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// Copyright (c) 2012-2013 The PPCoin developers
// Copyright (c) 2014 The TryCoin 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 "txdb.h"
using namespace std;
// Get time weight
int64_t GetWeight(int64_t nIntervalBeginning, int64_t nIntervalEnd)
{
// Kernel hash weight starts from 0 at the min age
// this change increases active coins participating the hash and helps
// to secure the network when proof-of-stake difficulty is low
return nIntervalEnd - nIntervalBeginning - nStakeMinAge;
}
// Get the last stake modifier and its generation time from a given block
static bool GetLastStakeModifier(const CBlockIndex* pindex, uint64_t& nStakeModifier, int64_t& 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_t 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_t GetStakeModifierSelectionInterval()
{
int64_t 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_t, uint256> >& vSortedByTimestamp, map<uint256, const CBlockIndex*>& mapSelectedBlocks,
int64_t nSelectionIntervalStop, uint64_t nStakeModifierPrev, const CBlockIndex** pindexSelected)
{
bool fSelected = false;
uint256 hashBest = 0;
*pindexSelected = (const CBlockIndex*) 0;
BOOST_FOREACH(const PAIRTYPE(int64_t, uint256)& item, vSortedByTimestamp)
{
if (!mapBlockIndex.count(item.second))
return error("SelectBlockFromCandidates: failed to find block index for candidate block %s", item.second.ToString());
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
CDataStream ss(SER_GETHASH, 0);
ss << pindex->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;
}
}
LogPrint("stakemodifier", "SelectBlockFromCandidates: selection hash=%s\n", hashBest.ToString());
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_t& 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_t nModifierTime = 0;
if (!GetLastStakeModifier(pindexPrev, nStakeModifier, nModifierTime))
return error("ComputeNextStakeModifier: unable to get last modifier");
LogPrint("stakemodifier", "ComputeNextStakeModifier: prev modifier=0x%016x time=%s\n", nStakeModifier, DateTimeStrFormat(nModifierTime));
if (nModifierTime / nModifierInterval >= pindexPrev->GetBlockTime() / nModifierInterval)
return true;
// Sort candidate blocks by timestamp
vector<pair<int64_t, uint256> > vSortedByTimestamp;
vSortedByTimestamp.reserve(64 * nModifierInterval / GetTargetSpacing(pindexPrev->nHeight));
int64_t nSelectionInterval = GetStakeModifierSelectionInterval();
int64_t 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_t nStakeModifierNew = 0;
int64_t 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_t)pindex->GetStakeEntropyBit()) << nRound);
// add the selected block from candidates to selected list
mapSelectedBlocks.insert(make_pair(pindex->GetBlockHash(), pindex));
LogPrint("stakemodifier", "ComputeNextStakeModifier: selected round %d stop=%s height=%d bit=%d\n", nRound, DateTimeStrFormat(nSelectionIntervalStop), pindex->nHeight, pindex->GetStakeEntropyBit());
}
// Print selection map for visualization of the selected blocks
if (LogAcceptCategory("stakemodifier"))
{
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");
}
LogPrintf("ComputeNextStakeModifier: selection height [%d, %d] map %s\n", nHeightFirstCandidate, pindexPrev->nHeight, strSelectionMap);
}
LogPrint("stakemodifier", "ComputeNextStakeModifier: new modifier=0x%016x time=%s\n", nStakeModifierNew, DateTimeStrFormat(pindexPrev->GetBlockTime()));
nStakeModifier = nStakeModifierNew;
fGeneratedStakeModifier = true;
return true;
}
// 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.
uint256 ComputeStakeModifierV2(const CBlockIndex* pindexPrev, const uint256& kernel)
{
if (!pindexPrev)
return 0; // genesis block's modifier is 0
CDataStream ss(SER_GETHASH, 0);
ss << kernel << pindexPrev->bnStakeModifierV2;
return Hash(ss.begin(), ss.end());
}
// 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_t& nStakeModifier, int& nStakeModifierHeight, int64_t& 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_t 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(), pindex->nHeight, hashBlockFrom.ToString());
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: scrambles computation to make it very difficult to precompute
// future proof-of-stake at the time of the coin's confirmation
// 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.
//
static bool CheckStakeKernelHashV1(unsigned int nBits, const CBlock& blockFrom, unsigned int nTxPrevOffset, const CTransaction& txPrev, const COutPoint& prevout, unsigned int nTimeTx, uint256& hashProofOfStake, uint256& targetProofOfStake, bool fPrintProofOfStake)
{
if (nTimeTx < txPrev.nTime) // Transaction timestamp violation
return error("CheckStakeKernelHash() : nTime violation");
unsigned int nTimeBlockFrom = blockFrom.GetBlockTime();
CBigNum bnTargetPerCoinDay;
bnTargetPerCoinDay.SetCompact(nBits);
int64_t nValueIn = txPrev.vout[prevout.n].nValue;
uint256 hashBlockFrom = blockFrom.GetHash();
CBigNum bnCoinDayWeight = CBigNum(nValueIn) * GetWeight((int64_t)txPrev.nTime, (int64_t)nTimeTx) / COIN / (24 * 60 * 60);
targetProofOfStake = (bnCoinDayWeight * bnTargetPerCoinDay).getuint256();
// Calculate hash
CDataStream ss(SER_GETHASH, 0);
uint64_t nStakeModifier = 0;
int nStakeModifierHeight = 0;
int64_t nStakeModifierTime = 0;
if (!GetKernelStakeModifier(hashBlockFrom, nStakeModifier, nStakeModifierHeight, nStakeModifierTime, fPrintProofOfStake))
return false;
ss << nStakeModifier;
ss << nTimeBlockFrom << nTxPrevOffset << txPrev.nTime << prevout.n << nTimeTx;
hashProofOfStake = Hash(ss.begin(), ss.end());
if (fPrintProofOfStake)
{
LogPrintf("CheckStakeKernelHash() : using modifier 0x%016x at height=%d timestamp=%s for block from height=%d timestamp=%s\n",
nStakeModifier, nStakeModifierHeight,
DateTimeStrFormat(nStakeModifierTime),
mapBlockIndex[hashBlockFrom]->nHeight,
DateTimeStrFormat(blockFrom.GetBlockTime()));
LogPrintf("CheckStakeKernelHash() : check modifier=0x%016x nTimeBlockFrom=%u nTxPrevOffset=%u nTimeTxPrev=%u nPrevout=%u nTimeTx=%u hashProof=%s\n",
nStakeModifier,
nTimeBlockFrom, nTxPrevOffset, txPrev.nTime, prevout.n, nTimeTx,
hashProofOfStake.ToString());
}
// Now check if proof-of-stake hash meets target protocol
if (CBigNum(hashProofOfStake) > bnCoinDayWeight * bnTargetPerCoinDay)
return false;
if (fDebug && !fPrintProofOfStake)
{
LogPrintf("CheckStakeKernelHash() : using modifier 0x%016x at height=%d timestamp=%s for block from height=%d timestamp=%s\n",
nStakeModifier, nStakeModifierHeight,
DateTimeStrFormat(nStakeModifierTime),
mapBlockIndex[hashBlockFrom]->nHeight,
DateTimeStrFormat(blockFrom.GetBlockTime()));
LogPrintf("CheckStakeKernelHash() : pass modifier=0x%016x nTimeBlockFrom=%u nTxPrevOffset=%u nTimeTxPrev=%u nPrevout=%u nTimeTx=%u hashProof=%s\n",
nStakeModifier,
nTimeBlockFrom, nTxPrevOffset, txPrev.nTime, prevout.n, nTimeTx,
hashProofOfStake.ToString());
}
return true;
}
// TryCoin kernel protocol
// coinstake must meet hash target according to the protocol:
// kernel (input 0) must meet the formula
// hash(nStakeModifier + txPrev.block.nTime + txPrev.nTime + txPrev.vout.hash + txPrev.vout.n + nTime) < bnTarget * nWeight
// this ensures that the chance of getting a coinstake is proportional to the
// amount of coins one owns.
// The reason this hash is chosen is the following:
// nStakeModifier: scrambles computation to make it very difficult to precompute
// future proof-of-stake
// txPrev.block.nTime: prevent nodes from guessing a good timestamp to
// generate transaction for future advantage,
// obsolete since v3
// txPrev.nTime: slightly scrambles computation
// txPrev.vout.hash: hash of txPrev, to 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
// nTime: current timestamp
// 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.
//
static bool CheckStakeKernelHashV2(CBlockIndex* pindexPrev, unsigned int nBits, unsigned int nTimeBlockFrom, const CTransaction& txPrev, const COutPoint& prevout, unsigned int nTimeTx, uint256& hashProofOfStake, uint256& targetProofOfStake, bool fPrintProofOfStake)
{
if (nTimeTx < txPrev.nTime) // Transaction timestamp violation
return error("CheckStakeKernelHash() : nTime violation");
// Base target
CBigNum bnTarget;
bnTarget.SetCompact(nBits);
// Weighted target
int64_t nValueIn = txPrev.vout[prevout.n].nValue;
CBigNum bnWeight = CBigNum(nValueIn);
bnTarget *= bnWeight;
targetProofOfStake = bnTarget.getuint256();
uint64_t nStakeModifier = pindexPrev->nStakeModifier;
uint256 bnStakeModifierV2 = pindexPrev->bnStakeModifierV2;
int nStakeModifierHeight = pindexPrev->nHeight;
int64_t nStakeModifierTime = pindexPrev->nTime;
// Calculate hash
CDataStream ss(SER_GETHASH, 0);
if (IsProtocolV3(nTimeTx))
ss << bnStakeModifierV2;
else
ss << nStakeModifier << nTimeBlockFrom;
ss << txPrev.nTime << prevout.hash << prevout.n << nTimeTx;
hashProofOfStake = Hash(ss.begin(), ss.end());
if (fPrintProofOfStake)
{
LogPrintf("CheckStakeKernelHash() : using modifier 0x%016x at height=%d timestamp=%s for block from timestamp=%s\n",
nStakeModifier, nStakeModifierHeight,
DateTimeStrFormat(nStakeModifierTime),
DateTimeStrFormat(nTimeBlockFrom));
LogPrintf("CheckStakeKernelHash() : check modifier=0x%016x nTimeBlockFrom=%u nTimeTxPrev=%u nPrevout=%u nTimeTx=%u hashProof=%s\n",
nStakeModifier,
nTimeBlockFrom, txPrev.nTime, prevout.n, nTimeTx,
hashProofOfStake.ToString());
}
// Now check if proof-of-stake hash meets target protocol
if (CBigNum(hashProofOfStake) > bnTarget)
return false;
if (fDebug && !fPrintProofOfStake)
{
LogPrintf("CheckStakeKernelHash() : using modifier 0x%016x at height=%d timestamp=%s for block from timestamp=%s\n",
nStakeModifier, nStakeModifierHeight,
DateTimeStrFormat(nStakeModifierTime),
DateTimeStrFormat(nTimeBlockFrom));
LogPrintf("CheckStakeKernelHash() : pass modifier=0x%016x nTimeBlockFrom=%u nTimeTxPrev=%u nPrevout=%u nTimeTx=%u hashProof=%s\n",
nStakeModifier,
nTimeBlockFrom, txPrev.nTime, prevout.n, nTimeTx,
hashProofOfStake.ToString());
}
return true;
}
bool CheckStakeKernelHash(CBlockIndex* pindexPrev, unsigned int nBits, const CBlock& blockFrom, unsigned int nTxPrevOffset, const CTransaction& txPrev, const COutPoint& prevout, unsigned int nTimeTx, uint256& hashProofOfStake, uint256& targetProofOfStake, bool fPrintProofOfStake)
{
if (IsProtocolV2(pindexPrev->nHeight+1))
return CheckStakeKernelHashV2(pindexPrev, nBits, blockFrom.GetBlockTime(), txPrev, prevout, nTimeTx, hashProofOfStake, targetProofOfStake, fPrintProofOfStake);
else
return CheckStakeKernelHashV1(nBits, blockFrom, nTxPrevOffset, txPrev, prevout, nTimeTx, hashProofOfStake, targetProofOfStake, fPrintProofOfStake);
}
// Check kernel hash target and coinstake signature
bool CheckProofOfStake(CBlockIndex* pindexPrev, const CTransaction& tx, unsigned int nBits, uint256& hashProofOfStake, uint256& targetProofOfStake)
{
if (!tx.IsCoinStake())
return error("CheckProofOfStake() : called on non-coinstake %s", tx.GetHash().ToString());
// 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
// Verify signature
if (!VerifySignature(txPrev, tx, 0, SCRIPT_VERIFY_NONE, 0))
return tx.DoS(100, error("CheckProofOfStake() : VerifySignature failed on coinstake %s", tx.GetHash().ToString()));
// 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
// Min age requirement
if (IsProtocolV3(tx.nTime))
{
int nDepth;
if (IsConfirmedInNPrevBlocks(txindex, pindexPrev, nStakeMinConfirmations - 1, nDepth))
return tx.DoS(100, error("CheckProofOfStake() : tried to stake at depth %d", nDepth + 1));
}
else
{
unsigned int nTimeBlockFrom = block.GetBlockTime();
if (nTimeBlockFrom + nStakeMinAge > tx.nTime)
return error("CheckProofOfStake() : min age violation");
}
if (!CheckStakeKernelHash(pindexPrev, nBits, block, txindex.pos.nTxPos - txindex.pos.nBlockPos, txPrev, txin.prevout, tx.nTime, hashProofOfStake, targetProofOfStake, fDebug))
return tx.DoS(1, error("CheckProofOfStake() : INFO: check kernel failed on coinstake %s, hashProof=%s", tx.GetHash().ToString(), hashProofOfStake.ToString())); // may occur during initial download or if behind on block chain sync
return true;
}
// Check whether the coinstake timestamp meets protocol
bool CheckCoinStakeTimestamp(int nHeight, int64_t nTimeBlock, int64_t nTimeTx)
{
if (IsProtocolV2(nHeight))
return (nTimeBlock == nTimeTx) && ((nTimeTx & STAKE_TIMESTAMP_MASK) == 0);
else
return (nTimeBlock == nTimeTx);
}
bool CheckKernel(CBlockIndex* pindexPrev, unsigned int nBits, int64_t nTime, const COutPoint& prevout, int64_t* pBlockTime)
{
uint256 hashProofOfStake, targetProofOfStake;
CTxDB txdb("r");
CTransaction txPrev;
CTxIndex txindex;
if (!txPrev.ReadFromDisk(txdb, prevout, txindex))
return false;
// Read block header
CBlock block;
if (!block.ReadFromDisk(txindex.pos.nFile, txindex.pos.nBlockPos, false))
return false;
if (IsProtocolV3(nTime))
{
int nDepth;
if (IsConfirmedInNPrevBlocks(txindex, pindexPrev, nStakeMinConfirmations - 1, nDepth))
return false;
}
else
{
if (block.GetBlockTime() + nStakeMinAge > nTime)
return false; // only count coins meeting min age requirement
}
if (pBlockTime)
*pBlockTime = block.GetBlockTime();
return CheckStakeKernelHash(pindexPrev, nBits, block, txindex.pos.nTxPos - txindex.pos.nBlockPos, txPrev, prevout, nTime, hashProofOfStake, targetProofOfStake);
}
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