Topic: PPCoin Criticism / Security / etc (Read 5861 times)

diff ../poscoin/src/checkpoints.cpp src/checkpoints.cpp
33c33
<         return true; // poscoin has no checkpoints
---
>         if (fTestNet) return true; // Testnet has no checkpoints
88d87
<         return true;
Only in ../poscoin/src: checkpoints.ppc
Common subdirectories: ../poscoin/src/json and src/json
diff ../poscoin/src/main.cpp src/main.cpp
866c866
<     return min(MIN_STAKE_REWARD,nSubsidy);
---
>     return nSubsidy;
1774c1774
<         bnCentSecond += CBigNum(nValueIn) * max(nTime-txPrev.nTime,COIN_AGE_CAP) / CENT;
---
>         bnCentSecond += CBigNum(nValueIn) * (nTime-txPrev.nTime) / CENT;
1875,1876c1875,1876
<     if ((nBestHeight > 10) && IsProofOfWork())
<         return DoS(50, error("CheckBlock() : proof of work is fail! :)"));
---
>     if (IsProofOfWork() && !CheckProofOfWork(GetHash(), nBits))
>         return DoS(50, error("CheckBlock() : proof of work failed"));
1979,1980c1979,1980
< //    if (!Checkpoints::CheckHardened(nHeight, hash))
< //        return DoS(100, error("AcceptBlock() : rejected by hardened checkpoint lockin at %d", nHeight));
---
>     if (!Checkpoints::CheckHardened(nHeight, hash))
>         return DoS(100, error("AcceptBlock() : rejected by hardened checkpoint lockin at %d", nHeight));
1983,1984c1983,1984
< //    if (!Checkpoints::CheckSync(hash, pindexPrev))
< //        return error("AcceptBlock() : rejected by synchronized checkpoint");
---
>     if (!Checkpoints::CheckSync(hash, pindexPrev))
>         return error("AcceptBlock() : rejected by synchronized checkpoint");
3601,3603d3600
<     if (nBestHeight < FIRST_STAKE_BLOCK)
< 	fProofOfStake = 0;
< 
diff ../poscoin/src/main.h src/main.h
35,37d34
< static const unsigned int COIN_AGE_CAP = 90 * 24 * 60 * 60;
< static const unsigned int FIRST_STAKE_BLOCK = 10;
< static const int64 MIN_STAKE_REWARD = COIN;
111c108
< CBlock* CreateNewBlock(CWallet* pwallet, bool fProofOfStake=true);
---
> CBlock* CreateNewBlock(CWallet* pwallet, bool fProofOfStake=false);
Common subdirectories: ../poscoin/src/obj and src/obj
Common subdirectories: ../poscoin/src/obj-test and src/obj-test
diff ../poscoin/src/protocol.cpp src/protocol.cpp
25,31c25,26
< //static unsigned char pchMessageStartBitcoin[4] = { 0xf9, 0xbe, 0xb4, 0xd9 };
< //static unsigned char pchMessageStartPPCoin[4] = { 0xe6, 0xe8, 0xe9, 0xe5 };
< //static unsigned int nMessageStartSwitchTime = 1347300000;
< 
< // POSoin message start
< static unsigned char pchMessageStartBitcoin[4] = { 'P', 'O', 'S', ':' };
< static unsigned char pchMessageStartPPCoin[4] = { 'P', 'O', 'S', ':' };
---
> static unsigned char pchMessageStartBitcoin[4] = { 0xf9, 0xbe, 0xb4, 0xd9 };
> static unsigned char pchMessageStartPPCoin[4] = { 0xe6, 0xe8, 0xe9, 0xe5 };
Common subdirectories: ../poscoin/src/qt and src/qt
Common subdirectories: ../poscoin/src/test and src/test

// ppcoin: miner's coin stake is rewarded based on coin age spent (coin-days)
int64 GetProofOfStakeReward(int64 nCoinAge)
{
    static int64 nRewardCoinYear = CENT;  // creation amount per coin-year
    int64 nSubsidy = nCoinAge * 33 / (365 * 33 + 8) * nRewardCoinYear;
    if (fDebug && GetBoolArg("-printcreation"))
        printf("GetProofOfStakeReward(): create=%s nCoinAge=%"PRI64d"\n", FormatMoney(nSubsidy).c_str(), nCoinAge);
    return nSubsidy;
}

static const int64 nTargetTimespan = 7 * 24 * 60 * 60;  // one week
static const int64 nTargetSpacingStake = 10 * 60;       // ten minutes
static const int64 nTargetSpacingWorkMax = 2 * 60 * 60; // two hours

unsigned int static GetNextTargetRequired(const CBlockIndex* pindexLast, bool fProofOfStake)
{
    if (pindexLast == NULL)
        return bnProofOfWorkLimit.GetCompact(); // genesis block

    const CBlockIndex* pindexPrev = GetLastBlockIndex(pindexLast, fProofOfStake);
    if (pindexPrev->pprev == NULL)
        return bnInitialHashTarget.GetCompact(); // first block
    const CBlockIndex* pindexPrevPrev = GetLastBlockIndex(pindexPrev->pprev, fProofOfStake);
    if (pindexPrevPrev->pprev == NULL)
        return bnInitialHashTarget.GetCompact(); // second block

    int64 nActualSpacing = pindexPrev->GetBlockTime() - pindexPrevPrev->GetBlockTime();

    // ppcoin: target change every block
    // ppcoin: retarget with exponential moving toward target spacing
    CBigNum bnNew;
    bnNew.SetCompact(pindexPrev->nBits);
    int64 nTargetSpacing = fProofOfStake? nTargetSpacingStake : min(nTargetSpacingWorkMax, nTargetSpacingStake * (1 + pindexLast->nHeight - pindexPrev->nHeight));
    int64 nInterval = nTargetTimespan / nTargetSpacing;
    bnNew *= ((nInterval - 1) * nTargetSpacing + nActualSpacing + nActualSpacing);
    bnNew /= ((nInterval + 1) * nTargetSpacing);

    if (bnNew > bnProofOfWorkLimit)
        bnNew = bnProofOfWorkLimit;

    return bnNew.GetCompact();
}

bool CTransaction::ConnectInputs(CTxDB& txdb, MapPrevTx inputs,
                                 map& mapTestPool, const CDiskTxPos& posThisTx,
                                 const CBlockIndex* pindexBlock, bool fBlock, bool fMiner, bool fStrictPayToScriptHash)
{
         ...
        if (IsCoinStake())
        {
            // ppcoin: coin stake tx earns reward instead of paying fee
            uint64 nCoinAge;
            if (!GetCoinAge(txdb, nCoinAge))
                return error("ConnectInputs() : %s unable to get coin age for coinstake", GetHash().ToString().substr(0,10).c_str());
            int64 nStakeReward = GetValueOut() - nValueIn;
            if (nStakeReward > GetProofOfStakeReward(nCoinAge) - GetMinFee() + MIN_TX_FEE)
                return DoS(100, error("ConnectInputs() : %s stake reward exceeded", GetHash().ToString().substr(0,10).c_str()));
        }
        else
        {
            if (nValueIn < GetValueOut())
                return DoS(100, error("ConnectInputs() : %s value in < value out", GetHash().ToString().substr(0,10).c_str()));

            // Tally transaction fees
            int64 nTxFee = nValueIn - GetValueOut();
            if (nTxFee < 0)
                return DoS(100, error("ConnectInputs() : %s nTxFee < 0", GetHash().ToString().substr(0,10).c_str()));
            // ppcoin: enforce transaction fees for every block
            if (nTxFee < GetMinFee())
                return fBlock? DoS(100, error("ConnectInputs() : %s not paying required fee=%s, paid=%s", GetHash().ToString().substr(0,10).c_str(), FormatMoney(GetMinFee()).c_str(), FormatMoney(nTxFee).c_str())) : false;
            nFees += nTxFee;
            if (!MoneyRange(nFees))
                return DoS(100, error("ConnectInputs() : nFees out of range"));
        }
    }

    return true;
}

// ppcoin: coinstake must meet hash target according to the protocol:
// kernel (input 0) must meet the formula
//     hash(nBits + txPrev.block.nTime + txPrev.offset + txPrev.nTime + txPrev.vout.n + nTime) < bnTarget * nCoinDay
// this ensures that the chance of getting a coinstake is proportional to the
// amount of coin age one owns.
// The reason this hash is chosen is the following:
//   nBits: encodes all past block timestamps, making computing hash in advance
//          more difficult
//   txPrev.block.nTime: prevent nodes from guessing a good timestamp to
//                       generate transaction for future advantage
//   txPrev.offset: offset of txPrev inside block, to reduce the chance of 
//                  nodes generating coinstake at the same time
//   txPrev.nTime: reduce the chance of nodes generating coinstake at the same
//                 time
//   txPrev.vout.n: output number of txPrev, to reduce the chance of nodes
//                  generating coinstake at the same time
//   block/tx hash should not be used here as they can be generated in vast
//   quantities so as to generate blocks faster, degrading the system back into
//   a proof-of-work situation.
//
bool CTransaction::CheckProofOfStake(unsigned int nBits) const
{
    CBigNum bnTargetPerCoinDay;
    bnTargetPerCoinDay.SetCompact(nBits);
 
    if (!IsCoinStake())
        return true;

    // Kernel (input 0) must match the stake hash target per coin age (nBits)
    const CTxIn& txin = vin[0];

    // First try finding the previous transaction in database
    CTxDB txdb("r");
    CTransaction txPrev;
    CTxIndex txindex;
    if (!txPrev.ReadFromDisk(txdb, txin.prevout, txindex))
        return false;  // previous transaction not in main chain
    txdb.Close();
    if (nTime < txPrev.nTime)
        return false;  // Transaction timestamp violation

    // Verify signature
    if (!VerifySignature(txPrev, *this, 0, true, 0))
        return DoS(100, error("CheckProofOfStake() : VerifySignature failed on coinstake %s", GetHash().ToString().c_str()));

    // Read block header
    CBlock block;
    if (!block.ReadFromDisk(txindex.pos.nFile, txindex.pos.nBlockPos, false))
        return false; // unable to read block of previous transaction
    if (block.GetBlockTime() + nStakeMinAge > nTime)
        return false; // only count coins meeting min age requirement

    int64 nValueIn = txPrev.vout[txin.prevout.n].nValue;
    CBigNum bnCoinDay = CBigNum(nValueIn) * min(nTime-txPrev.nTime, (unsigned int)STAKE_MAX_AGE) / COIN / (24 * 60 * 60);
    // Calculate hash
    CDataStream ss(SER_GETHASH, 0);
    ss << nBits << block.nTime << (txindex.pos.nTxPos - txindex.pos.nBlockPos) << txPrev.nTime << txin.prevout.n << nTime;
    if (CBigNum(Hash(ss.begin(), ss.end())) <= bnCoinDay * bnTargetPerCoinDay)
        return true;
    else
        return DoS(100, error("CheckProofOfStake() : check target failed on coinstake %s", GetHash().ToString().c_str()));
}

// ppcoin: total coin age spent in transaction, in the unit of coin-days.
// Only those coins meeting minimum age requirement counts. As those
// transactions not in main chain are not currently indexed so we
// might not find out about their coin age. Older transactions are 
// guaranteed to be in main chain by sync-checkpoint. This rule is
// introduced to help nodes establish a consistent view of the coin
// age (trust score) of competing branches.
bool CTransaction::GetCoinAge(CTxDB& txdb, uint64& nCoinAge) const
{
    CBigNum bnCentSecond = 0;  // coin age in the unit of cent-seconds
    nCoinAge = 0;

    if (IsCoinBase())
        return true;

    BOOST_FOREACH(const CTxIn& txin, vin)
    {
        // First try finding the previous transaction in database
        CTransaction txPrev;
        CTxIndex txindex;
        if (!txPrev.ReadFromDisk(txdb, txin.prevout, txindex))
            continue;  // previous transaction not in main chain
        if (nTime < txPrev.nTime)
            return false;  // Transaction timestamp violation

        // Read block header
        CBlock block;
        if (!block.ReadFromDisk(txindex.pos.nFile, txindex.pos.nBlockPos, false))
            return false; // unable to read block of previous transaction
        if (block.GetBlockTime() + nStakeMinAge > nTime)
            continue; // only count coins meeting min age requirement

        int64 nValueIn = txPrev.vout[txin.prevout.n].nValue;
        bnCentSecond += CBigNum(nValueIn) * (nTime-txPrev.nTime) / CENT;

        if (fDebug && GetBoolArg("-printcoinage"))
            printf("coin age nValueIn=%-12I64d nTimeDiff=%d bnCentSecond=%s\n", nValueIn, nTime - txPrev.nTime, bnCentSecond.ToString().c_str());
    }

    CBigNum bnCoinDay = bnCentSecond * CENT / COIN / (24 * 60 * 60);
    if (fDebug && GetBoolArg("-printcoinage"))
        printf("coin age bnCoinDay=%s\n", bnCoinDay.ToString().c_str());
    nCoinAge = bnCoinDay.getuint64();
    return true;
}

// ppcoin: total coin age spent in block, in the unit of coin-days.
bool CBlock::GetCoinAge(uint64& nCoinAge) const
{
    nCoinAge = 0;

    CTxDB txdb("r");
    BOOST_FOREACH(const CTransaction& tx, vtx)
    {
        uint64 nTxCoinAge;
        if (tx.GetCoinAge(txdb, nTxCoinAge))
            nCoinAge += nTxCoinAge;
        else
            return false;
    }

    if (nCoinAge == 0) // block coin age minimum 1 coin-day
        nCoinAge = 1;
    if (fDebug && GetBoolArg("-printcoinage"))
        printf("block coin age total nCoinDays=%"PRI64d"\n", nCoinAge);
    return true;
}


bool CBlock::AddToBlockIndex(unsigned int nFile, unsigned int nBlockPos)
{
    // Check for duplicate
    uint256 hash = GetHash();
    if (mapBlockIndex.count(hash))
        return error("AddToBlockIndex() : %s already exists", hash.ToString().substr(0,20).c_str());

    // Construct new block index object
    CBlockIndex* pindexNew = new CBlockIndex(nFile, nBlockPos, *this);
    if (!pindexNew)
        return error("AddToBlockIndex() : new CBlockIndex failed");
    map::iterator mi = mapBlockIndex.insert(make_pair(hash, pindexNew)).first;
    if (pindexNew->fProofOfStake) 
        setStakeSeen.insert(make_pair(pindexNew->prevoutStake, pindexNew->nStakeTime));

    pindexNew->phashBlock = &((*mi).first);
    map::iterator miPrev = mapBlockIndex.find(hashPrevBlock);
    if (miPrev != mapBlockIndex.end())
    {
        pindexNew->pprev = (*miPrev).second;
        pindexNew->nHeight = pindexNew->pprev->nHeight + 1;
    }

    // ppcoin: compute chain trust score
    pindexNew->bnChainTrust = (pindexNew->pprev ? pindexNew->pprev->bnChainTrust : 0) + pindexNew->GetBlockTrust();

    CTxDB txdb;
    if (!txdb.TxnBegin())
        return false;
    txdb.WriteBlockIndex(CDiskBlockIndex(pindexNew));
    if (!txdb.TxnCommit())
        return false;

    // New best
    if (pindexNew->bnChainTrust > bnBestChainTrust)
        if (!SetBestChain(txdb, pindexNew))
            return false;

    txdb.Close();

    if (pindexNew == pindexBest)
    {
        // Notify UI to display prev block's coinbase if it was ours
        static uint256 hashPrevBestCoinBase;
        UpdatedTransaction(hashPrevBestCoinBase);
        hashPrevBestCoinBase = vtx[0].GetHash();
    }

    MainFrameRepaint();
    return true;
}




bool CBlock::CheckBlock() const
{
    // These are checks that are independent of context
    // that can be verified before saving an orphan block.

    // Size limits
    if (vtx.empty() || vtx.size() > MAX_BLOCK_SIZE || ::GetSerializeSize(*this, SER_NETWORK, PROTOCOL_VERSION) > MAX_BLOCK_SIZE)
        return DoS(100, error("CheckBlock() : size limits failed"));

    // Check proof of work matches claimed amount
    if (IsProofOfWork() && !CheckProofOfWork(GetHash(), nBits))
        return DoS(50, error("CheckBlock() : proof of work failed"));

    // Check timestamp
    if (GetBlockTime() > GetAdjustedTime() + nMaxClockDrift)
        return error("CheckBlock() : block timestamp too far in the future");

    // First transaction must be coinbase, the rest must not be
    if (vtx.empty() || !vtx[0].IsCoinBase())
        return DoS(100, error("CheckBlock() : first tx is not coinbase"));
    for (unsigned int i = 1; i < vtx.size(); i++)
        if (vtx[i].IsCoinBase())
            return DoS(100, error("CheckBlock() : more than one coinbase"));

    // ppcoin: only the second transaction can be the optional coinstake
    for (int i = 2; i < vtx.size(); i++)
        if (vtx[i].IsCoinStake())
            return DoS(100, error("CheckBlock() : coinstake in wrong position"));

    // ppcoin: coinbase output should be empty if proof-of-stake block
    if (IsProofOfStake() && (vtx[0].vout.size() != 1 || !vtx[0].vout[0].IsEmpty()))
        return error("CheckBlock() : coinbase output not empty for proof-of-stake block");

    // Check coinbase timestamp
    if (GetBlockTime() > (int64)vtx[0].nTime + nMaxClockDrift)
        return DoS(50, error("CheckBlock() : coinbase timestamp is too early"));

    // Check coinstake timestamp
    if (IsProofOfStake() && GetBlockTime() > (int64)vtx[1].nTime + nMaxClockDrift)
        return DoS(50, error("CheckBlock() : coinstake timestamp is too early"));

    // Check coinbase reward
    if (vtx[0].GetValueOut() > (IsProofOfWork()? (GetProofOfWorkReward(nBits) - vtx[0].GetMinFee() + MIN_TX_FEE) : 0))
        return DoS(50, error("CheckBlock() : coinbase reward exceeded %s > %s", 
                   FormatMoney(vtx[0].GetValueOut()).c_str(),
                   FormatMoney(IsProofOfWork()? GetProofOfWorkReward(nBits) : 0).c_str()));

    // Check transactions
    BOOST_FOREACH(const CTransaction& tx, vtx)
    {
        if (!tx.CheckTransaction())
            return DoS(tx.nDoS, error("CheckBlock() : CheckTransaction failed"));
        // ppcoin: check transaction timestamp
        if (GetBlockTime() < (int64)tx.nTime)
            return DoS(50, error("CheckBlock() : block timestamp earlier than transaction timestamp"));
    }

    // Check for duplicate txids. This is caught by ConnectInputs(),
    // but catching it earlier avoids a potential DoS attack:
    set uniqueTx;
    BOOST_FOREACH(const CTransaction& tx, vtx)
    {
        uniqueTx.insert(tx.GetHash());
    }
    if (uniqueTx.size() != vtx.size())
        return DoS(100, error("CheckBlock() : duplicate transaction"));

    unsigned int nSigOps = 0;
    BOOST_FOREACH(const CTransaction& tx, vtx)
    {
        nSigOps += tx.GetLegacySigOpCount();
    }
    if (nSigOps > MAX_BLOCK_SIGOPS)
        return DoS(100, error("CheckBlock() : out-of-bounds SigOpCount"));

    // Check merkleroot
    if (hashMerkleRoot != BuildMerkleTree())
        return DoS(100, error("CheckBlock() : hashMerkleRoot mismatch"));

    // ppcoin: check block signature
    if (!CheckBlockSignature())
        return DoS(100, error("CheckBlock() : bad block signature"));

    return true;
}

bool CBlock::AcceptBlock()
{
    // Check for duplicate
    uint256 hash = GetHash();
    if (mapBlockIndex.count(hash))
        return error("AcceptBlock() : block already in mapBlockIndex");

    // Get prev block index
    map::iterator mi = mapBlockIndex.find(hashPrevBlock);
    if (mi == mapBlockIndex.end())
        return DoS(10, error("AcceptBlock() : prev block not found"));
    CBlockIndex* pindexPrev = (*mi).second;
    int nHeight = pindexPrev->nHeight+1;

    // Check proof-of-work or proof-of-stake
    if (nBits != GetNextTargetRequired(pindexPrev, IsProofOfStake()))
        return DoS(100, error("AcceptBlock() : incorrect proof-of-work/proof-of-stake"));

    // Check timestamp against prev
    if (GetBlockTime() <= pindexPrev->GetMedianTimePast() || GetBlockTime() + nMaxClockDrift < pindexPrev->GetBlockTime())
        return error("AcceptBlock() : block's timestamp is too early");

    // Check that all transactions are finalized
    BOOST_FOREACH(const CTransaction& tx, vtx)
        if (!tx.IsFinal(nHeight, GetBlockTime()))
            return DoS(10, error("AcceptBlock() : contains a non-final transaction"));

    // Check that the block chain matches the known block chain up to a hardened checkpoint
    if (!Checkpoints::CheckHardened(nHeight, hash))
        return DoS(100, error("AcceptBlock() : rejected by hardened checkpoint lockin at %d", nHeight));

    // ppcoin: check that the block satisfies synchronized checkpoint
    if (!Checkpoints::CheckSync(hash, pindexPrev))
        return error("AcceptBlock() : rejected by synchronized checkpoint");

    // Write block to history file
    if (!CheckDiskSpace(::GetSerializeSize(*this, SER_DISK, CLIENT_VERSION)))
        return error("AcceptBlock() : out of disk space");
    unsigned int nFile = -1;
    unsigned int nBlockPos = 0;
    if (!WriteToDisk(nFile, nBlockPos))
        return error("AcceptBlock() : WriteToDisk failed");
    if (!AddToBlockIndex(nFile, nBlockPos))
        return error("AcceptBlock() : AddToBlockIndex failed");

    // Relay inventory, but don't relay old inventory during initial block download
    int nBlockEstimate = Checkpoints::GetTotalBlocksEstimate();
    if (hashBestChain == hash)
    {
        LOCK(cs_vNodes);
        BOOST_FOREACH(CNode* pnode, vNodes)
            if (nBestHeight > (pnode->nStartingHeight != -1 ? pnode->nStartingHeight - 2000 : nBlockEstimate))
                pnode->PushInventory(CInv(MSG_BLOCK, hash));
    }

    // ppcoin: check pending sync-checkpoint
    Checkpoints::AcceptPendingSyncCheckpoint();

    return true;
}

bool ProcessBlock(CNode* pfrom, CBlock* pblock)
{
    // Check for duplicate
    uint256 hash = pblock->GetHash();
    if (mapBlockIndex.count(hash))
        return error("ProcessBlock() : already have block %d %s", mapBlockIndex[hash]->nHeight, hash.ToString().substr(0,20).c_str());
    if (mapOrphanBlocks.count(hash))
        return error("ProcessBlock() : already have block (orphan) %s", hash.ToString().substr(0,20).c_str());

    // ppcoin: check proof-of-stake
    // Limited duplicity on stake: prevents block flood attack
    // Duplicate stake allowed only when there is orphan child block
    if (pblock->IsProofOfStake() && setStakeSeen.count(pblock->GetProofOfStake()) && !mapOrphanBlocksByPrev.count(hash) && !Checkpoints::WantedByPendingSyncCheckpoint(hash))
        return error("ProcessBlock() : duplicate proof-of-stake (%s, %d) for block %s", pblock->GetProofOfStake().first.ToString().c_str(), pblock->GetProofOfStake().second, hash.ToString().c_str());

    // Preliminary checks
    if (!pblock->CheckBlock())
        return error("ProcessBlock() : CheckBlock FAILED");

    // ppcoin: verify hash target and signature of coinstake tx
    if (pblock->IsProofOfStake() && !pblock->vtx[1].CheckProofOfStake(pblock->nBits))
    {
        printf("WARNING: ProcessBlock(): check proof-of-stake failed for block %s\n", hash.ToString().c_str());
        return false; // do not error here as we expect this during initial block download
    }

    CBlockIndex* pcheckpoint = Checkpoints::GetLastSyncCheckpoint();
    if (pcheckpoint && pblock->hashPrevBlock != hashBestChain && !Checkpoints::WantedByPendingSyncCheckpoint(hash))
    {
        // Extra checks to prevent "fill up memory by spamming with bogus blocks"
        int64 deltaTime = pblock->GetBlockTime() - pcheckpoint->nTime;
        CBigNum bnNewBlock;
        bnNewBlock.SetCompact(pblock->nBits);
        CBigNum bnRequired;
        bnRequired.SetCompact(ComputeMinWork(GetLastBlockIndex(pcheckpoint, pblock->IsProofOfStake())->nBits, deltaTime));

        if (bnNewBlock > bnRequired)
        {
            if (pfrom)
                pfrom->Misbehaving(100);
            return error("ProcessBlock() : block with too little %s", pblock->IsProofOfStake()? "proof-of-stake" : "proof-of-work");
        }
    }

    // ppcoin: ask for pending sync-checkpoint if any
    if (!IsInitialBlockDownload())
        Checkpoints::AskForPendingSyncCheckpoint(pfrom);

    // If don't already have its previous block, shunt it off to holding area until we get it
    if (!mapBlockIndex.count(pblock->hashPrevBlock))
    {
        printf("ProcessBlock: ORPHAN BLOCK, prev=%s\n", pblock->hashPrevBlock.ToString().substr(0,20).c_str());
        CBlock* pblock2 = new CBlock(*pblock);
        // ppcoin: check proof-of-stake
        if (pblock2->IsProofOfStake())
        {
            // Limited duplicity on stake: prevents block flood attack
            // Duplicate stake allowed only when there is orphan child block
            if (setStakeSeenOrphan.count(pblock2->GetProofOfStake()) && !mapOrphanBlocksByPrev.count(hash) && !Checkpoints::WantedByPendingSyncCheckpoint(hash))
                return error("ProcessBlock() : duplicate proof-of-stake (%s, %d) for orphan block %s", pblock2->GetProofOfStake().first.ToString().c_str(), pblock2->GetProofOfStake().second, hash.ToString().c_str());
            else
                setStakeSeenOrphan.insert(pblock2->GetProofOfStake());
        }
        mapOrphanBlocks.insert(make_pair(hash, pblock2));
        mapOrphanBlocksByPrev.insert(make_pair(pblock2->hashPrevBlock, pblock2));

        // Ask this guy to fill in what we're missing
        if (pfrom)
        {
            pfrom->PushGetBlocks(pindexBest, GetOrphanRoot(pblock2));
            // ppcoin: getblocks may not obtain the ancestor block rejected
            // earlier by duplicate-stake check so we ask for it again directly
            if (!IsInitialBlockDownload())
                pfrom->AskFor(CInv(MSG_BLOCK, WantedByOrphan(pblock2)));
        }
        return true;
    }

    // Store to disk
    if (!pblock->AcceptBlock())
        return error("ProcessBlock() : AcceptBlock FAILED");

    // Recursively process any orphan blocks that depended on this one
    vector vWorkQueue;
    vWorkQueue.push_back(hash);
    for (unsigned int i = 0; i < vWorkQueue.size(); i++)
    {
        uint256 hashPrev = vWorkQueue[i];
        for (multimap::iterator mi = mapOrphanBlocksByPrev.lower_bound(hashPrev);
             mi != mapOrphanBlocksByPrev.upper_bound(hashPrev);
             ++mi)
        {
            CBlock* pblockOrphan = (*mi).second;
            if (pblockOrphan->AcceptBlock())
                vWorkQueue.push_back(pblockOrphan->GetHash());
            mapOrphanBlocks.erase(pblockOrphan->GetHash());
            setStakeSeenOrphan.erase(pblockOrphan->GetProofOfStake());
            delete pblockOrphan;
        }
        mapOrphanBlocksByPrev.erase(hashPrev);
    }

    printf("ProcessBlock: ACCEPTED\n");

    // ppcoin: if responsible for sync-checkpoint send it
    if (pfrom && !CSyncCheckpoint::strMasterPrivKey.empty())
        Checkpoints::SendSyncCheckpoint(Checkpoints::AutoSelectSyncCheckpoint());

    return true;
}

// ppcoin: sign block
bool CBlock::SignBlock(const CKeyStore& keystore)
{
    vector vSolutions;
    txnouttype whichType;
    const CTxOut& txout = IsProofOfStake()? vtx[1].vout[1] : vtx[0].vout[0];

    if (!Solver(txout.scriptPubKey, whichType, vSolutions))
        return false;
    if (whichType == TX_PUBKEY)
    {
        // Sign
        const valtype& vchPubKey = vSolutions[0];
        CKey key;
        if (!keystore.GetKey(Hash160(vchPubKey), key))
            return false;
        if (key.GetPubKey() != vchPubKey)
            return false;
        return key.Sign(GetHash(), vchBlockSig);
    }
    return false;
}

// ppcoin: check block signature
bool CBlock::CheckBlockSignature() const
{
    if (GetHash() == hashGenesisBlock)
        return vchBlockSig.empty();

    vector vSolutions;
    txnouttype whichType;
    const CTxOut& txout = IsProofOfStake()? vtx[1].vout[1] : vtx[0].vout[0];

    if (!Solver(txout.scriptPubKey, whichType, vSolutions))
        return false;
    if (whichType == TX_PUBKEY)
    {
        const valtype& vchPubKey = vSolutions[0];
        CKey key;
        if (!key.SetPubKey(vchPubKey))
            return false;
        if (vchBlockSig.empty())
            return false;
        return key.Verify(GetHash(), vchBlockSig);
    }
    return false;
}

// CreateNewBlock:
//   fProofOfStake: try (best effort) to make a proof-of-stake block
CBlock* CreateNewBlock(CWallet* pwallet, bool fProofOfStake)
{
    CReserveKey reservekey(pwallet);

    // Create new block
    auto_ptr pblock(new CBlock());
    if (!pblock.get())
        return NULL;

    // Create coinbase tx
    CTransaction txNew;
    txNew.vin.resize(1);
    txNew.vin[0].prevout.SetNull();
    txNew.vout.resize(1);
    txNew.vout[0].scriptPubKey << reservekey.GetReservedKey() << OP_CHECKSIG;

    // Add our coinbase tx as first transaction
    pblock->vtx.push_back(txNew);

    // ppcoin: if coinstake available add coinstake tx
    static int64 nLastCoinStakeSearchTime = GetAdjustedTime();  // only initialized at startup
    CBlockIndex* pindexPrev = pindexBest;

    if (fProofOfStake)  // attemp to find a coinstake
    {
        pblock->nBits = GetNextTargetRequired(pindexPrev, true);
        CTransaction txCoinStake;
        int64 nSearchTime = GetAdjustedTime();
        if (nSearchTime > nLastCoinStakeSearchTime)
        {
            if (pwallet->CreateCoinStake(*pwallet, pblock->nBits, nSearchTime-nLastCoinStakeSearchTime, txCoinStake))
            {
                pblock->vtx.push_back(txCoinStake);
                pblock->vtx[0].vout[0].SetEmpty();
            }
            nLastCoinStakeSearchInterval = nSearchTime - nLastCoinStakeSearchTime;
            nLastCoinStakeSearchTime = nSearchTime;
        }
    }

    pblock->nBits = GetNextTargetRequired(pindexPrev, pblock->IsProofOfStake());

    // Collect memory pool transactions into the block
    int64 nFees = 0;
    {
        LOCK2(cs_main, mempool.cs);
        CTxDB txdb("r");

        // Priority order to process transactions
        list vOrphan; // list memory doesn't move
        map > mapDependers;
        multimap mapPriority;
        for (map::iterator mi = mempool.mapTx.begin(); mi != mempool.mapTx.end(); ++mi)
        {
            CTransaction& tx = (*mi).second;
            if (tx.IsCoinBase() || tx.IsCoinStake() || !tx.IsFinal())
                continue;

            COrphan* porphan = NULL;
            double dPriority = 0;
            BOOST_FOREACH(const CTxIn& txin, tx.vin)
            {
                // Read prev transaction
                CTransaction txPrev;
                CTxIndex txindex;
                if (!txPrev.ReadFromDisk(txdb, txin.prevout, txindex))
                {
                    // Has to wait for dependencies
                    if (!porphan)
                    {
                        // Use list for automatic deletion
                        vOrphan.push_back(COrphan(&tx));
                        porphan = &vOrphan.back();
                    }
                    mapDependers[txin.prevout.hash].push_back(porphan);
                    porphan->setDependsOn.insert(txin.prevout.hash);
                    continue;
                }
                int64 nValueIn = txPrev.vout[txin.prevout.n].nValue;

                // Read block header
                int nConf = txindex.GetDepthInMainChain();

                dPriority += (double)nValueIn * nConf;

                if (fDebug && GetBoolArg("-printpriority"))
                    printf("priority     nValueIn=%-12"PRI64d" nConf=%-5d dPriority=%-20.1f\n", nValueIn, nConf, dPriority);
            }

            // Priority is sum(valuein * age) / txsize
            dPriority /= ::GetSerializeSize(tx, SER_NETWORK, PROTOCOL_VERSION);

            if (porphan)
                porphan->dPriority = dPriority;
            else
                mapPriority.insert(make_pair(-dPriority, &(*mi).second));

            if (fDebug && GetBoolArg("-printpriority"))
            {
                printf("priority %-20.1f %s\n%s", dPriority, tx.GetHash().ToString().substr(0,10).c_str(), tx.ToString().c_str());
                if (porphan)
                    porphan->print();
                printf("\n");
            }
        }

        // Collect transactions into block
        map mapTestPool;
        uint64 nBlockSize = 1000;
        uint64 nBlockTx = 0;
        int nBlockSigOps = 100;
        while (!mapPriority.empty())
        {
            // Take highest priority transaction off priority queue
            CTransaction& tx = *(*mapPriority.begin()).second;
            mapPriority.erase(mapPriority.begin());

            // Size limits
            unsigned int nTxSize = ::GetSerializeSize(tx, SER_NETWORK, PROTOCOL_VERSION);
            if (nBlockSize + nTxSize >= MAX_BLOCK_SIZE_GEN)
                continue;

            // Legacy limits on sigOps:
            unsigned int nTxSigOps = tx.GetLegacySigOpCount();
            if (nBlockSigOps + nTxSigOps >= MAX_BLOCK_SIGOPS)
                continue;

            // Timestamp limit
            if (tx.nTime > GetAdjustedTime())
                continue;

            // ppcoin: simplify transaction fee - allow free = false
            int64 nMinFee = tx.GetMinFee(nBlockSize, false, GMF_BLOCK);

            // Connecting shouldn't fail due to dependency on other memory pool transactions
            // because we're already processing them in order of dependency
            map mapTestPoolTmp(mapTestPool);
            MapPrevTx mapInputs;
            bool fInvalid;
            if (!tx.FetchInputs(txdb, mapTestPoolTmp, false, true, mapInputs, fInvalid))
                continue;

            int64 nTxFees = tx.GetValueIn(mapInputs)-tx.GetValueOut();
            if (nTxFees < nMinFee)
                continue;

            nTxSigOps += tx.GetP2SHSigOpCount(mapInputs);
            if (nBlockSigOps + nTxSigOps >= MAX_BLOCK_SIGOPS)
                continue;

            if (!tx.ConnectInputs(txdb, mapInputs, mapTestPoolTmp, CDiskTxPos(1,1,1), pindexPrev, false, true))
                continue;
            mapTestPoolTmp[tx.GetHash()] = CTxIndex(CDiskTxPos(1,1,1), tx.vout.size());
            swap(mapTestPool, mapTestPoolTmp);

            // Added
            pblock->vtx.push_back(tx);
            nBlockSize += nTxSize;
            ++nBlockTx;
            nBlockSigOps += nTxSigOps;
            nFees += nTxFees;

            // Add transactions that depend on this one to the priority queue
            uint256 hash = tx.GetHash();
            if (mapDependers.count(hash))
            {
                BOOST_FOREACH(COrphan* porphan, mapDependers[hash])
                {
                    if (!porphan->setDependsOn.empty())
                    {
                        porphan->setDependsOn.erase(hash);
                        if (porphan->setDependsOn.empty())
                            mapPriority.insert(make_pair(-porphan->dPriority, porphan->ptx));
                    }
                }
            }
        }

        nLastBlockTx = nBlockTx;
        nLastBlockSize = nBlockSize;
        if (fDebug && GetBoolArg("-printpriority"))
            printf("CreateNewBlock(): total size %lu\n", nBlockSize);

    }
    if (pblock->IsProofOfWork())
        pblock->vtx[0].vout[0].nValue = GetProofOfWorkReward(pblock->nBits);

    // Fill in header
    pblock->hashPrevBlock  = pindexPrev->GetBlockHash();
    pblock->hashMerkleRoot = pblock->BuildMerkleTree();
    pblock->nTime          = max(pindexPrev->GetMedianTimePast()+1, pblock->GetMaxTransactionTime());
    pblock->nTime          = max(pblock->GetBlockTime(), pindexPrev->GetBlockTime() - nMaxClockDrift);
    pblock->UpdateTime(pindexPrev);
    pblock->nNonce         = 0;

    return pblock.release();
}


void IncrementExtraNonce(CBlock* pblock, CBlockIndex* pindexPrev, unsigned int& nExtraNonce)
{
    // Update nExtraNonce
    static uint256 hashPrevBlock;
    if (hashPrevBlock != pblock->hashPrevBlock)
    {
        nExtraNonce = 0;
        hashPrevBlock = pblock->hashPrevBlock;
    }
    ++nExtraNonce;
    pblock->vtx[0].vin[0].scriptSig = (CScript() << pblock->nTime << CBigNum(nExtraNonce)) + COINBASE_FLAGS;
    assert(pblock->vtx[0].vin[0].scriptSig.size() <= 100);

    pblock->hashMerkleRoot = pblock->BuildMerkleTree();
}

void BitcoinMiner(CWallet *pwallet, bool fProofOfStake)
{
    printf("CPUMiner started for proof-of-%s\n", fProofOfStake? "stake" : "work");
    SetThreadPriority(THREAD_PRIORITY_LOWEST);

    // Each thread has its own key and counter
    CReserveKey reservekey(pwallet);
    unsigned int nExtraNonce = 0;

    while (fGenerateBitcoins || fProofOfStake)
    {
        if (fShutdown)
            return;
        while (vNodes.empty() || IsInitialBlockDownload())
        {
            Sleep(1000);
            if (fShutdown)
                return;
            if ((!fGenerateBitcoins) && !fProofOfStake)
                return;
        }

        while (pwallet->IsLocked())
        {
            strMintWarning = strMintMessage;
            Sleep(1000);
        }
        strMintWarning = "";

        //
        // Create new block
        //
        unsigned int nTransactionsUpdatedLast = nTransactionsUpdated;
        CBlockIndex* pindexPrev = pindexBest;

        auto_ptr pblock(CreateNewBlock(pwallet, fProofOfStake));
        if (!pblock.get())
            return;

        IncrementExtraNonce(pblock.get(), pindexPrev, nExtraNonce);

        if (fProofOfStake)
        {
            // ppcoin: if proof-of-stake block found then process block
            if (pblock->IsProofOfStake())
            {
                if (!pblock->SignBlock(*pwalletMain))
                {
                    strMintWarning = strMintMessage;
                    continue;
                }
                strMintWarning = "";
                printf("CPUMiner : proof-of-stake block found %s\n", pblock->GetHash().ToString().c_str()); 
                SetThreadPriority(THREAD_PRIORITY_NORMAL);
                CheckWork(pblock.get(), *pwalletMain, reservekey);
                SetThreadPriority(THREAD_PRIORITY_LOWEST);
            }
            Sleep(500);
            continue;
        }

        printf("Running BitcoinMiner with %d transactions in block\n", pblock->vtx.size());


        //
        // Prebuild hash buffers
        //
        char pmidstatebuf[32+16]; char* pmidstate = alignup<16>(pmidstatebuf);
        char pdatabuf[128+16];    char* pdata     = alignup<16>(pdatabuf);
        char phash1buf[64+16];    char* phash1    = alignup<16>(phash1buf);

        FormatHashBuffers(pblock.get(), pmidstate, pdata, phash1);

        unsigned int& nBlockTime = *(unsigned int*)(pdata + 64 + 4);
        unsigned int& nBlockNonce = *(unsigned int*)(pdata + 64 + 12);


        //
        // Search
        //
        int64 nStart = GetTime();
        uint256 hashTarget = CBigNum().SetCompact(pblock->nBits).getuint256();
        uint256 hashbuf[2];
        uint256& hash = *alignup<16>(hashbuf);
        loop
        {
            unsigned int nHashesDone = 0;
            unsigned int nNonceFound;

            // Crypto++ SHA-256
            nNonceFound = ScanHash_CryptoPP(pmidstate, pdata + 64, phash1,
                                            (char*)&hash, nHashesDone);

            // Check if something found
            if (nNonceFound != (unsigned int) -1)
            {
                for (unsigned int i = 0; i < sizeof(hash)/4; i++)
                    ((unsigned int*)&hash)[i] = ByteReverse(((unsigned int*)&hash)[i]);

                if (hash <= hashTarget)
                {
                    // Found a solution
                    pblock->nNonce = ByteReverse(nNonceFound);
                    assert(hash == pblock->GetHash());
                    if (!pblock->SignBlock(*pwalletMain))
                    {
                        strMintWarning = strMintMessage;
                        break;
                    }
                    strMintWarning = "";
                    SetThreadPriority(THREAD_PRIORITY_NORMAL);
                    CheckWork(pblock.get(), *pwalletMain, reservekey);
                    SetThreadPriority(THREAD_PRIORITY_LOWEST);
                    break;
                }
            }

            // Meter hashes/sec
            static int64 nHashCounter;
            if (nHPSTimerStart == 0)
            {
                nHPSTimerStart = GetTimeMillis();
                nHashCounter = 0;
            }
            else
                nHashCounter += nHashesDone;
            if (GetTimeMillis() - nHPSTimerStart > 4000)
            {
                static CCriticalSection cs;
                {
                    LOCK(cs);
                    if (GetTimeMillis() - nHPSTimerStart > 4000)
                    {
                        dHashesPerSec = 1000.0 * nHashCounter / (GetTimeMillis() - nHPSTimerStart);
                        nHPSTimerStart = GetTimeMillis();
                        nHashCounter = 0;
                        static int64 nLogTime;
                        if (GetTime() - nLogTime > 30 * 60)
                        {
                            nLogTime = GetTime();
                            printf("%s ", DateTimeStrFormat(GetTime()).c_str());
                            printf("hashmeter %3d CPUs %6.0f khash/s\n", vnThreadsRunning[THREAD_MINER], dHashesPerSec/1000.0);
                        }
                    }
                }
            }

            // Check for stop or if block needs to be rebuilt
            if (fShutdown)
                return;
            if (!fGenerateBitcoins)
                return;
            if (fLimitProcessors && vnThreadsRunning[THREAD_MINER] > nLimitProcessors)
                return;
            if (vNodes.empty())
                break;
            if (nBlockNonce >= 0xffff0000)
                break;
            if (nTransactionsUpdated != nTransactionsUpdatedLast && GetTime() - nStart > 60)
                break;
            if (pindexPrev != pindexBest)
                break;

            // Update nTime every few seconds
            pblock->nTime = max(pindexPrev->GetMedianTimePast()+1, pblock->GetMaxTransactionTime());
            pblock->nTime = max(pblock->GetBlockTime(), pindexPrev->GetBlockTime() - nMaxClockDrift);
            pblock->UpdateTime(pindexPrev);
            nBlockTime = ByteReverse(pblock->nTime);
            if (pblock->GetBlockTime() >= (int64)pblock->vtx[0].nTime + nMaxClockDrift)
                break;  // need to update coinbase timestamp
        }
    }
}