--- /dev/null
+// Copyright (c) 2012-2013 The PPCoin developers
+// Distributed under the MIT/X11 software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <boost/assign/list_of.hpp>
+
+#include "kernel.h"
+#include "db.h"
+
+using namespace std;
+
+// Modifier interval: time to elapse before new modifier is computed
+// Set to 6-hour for production network and 20-minute for test network
+unsigned int nModifierInterval = MODIFIER_INTERVAL;
+
+// Hard checkpoints of stake modifiers to ensure they are deterministic
+static std::map<int, unsigned int> mapStakeModifierCheckpoints =
+ boost::assign::map_list_of
+ ( 0, 0x0e00670bu )
+ ( 6000, 0xb7cbc5d3u )
+ ;
+
+// Get the last stake modifier and its generation time from a given block
+static bool GetLastStakeModifier(const CBlockIndex* pindex, uint64& nStakeModifier, int64& nModifierTime)
+{
+ if (!pindex)
+ return error("GetLastStakeModifier: null pindex");
+ while (pindex && pindex->pprev && !pindex->GeneratedStakeModifier())
+ pindex = pindex->pprev;
+ if (!pindex->GeneratedStakeModifier())
+ return error("GetLastStakeModifier: no generation at genesis block");
+ nStakeModifier = pindex->nStakeModifier;
+ nModifierTime = pindex->GetBlockTime();
+ return true;
+}
+
+// Get selection interval section (in seconds)
+static int64 GetStakeModifierSelectionIntervalSection(int nSection)
+{
+ assert (nSection >= 0 && nSection < 64);
+ return (nModifierInterval * 63 / (63 + ((63 - nSection) * (MODIFIER_INTERVAL_RATIO - 1))));
+}
+
+// Get stake modifier selection interval (in seconds)
+static int64 GetStakeModifierSelectionInterval()
+{
+ int64 nSelectionInterval = 0;
+ for (int nSection=0; nSection<64; nSection++)
+ nSelectionInterval += GetStakeModifierSelectionIntervalSection(nSection);
+ return nSelectionInterval;
+}
+
+// select a block from the candidate blocks in vSortedByTimestamp, excluding
+// already selected blocks in vSelectedBlocks, and with timestamp up to
+// nSelectionIntervalStop.
+static bool SelectBlockFromCandidates(
+ vector<pair<int64, uint256> >& vSortedByTimestamp,
+ map<uint256, const CBlockIndex*>& mapSelectedBlocks,
+ int64 nSelectionIntervalStop, uint64 nStakeModifierPrev,
+ const CBlockIndex** pindexSelected)
+{
+ bool fSelected = false;
+ uint256 hashBest = 0;
+ *pindexSelected = (const CBlockIndex*) 0;
+ BOOST_FOREACH(const PAIRTYPE(int64, uint256)& item, vSortedByTimestamp)
+ {
+ if (!mapBlockIndex.count(item.second))
+ return error("SelectBlockFromCandidates: failed to find block index for candidate block %s", item.second.ToString().c_str());
+ const CBlockIndex* pindex = mapBlockIndex[item.second];
+ if (fSelected && pindex->GetBlockTime() > nSelectionIntervalStop)
+ break;
+ if (mapSelectedBlocks.count(pindex->GetBlockHash()) > 0)
+ continue;
+ // compute the selection hash by hashing its proof-hash and the
+ // previous proof-of-stake modifier
+ uint256 hashProof = pindex->IsProofOfStake()? pindex->hashProofOfStake : pindex->GetBlockHash();
+ CDataStream ss(SER_GETHASH, 0);
+ ss << hashProof << nStakeModifierPrev;
+ uint256 hashSelection = Hash(ss.begin(), ss.end());
+ // the selection hash is divided by 2**32 so that proof-of-stake block
+ // is always favored over proof-of-work block. this is to preserve
+ // the energy efficiency property
+ if (pindex->IsProofOfStake())
+ hashSelection >>= 32;
+ if (fSelected && hashSelection < hashBest)
+ {
+ hashBest = hashSelection;
+ *pindexSelected = (const CBlockIndex*) pindex;
+ }
+ else if (!fSelected)
+ {
+ fSelected = true;
+ hashBest = hashSelection;
+ *pindexSelected = (const CBlockIndex*) pindex;
+ }
+ }
+ if (fDebug && GetBoolArg("-printstakemodifier"))
+ printf("SelectBlockFromCandidates: selection hash=%s\n", hashBest.ToString().c_str());
+ return fSelected;
+}
+
+// Stake Modifier (hash modifier of proof-of-stake):
+// The purpose of stake modifier is to prevent a txout (coin) owner from
+// computing future proof-of-stake generated by this txout at the time
+// of transaction confirmation. To meet kernel protocol, the txout
+// must hash with a future stake modifier to generate the proof.
+// Stake modifier consists of bits each of which is contributed from a
+// selected block of a given block group in the past.
+// The selection of a block is based on a hash of the block's proof-hash and
+// the previous stake modifier.
+// Stake modifier is recomputed at a fixed time interval instead of every
+// block. This is to make it difficult for an attacker to gain control of
+// additional bits in the stake modifier, even after generating a chain of
+// blocks.
+bool ComputeNextStakeModifier(const CBlockIndex* pindexPrev, uint64& nStakeModifier, bool& fGeneratedStakeModifier)
+{
+ nStakeModifier = 0;
+ fGeneratedStakeModifier = false;
+ if (!pindexPrev)
+ {
+ fGeneratedStakeModifier = true;
+ return true; // genesis block's modifier is 0
+ }
+ // First find current stake modifier and its generation block time
+ // if it's not old enough, return the same stake modifier
+ int64 nModifierTime = 0;
+ if (!GetLastStakeModifier(pindexPrev, nStakeModifier, nModifierTime))
+ return error("ComputeNextStakeModifier: unable to get last modifier");
+ if (fDebug)
+ {
+ printf("ComputeNextStakeModifier: prev modifier=0x%016"PRI64x" time=%s\n", nStakeModifier, DateTimeStrFormat(nModifierTime).c_str());
+ }
+ if (nModifierTime / nModifierInterval >= pindexPrev->GetBlockTime() / nModifierInterval)
+ return true;
+
+ // Sort candidate blocks by timestamp
+ vector<pair<int64, uint256> > vSortedByTimestamp;
+ vSortedByTimestamp.reserve(64 * nModifierInterval / STAKE_TARGET_SPACING);
+ int64 nSelectionInterval = GetStakeModifierSelectionInterval();
+ int64 nSelectionIntervalStart = (pindexPrev->GetBlockTime() / nModifierInterval) * nModifierInterval - nSelectionInterval;
+ const CBlockIndex* pindex = pindexPrev;
+ while (pindex && pindex->GetBlockTime() >= nSelectionIntervalStart)
+ {
+ vSortedByTimestamp.push_back(make_pair(pindex->GetBlockTime(), pindex->GetBlockHash()));
+ pindex = pindex->pprev;
+ }
+ int nHeightFirstCandidate = pindex ? (pindex->nHeight + 1) : 0;
+ reverse(vSortedByTimestamp.begin(), vSortedByTimestamp.end());
+ sort(vSortedByTimestamp.begin(), vSortedByTimestamp.end());
+
+ // Select 64 blocks from candidate blocks to generate stake modifier
+ uint64 nStakeModifierNew = 0;
+ int64 nSelectionIntervalStop = nSelectionIntervalStart;
+ map<uint256, const CBlockIndex*> mapSelectedBlocks;
+ for (int nRound=0; nRound<min(64, (int)vSortedByTimestamp.size()); nRound++)
+ {
+ // add an interval section to the current selection round
+ nSelectionIntervalStop += GetStakeModifierSelectionIntervalSection(nRound);
+ // select a block from the candidates of current round
+ if (!SelectBlockFromCandidates(vSortedByTimestamp, mapSelectedBlocks, nSelectionIntervalStop, nStakeModifier, &pindex))
+ return error("ComputeNextStakeModifier: unable to select block at round %d", nRound);
+ // write the entropy bit of the selected block
+ nStakeModifierNew |= (((uint64)pindex->GetStakeEntropyBit()) << nRound);
+ // add the selected block from candidates to selected list
+ mapSelectedBlocks.insert(make_pair(pindex->GetBlockHash(), pindex));
+ if (fDebug && GetBoolArg("-printstakemodifier"))
+ printf("ComputeNextStakeModifier: selected round %d stop=%s height=%d bit=%d\n",
+ nRound, DateTimeStrFormat(nSelectionIntervalStop).c_str(), pindex->nHeight, pindex->GetStakeEntropyBit());
+ }
+
+ // Print selection map for visualization of the selected blocks
+ if (fDebug && GetBoolArg("-printstakemodifier"))
+ {
+ string strSelectionMap = "";
+ // '-' indicates proof-of-work blocks not selected
+ strSelectionMap.insert(0, pindexPrev->nHeight - nHeightFirstCandidate + 1, '-');
+ pindex = pindexPrev;
+ while (pindex && pindex->nHeight >= nHeightFirstCandidate)
+ {
+ // '=' indicates proof-of-stake blocks not selected
+ if (pindex->IsProofOfStake())
+ strSelectionMap.replace(pindex->nHeight - nHeightFirstCandidate, 1, "=");
+ pindex = pindex->pprev;
+ }
+ BOOST_FOREACH(const PAIRTYPE(uint256, const CBlockIndex*)& item, mapSelectedBlocks)
+ {
+ // 'S' indicates selected proof-of-stake blocks
+ // 'W' indicates selected proof-of-work blocks
+ strSelectionMap.replace(item.second->nHeight - nHeightFirstCandidate, 1, item.second->IsProofOfStake()? "S" : "W");
+ }
+ printf("ComputeNextStakeModifier: selection height [%d, %d] map %s\n", nHeightFirstCandidate, pindexPrev->nHeight, strSelectionMap.c_str());
+ }
+ if (fDebug)
+ {
+ printf("ComputeNextStakeModifier: new modifier=0x%016"PRI64x" time=%s\n", nStakeModifierNew, DateTimeStrFormat(pindexPrev->GetBlockTime()).c_str());
+ }
+
+ nStakeModifier = nStakeModifierNew;
+ fGeneratedStakeModifier = true;
+ return true;
+}
+
+// The stake modifier used to hash for a stake kernel is chosen as the stake
+// modifier about a selection interval later than the coin generating the kernel
+static bool GetKernelStakeModifier(uint256 hashBlockFrom, uint64& nStakeModifier, int& nStakeModifierHeight, int64& nStakeModifierTime, bool fPrintProofOfStake)
+{
+ nStakeModifier = 0;
+ if (!mapBlockIndex.count(hashBlockFrom))
+ return error("GetKernelStakeModifier() : block not indexed");
+ const CBlockIndex* pindexFrom = mapBlockIndex[hashBlockFrom];
+ nStakeModifierHeight = pindexFrom->nHeight;
+ nStakeModifierTime = pindexFrom->GetBlockTime();
+ int64 nStakeModifierSelectionInterval = GetStakeModifierSelectionInterval();
+ const CBlockIndex* pindex = pindexFrom;
+ // loop to find the stake modifier later by a selection interval
+ while (nStakeModifierTime < pindexFrom->GetBlockTime() + nStakeModifierSelectionInterval)
+ {
+ if (!pindex->pnext)
+ { // reached best block; may happen if node is behind on block chain
+ if (fPrintProofOfStake || (pindex->GetBlockTime() + nStakeMinAge - nStakeModifierSelectionInterval > GetAdjustedTime()))
+ return error("GetKernelStakeModifier() : reached best block %s at height %d from block %s",
+ pindex->GetBlockHash().ToString().c_str(), pindex->nHeight, hashBlockFrom.ToString().c_str());
+ else
+ return false;
+ }
+ pindex = pindex->pnext;
+ if (pindex->GeneratedStakeModifier())
+ {
+ nStakeModifierHeight = pindex->nHeight;
+ nStakeModifierTime = pindex->GetBlockTime();
+ }
+ }
+ nStakeModifier = pindex->nStakeModifier;
+ return true;
+}
+
+// ppcoin kernel protocol
+// coinstake must meet hash target according to the protocol:
+// kernel (input 0) must meet the formula
+// hash(nStakeModifier + txPrev.block.nTime + txPrev.offset + txPrev.nTime + txPrev.vout.n + nTime) < bnTarget * nCoinDayWeight
+// 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:
+// nStakeModifier:
+// (v0.3) scrambles computation to make it very difficult to precompute
+// future proof-of-stake at the time of the coin's confirmation
+// (v0.2) nBits (deprecated): encodes all past block timestamps
+// 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 CheckStakeKernelHash(unsigned int nBits, const CBlock& blockFrom, unsigned int nTxPrevOffset, const CTransaction& txPrev, const COutPoint& prevout, unsigned int nTimeTx, uint256& hashProofOfStake, bool fPrintProofOfStake)
+{
+ if (nTimeTx < txPrev.nTime) // Transaction timestamp violation
+ return error("CheckStakeKernelHash() : nTime violation");
+
+ unsigned int nTimeBlockFrom = blockFrom.GetBlockTime();
+ if (nTimeBlockFrom + nStakeMinAge > nTimeTx) // Min age requirement
+ return error("CheckStakeKernelHash() : min age violation");
+
+ CBigNum bnTargetPerCoinDay;
+ bnTargetPerCoinDay.SetCompact(nBits);
+ int64 nValueIn = txPrev.vout[prevout.n].nValue;
+
+ // v0.3 protocol kernel hash weight starts from 0 at the 30-day min age
+ // this change increases active coins participating the hash and helps
+ // to secure the network when proof-of-stake difficulty is low
+ int64 nTimeWeight = min((int64)nTimeTx - txPrev.nTime, (int64)STAKE_MAX_AGE) - nStakeMinAge;
+ CBigNum bnCoinDayWeight = CBigNum(nValueIn) * nTimeWeight / COIN / (24 * 60 * 60);
+
+ // Calculate hash
+ CDataStream ss(SER_GETHASH, 0);
+ uint64 nStakeModifier = 0;
+ int nStakeModifierHeight = 0;
+ int64 nStakeModifierTime = 0;
+
+ if (!GetKernelStakeModifier(blockFrom.GetHash(), nStakeModifier, nStakeModifierHeight, nStakeModifierTime, fPrintProofOfStake))
+ return false;
+ ss << nStakeModifier;
+
+ ss << nTimeBlockFrom << nTxPrevOffset << txPrev.nTime << prevout.n << nTimeTx;
+ hashProofOfStake = Hash(ss.begin(), ss.end());
+ if (fPrintProofOfStake)
+ {
+ printf("CheckStakeKernelHash() : using modifier 0x%016"PRI64x" at height=%d timestamp=%s for block from height=%d timestamp=%s\n",
+ nStakeModifier, nStakeModifierHeight,
+ DateTimeStrFormat(nStakeModifierTime).c_str(),
+ mapBlockIndex[blockFrom.GetHash()]->nHeight,
+ DateTimeStrFormat(blockFrom.GetBlockTime()).c_str());
+ printf("CheckStakeKernelHash() : check protocol=%s modifier=0x%016"PRI64x" nTimeBlockFrom=%u nTxPrevOffset=%u nTimeTxPrev=%u nPrevout=%u nTimeTx=%u hashProof=%s\n",
+ "0.3",
+ nStakeModifier,
+ nTimeBlockFrom, nTxPrevOffset, txPrev.nTime, prevout.n, nTimeTx,
+ hashProofOfStake.ToString().c_str());
+ }
+
+ // Now check if proof-of-stake hash meets target protocol
+ if (CBigNum(hashProofOfStake) > bnCoinDayWeight * bnTargetPerCoinDay)
+ return false;
+ if (fDebug && !fPrintProofOfStake)
+ {
+ printf("CheckStakeKernelHash() : using modifier 0x%016"PRI64x" at height=%d timestamp=%s for block from height=%d timestamp=%s\n",
+ nStakeModifier, nStakeModifierHeight,
+ DateTimeStrFormat(nStakeModifierTime).c_str(),
+ mapBlockIndex[blockFrom.GetHash()]->nHeight,
+ DateTimeStrFormat(blockFrom.GetBlockTime()).c_str());
+ printf("CheckStakeKernelHash() : pass protocol=%s modifier=0x%016"PRI64x" nTimeBlockFrom=%u nTxPrevOffset=%u nTimeTxPrev=%u nPrevout=%u nTimeTx=%u hashProof=%s\n",
+ "0.3",
+ nStakeModifier,
+ nTimeBlockFrom, nTxPrevOffset, txPrev.nTime, prevout.n, nTimeTx,
+ hashProofOfStake.ToString().c_str());
+ }
+ return true;
+}
+
+// Check kernel hash target and coinstake signature
+bool CheckProofOfStake(const CTransaction& tx, unsigned int nBits, uint256& hashProofOfStake)
+{
+ if (!tx.IsCoinStake())
+ return error("CheckProofOfStake() : called on non-coinstake %s", tx.GetHash().ToString().c_str());
+
+ // Kernel (input 0) must match the stake hash target per coin age (nBits)
+ const CTxIn& txin = tx.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 tx.DoS(1, error("CheckProofOfStake() : INFO: read txPrev failed")); // previous transaction not in main chain, may occur during initial download
+ txdb.Close();
+
+ // Verify signature
+ if (!VerifySignature(txPrev, tx, 0, true, 0))
+ return tx.DoS(100, error("CheckProofOfStake() : VerifySignature failed on coinstake %s", tx.GetHash().ToString().c_str()));
+
+ // Read block header
+ CBlock block;
+ if (!block.ReadFromDisk(txindex.pos.nFile, txindex.pos.nBlockPos, false))
+ return fDebug? error("CheckProofOfStake() : read block failed") : false; // unable to read block of previous transaction
+
+ if (!CheckStakeKernelHash(nBits, block, txindex.pos.nTxPos - txindex.pos.nBlockPos, txPrev, txin.prevout, tx.nTime, hashProofOfStake, fDebug))
+ return tx.DoS(1, error("CheckProofOfStake() : INFO: check kernel failed on coinstake %s, hashProof=%s", tx.GetHash().ToString().c_str(), hashProofOfStake.ToString().c_str())); // may occur during initial download or if behind on block chain sync
+
+ return true;
+}
+
+// Check whether the coinstake timestamp meets protocol
+bool CheckCoinStakeTimestamp(int64 nTimeBlock, int64 nTimeTx)
+{
+ // v0.3 protocol
+ return (nTimeBlock == nTimeTx);
+}
+
+// Get stake modifier checksum
+unsigned int GetStakeModifierChecksum(const CBlockIndex* pindex)
+{
+ assert (pindex->pprev || pindex->GetBlockHash() == hashGenesisBlock);
+ // Hash previous checksum with flags, hashProofOfStake and nStakeModifier
+ CDataStream ss(SER_GETHASH, 0);
+ if (pindex->pprev)
+ ss << pindex->pprev->nStakeModifierChecksum;
+ ss << pindex->nFlags << pindex->hashProofOfStake << pindex->nStakeModifier;
+ uint256 hashChecksum = Hash(ss.begin(), ss.end());
+ hashChecksum >>= (256 - 32);
+ return hashChecksum.Get64();
+}
+
+// Check stake modifier hard checkpoints
+bool CheckStakeModifierCheckpoints(int nHeight, unsigned int nStakeModifierChecksum)
+{
+ if (fTestNet) return true; // Testnet has no checkpoints
+ if (mapStakeModifierCheckpoints.count(nHeight))
+ return nStakeModifierChecksum == mapStakeModifierCheckpoints[nHeight];
+ return true;
+}
git://git.novaco.in / novacoin.git / commitdiff