ %s
 
+obj\nogui\checkpoints.obj: $(HEADERS)
+
 obj\nogui\util.obj: $(HEADERS)
 
 obj\nogui\script.obj: $(HEADERS)
diff --git a/src/net.cpp b/src/net.cpp
index 0c28eaa379..199fb407f2 100644
--- a/src/net.cpp
+++ b/src/net.cpp
@@ -32,6 +32,7 @@ void ThreadOpenConnections2(void* parg);
 #ifdef USE_UPNP
 void ThreadMapPort2(void* parg);
 #endif
+void ThreadDNSAddressSeed2(void* parg);
 bool OpenNetworkConnection(const CAddress& addrConnect);
 
 
@@ -1213,8 +1214,28 @@ static const char *strDNSSeed[] = {
     "dnsseed.bluematt.me",
 };
 
-void DNSAddressSeed()
+void ThreadDNSAddressSeed(void* parg)
 {
+    IMPLEMENT_RANDOMIZE_STACK(ThreadDNSAddressSeed(parg));
+    try
+    {
+        vnThreadsRunning[6]++;
+        ThreadDNSAddressSeed2(parg);
+        vnThreadsRunning[6]--;
+    }
+    catch (std::exception& e) {
+        vnThreadsRunning[6]--;
+        PrintException(&e, "ThreadDNSAddressSeed()");
+    } catch (...) {
+        vnThreadsRunning[6]--;
+        throw; // support pthread_cancel()
+    }
+    printf("ThreadDNSAddressSeed exiting\n");
+}
+
+void ThreadDNSAddressSeed2(void* parg)
+{
+    printf("ThreadDNSAddressSeed started\n");
     int found = 0;
 
     if (!fTestNet)
@@ -1247,6 +1268,15 @@ void DNSAddressSeed()
 
 
 
+
+
+
+
+
+
+
+
+
 unsigned int pnSeed[] =
 {
     0x6884ac63, 0x3ffecead, 0x2919b953, 0x0942fe50, 0x7a1d922e, 0xcdd6734a, 0x953a5bb6, 0x2c46922e,
@@ -1757,6 +1787,12 @@ void StartNode(void* parg)
     // Start threads
     //
 
+    if (GetBoolArg("-nodnsseed"))
+        printf("DNS seeding disabled\n");
+    else
+        if (!CreateThread(ThreadDNSAddressSeed, NULL))
+            printf("Error: CreateThread(ThreadDNSAddressSeed) failed\n");
+
     // Map ports with UPnP
     if (fHaveUPnP)
         MapPort(fUseUPnP);
@@ -1803,6 +1839,7 @@ bool StopNode()
     if (vnThreadsRunning[3] > 0) printf("ThreadBitcoinMiner still running\n");
     if (vnThreadsRunning[4] > 0) printf("ThreadRPCServer still running\n");
     if (fHaveUPnP && vnThreadsRunning[5] > 0) printf("ThreadMapPort still running\n");
+    if (vnThreadsRunning[6] > 0) printf("ThreadDNSAddressSeed still running\n");
     while (vnThreadsRunning[2] > 0 || vnThreadsRunning[4] > 0)
         Sleep(20);
     Sleep(50);
diff --git a/src/net.h b/src/net.h
index d847268999..03da382df3 100644
--- a/src/net.h
+++ b/src/net.h
@@ -40,7 +40,6 @@ CNode* ConnectNode(CAddress addrConnect, int64 nTimeout=0);
 void AbandonRequests(void (*fn)(void*, CDataStream&), void* param1);
 bool AnySubscribed(unsigned int nChannel);
 void MapPort(bool fMapPort);
-void DNSAddressSeed();
 bool BindListenPort(std::string& strError=REF(std::string()));
 void StartNode(void* parg);
 bool StopNode();
diff --git a/src/qt/askpassphrasedialog.cpp b/src/qt/askpassphrasedialog.cpp
index a574ef925b..24f622d637 100644
--- a/src/qt/askpassphrasedialog.cpp
+++ b/src/qt/askpassphrasedialog.cpp
@@ -71,16 +71,17 @@ void AskPassphraseDialog::setModel(WalletModel *model)
 
 void AskPassphraseDialog::accept()
 {
-    std::string oldpass, newpass1, newpass2;
+    SecureString oldpass, newpass1, newpass2;
     if(!model)
         return;
-    // TODO: mlock memory / munlock on return so they will not be swapped out, really need "mlockedstring" wrapper class to do this safely
     oldpass.reserve(MAX_PASSPHRASE_SIZE);
     newpass1.reserve(MAX_PASSPHRASE_SIZE);
     newpass2.reserve(MAX_PASSPHRASE_SIZE);
-    oldpass.assign(ui->passEdit1->text().toStdString());
-    newpass1.assign(ui->passEdit2->text().toStdString());
-    newpass2.assign(ui->passEdit3->text().toStdString());
+    // TODO: get rid of this .c_str() by implementing SecureString::operator=(std::string)
+    // Alternately, find a way to make this input mlock()'d to begin with.
+    oldpass.assign(ui->passEdit1->text().toStdString().c_str());
+    newpass1.assign(ui->passEdit2->text().toStdString().c_str());
+    newpass2.assign(ui->passEdit3->text().toStdString().c_str());
 
     switch(mode)
     {
diff --git a/src/qt/res/icons/address-book.png b/src/qt/res/icons/address-book.png
index dbfc28ab3d..d41dbe6539 100644
--- a/src/qt/res/icons/address-book.png
+++ b/src/qt/res/icons/address-book.png
diff --git a/src/qt/res/icons/overview.png b/src/qt/res/icons/overview.png
index 3b90fe5569..ee2511f01d 100644
--- a/src/qt/res/icons/overview.png
+++ b/src/qt/res/icons/overview.png
diff --git a/src/qt/walletmodel.cpp b/src/qt/walletmodel.cpp
index 2f989661f0..f028f10f6c 100644
--- a/src/qt/walletmodel.cpp
+++ b/src/qt/walletmodel.cpp
@@ -200,7 +200,7 @@ WalletModel::EncryptionStatus WalletModel::getEncryptionStatus() const
     }
 }
 
-bool WalletModel::setWalletEncrypted(bool encrypted, const std::string &passphrase)
+bool WalletModel::setWalletEncrypted(bool encrypted, const SecureString &passphrase)
 {
     if(encrypted)
     {
@@ -214,7 +214,7 @@ bool WalletModel::setWalletEncrypted(bool encrypted, const std::string &passphra
     }
 }
 
-bool WalletModel::setWalletLocked(bool locked, const std::string &passPhrase)
+bool WalletModel::setWalletLocked(bool locked, const SecureString &passPhrase)
 {
     if(locked)
     {
@@ -228,7 +228,7 @@ bool WalletModel::setWalletLocked(bool locked, const std::string &passPhrase)
     }
 }
 
-bool WalletModel::changePassphrase(const std::string &oldPass, const std::string &newPass)
+bool WalletModel::changePassphrase(const SecureString &oldPass, const SecureString &newPass)
 {
     bool retval;
     CRITICAL_BLOCK(wallet->cs_wallet)
diff --git a/src/qt/walletmodel.h b/src/qt/walletmodel.h
index 43b96f6d0e..89e8cdd2a0 100644
--- a/src/qt/walletmodel.h
+++ b/src/qt/walletmodel.h
@@ -2,7 +2,8 @@
 #define WALLETMODEL_H
 
 #include <QObject>
-#include <string>
+
+#include "util.h"
 
 class OptionsModel;
 class AddressTableModel;
@@ -72,10 +73,10 @@ public:
     SendCoinsReturn sendCoins(const QList<SendCoinsRecipient> &recipients);
 
     // Wallet encryption
-    bool setWalletEncrypted(bool encrypted, const std::string &passphrase);
+    bool setWalletEncrypted(bool encrypted, const SecureString &passphrase);
     // Passphrase only needed when unlocking
-    bool setWalletLocked(bool locked, const std::string &passPhrase=std::string());
-    bool changePassphrase(const std::string &oldPass, const std::string &newPass);
+    bool setWalletLocked(bool locked, const SecureString &passPhrase=SecureString());
+    bool changePassphrase(const SecureString &oldPass, const SecureString &newPass);
 
     // RAI object for unlocking wallet, returned by requestUnlock()
     class UnlockContext
diff --git a/src/test/Checkpoints_tests.cpp b/src/test/Checkpoints_tests.cpp
new file mode 100644
index 0000000000..0d8a366d7a
--- /dev/null
+++ b/src/test/Checkpoints_tests.cpp
@@ -0,0 +1,34 @@
+//
+// Unit tests for block-chain checkpoints
+//
+#include <boost/assign/list_of.hpp> // for 'map_list_of()'
+#include <boost/test/unit_test.hpp>
+#include <boost/foreach.hpp>
+
+#include "../checkpoints.h"
+#include "../util.h"
+
+using namespace std;
+
+BOOST_AUTO_TEST_SUITE(Checkpoints_tests)
+
+BOOST_AUTO_TEST_CASE(sanity)
+{
+    uint256 p11111 = uint256("0x0000000069e244f73d78e8fd29ba2fd2ed618bd6fa2ee92559f542fdb26e7c1d");
+    uint256 p140700 = uint256("0x000000000000033b512028abb90e1626d8b346fd0ed598ac0a3c371138dce2bd");
+    BOOST_CHECK(Checkpoints::CheckBlock(11111, p11111));
+    BOOST_CHECK(Checkpoints::CheckBlock(140700, p140700));
+
+    
+    // Wrong hashes at checkpoints should fail:
+    BOOST_CHECK(!Checkpoints::CheckBlock(11111, p140700));
+    BOOST_CHECK(!Checkpoints::CheckBlock(140700, p11111));
+
+    // ... but any hash not at a checkpoint should succeed:
+    BOOST_CHECK(Checkpoints::CheckBlock(11111+1, p140700));
+    BOOST_CHECK(Checkpoints::CheckBlock(140700+1, p11111));
+
+    BOOST_CHECK(Checkpoints::GetTotalBlocksEstimate() >= 140700);
+}    
+
+BOOST_AUTO_TEST_SUITE_END()
diff --git a/src/test/DoS_tests.cpp b/src/test/DoS_tests.cpp
index e60bb742dd..01e6691254 100644
--- a/src/test/DoS_tests.cpp
+++ b/src/test/DoS_tests.cpp
@@ -1,6 +1,7 @@
 //
 // Unit tests for denial-of-service detection/prevention code
 //
+#include <boost/assign/list_of.hpp> // for 'map_list_of()'
 #include <boost/test/unit_test.hpp>
 #include <boost/foreach.hpp>
 
@@ -64,5 +65,54 @@ BOOST_AUTO_TEST_CASE(DoS_bantime)
     BOOST_CHECK(!CNode::IsBanned(addr.ip));
 }    
 
+static bool CheckNBits(unsigned int nbits1, int64 time1, unsigned int nbits2, int64 time2)
+{
+    if (time1 > time2)
+        return CheckNBits(nbits2, time2, nbits1, time1);
+    int64 deltaTime = time2-time1;
+
+    CBigNum required;
+    required.SetCompact(ComputeMinWork(nbits1, deltaTime));
+    CBigNum have;
+    have.SetCompact(nbits2);
+    return (have <= required);
+}
+
+BOOST_AUTO_TEST_CASE(DoS_checknbits)
+{
+    using namespace boost::assign; // for 'map_list_of()'
+
+    // Timestamps,nBits from the bitcoin blockchain.
+    // These are the block-chain checkpoint blocks
+    typedef std::map<int64, unsigned int> BlockData;
+    BlockData chainData =
+        map_list_of(1239852051,486604799)(1262749024,486594666)
+        (1279305360,469854461)(1280200847,469830746)(1281678674,469809688)
+        (1296207707,453179945)(1302624061,453036989)(1309640330,437004818)
+        (1313172719,436789733);
+
+    // Make sure CheckNBits considers every combination of block-chain-lock-in-points
+    // "sane":
+    BOOST_FOREACH(const BlockData::value_type& i, chainData)
+    {
+        BOOST_FOREACH(const BlockData::value_type& j, chainData)
+        {
+            BOOST_CHECK(CheckNBits(i.second, i.first, j.second, j.first));
+        }
+    }
+
+    // Test a couple of insane combinations:
+    BlockData::value_type firstcheck = *(chainData.begin());
+    BlockData::value_type lastcheck = *(chainData.rbegin());
+
+    // First checkpoint difficulty at or a while after the last checkpoint time should fail when
+    // compared to last checkpoint
+    BOOST_CHECK(!CheckNBits(firstcheck.second, lastcheck.first+60*10, lastcheck.second, lastcheck.first));
+    BOOST_CHECK(!CheckNBits(firstcheck.second, lastcheck.first+60*60*24*14, lastcheck.second, lastcheck.first));
+
+    // ... but OK if enough time passed for difficulty to adjust downward:
+    BOOST_CHECK(CheckNBits(firstcheck.second, lastcheck.first+60*60*24*365*4, lastcheck.second, lastcheck.first));
+    
+}
 
 BOOST_AUTO_TEST_SUITE_END()
diff --git a/src/test/test_bitcoin.cpp b/src/test/test_bitcoin.cpp
index 8863aad478..39a7c88e13 100644
--- a/src/test/test_bitcoin.cpp
+++ b/src/test/test_bitcoin.cpp
@@ -13,6 +13,7 @@
 #include "util_tests.cpp"
 #include "base58_tests.cpp"
 #include "miner_tests.cpp"
+#include "Checkpoints_tests.cpp"
 
 CWallet* pwalletMain;
 
diff --git a/src/util.h b/src/util.h
index 4c966486f7..1ef0e6f15c 100644
--- a/src/util.h
+++ b/src/util.h
@@ -292,6 +292,10 @@ public:
 
 
 
+// This is exactly like std::string, but with a custom allocator.
+// (secure_allocator<> is defined in serialize.h)
+typedef std::basic_string<char, std::char_traits<char>, secure_allocator<char> > SecureString;
+
 
 
 
diff --git a/src/wallet.cpp b/src/wallet.cpp
index af80cc16d5..28babdb3e2 100644
--- a/src/wallet.cpp
+++ b/src/wallet.cpp
@@ -42,7 +42,7 @@ bool CWallet::AddCryptedKey(const vector<unsigned char> &vchPubKey, const vector
     return false;
 }
 
-bool CWallet::Unlock(const string& strWalletPassphrase)
+bool CWallet::Unlock(const SecureString& strWalletPassphrase)
 {
     if (!IsLocked())
         return false;
@@ -63,7 +63,7 @@ bool CWallet::Unlock(const string& strWalletPassphrase)
     return false;
 }
 
-bool CWallet::ChangeWalletPassphrase(const string& strOldWalletPassphrase, const string& strNewWalletPassphrase)
+bool CWallet::ChangeWalletPassphrase(const SecureString& strOldWalletPassphrase, const SecureString& strNewWalletPassphrase)
 {
     bool fWasLocked = IsLocked();
 
@@ -122,7 +122,7 @@ public:
     )
 };
 
-bool CWallet::EncryptWallet(const string& strWalletPassphrase)
+bool CWallet::EncryptWallet(const SecureString& strWalletPassphrase)
 {
     if (IsCrypted())
         return false;
diff --git a/src/wallet.h b/src/wallet.h
index 19de803390..ca7cf67317 100644
--- a/src/wallet.h
+++ b/src/wallet.h
@@ -70,9 +70,9 @@ public:
     // Adds an encrypted key to the store, without saving it to disk (used by LoadWallet)
     bool LoadCryptedKey(const std::vector<unsigned char> &vchPubKey, const std::vector<unsigned char> &vchCryptedSecret) { return CCryptoKeyStore::AddCryptedKey(vchPubKey, vchCryptedSecret); }
 
-    bool Unlock(const std::string& strWalletPassphrase);
-    bool ChangeWalletPassphrase(const std::string& strOldWalletPassphrase, const std::string& strNewWalletPassphrase);
-    bool EncryptWallet(const std::string& strWalletPassphrase);
+    bool Unlock(const SecureString& strWalletPassphrase);
+    bool ChangeWalletPassphrase(const SecureString& strOldWalletPassphrase, const SecureString& strNewWalletPassphrase);
+    bool EncryptWallet(const SecureString& strWalletPassphrase);
 
     bool AddToWallet(const CWalletTx& wtxIn);
     bool AddToWalletIfInvolvingMe(const CTransaction& tx, const CBlock* pblock, bool fUpdate = false);