1 // Copyright (c) 2012-2013 The PPCoin developers
2 // Distributed under the MIT/X11 software license, see the accompanying
3 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
5 #include <boost/assign/list_of.hpp>
12 extern int nStakeMaxAge;
13 extern int nStakeTargetSpacing;
15 typedef std::map<int, unsigned int> MapModifierCheckpoints;
17 // Hard checkpoints of stake modifiers to ensure they are deterministic
18 static std::map<int, unsigned int> mapStakeModifierCheckpoints =
19 boost::assign::map_list_of
23 ( 12661, 0x5d84115du )
24 ( 19600, 0xdded1b8du )
25 ( 21800, 0x0daa1aaau )
26 ( 26174, 0xaf9983dcu )
29 // Hard checkpoints of stake modifiers to ensure they are deterministic (testNet)
30 static std::map<int, unsigned int> mapStakeModifierCheckpointsTestNet =
31 boost::assign::map_list_of
35 // Get the last stake modifier and its generation time from a given block
36 static bool GetLastStakeModifier(const CBlockIndex* pindex, uint64& nStakeModifier, int64& nModifierTime)
39 return error("GetLastStakeModifier: null pindex");
40 while (pindex && pindex->pprev && !pindex->GeneratedStakeModifier())
41 pindex = pindex->pprev;
42 if (!pindex->GeneratedStakeModifier())
43 return error("GetLastStakeModifier: no generation at genesis block");
44 nStakeModifier = pindex->nStakeModifier;
45 nModifierTime = pindex->GetBlockTime();
49 // Get selection interval section (in seconds)
50 static int64 GetStakeModifierSelectionIntervalSection(int nSection)
52 assert (nSection >= 0 && nSection < 64);
53 return (nModifierInterval * 63 / (63 + ((63 - nSection) * (MODIFIER_INTERVAL_RATIO - 1))));
56 // Get stake modifier selection interval (in seconds)
57 static int64 GetStakeModifierSelectionInterval()
59 int64 nSelectionInterval = 0;
60 for (int nSection=0; nSection<64; nSection++)
61 nSelectionInterval += GetStakeModifierSelectionIntervalSection(nSection);
62 return nSelectionInterval;
65 // select a block from the candidate blocks in vSortedByTimestamp, excluding
66 // already selected blocks in vSelectedBlocks, and with timestamp up to
67 // nSelectionIntervalStop.
68 static bool SelectBlockFromCandidates(
69 vector<pair<int64, uint256> >& vSortedByTimestamp,
70 map<uint256, const CBlockIndex*>& mapSelectedBlocks,
71 int64 nSelectionIntervalStop, uint64 nStakeModifierPrev,
72 const CBlockIndex** pindexSelected)
74 bool fSelected = false;
76 *pindexSelected = (const CBlockIndex*) 0;
77 BOOST_FOREACH(const PAIRTYPE(int64, uint256)& item, vSortedByTimestamp)
79 if (!mapBlockIndex.count(item.second))
80 return error("SelectBlockFromCandidates: failed to find block index for candidate block %s", item.second.ToString().c_str());
81 const CBlockIndex* pindex = mapBlockIndex[item.second];
82 if (fSelected && pindex->GetBlockTime() > nSelectionIntervalStop)
84 if (mapSelectedBlocks.count(pindex->GetBlockHash()) > 0)
86 // compute the selection hash by hashing its proof-hash and the
87 // previous proof-of-stake modifier
88 uint256 hashProof = pindex->IsProofOfStake()? pindex->hashProofOfStake : pindex->GetBlockHash();
89 CDataStream ss(SER_GETHASH, 0);
90 ss << hashProof << nStakeModifierPrev;
91 uint256 hashSelection = Hash(ss.begin(), ss.end());
92 // the selection hash is divided by 2**32 so that proof-of-stake block
93 // is always favored over proof-of-work block. this is to preserve
94 // the energy efficiency property
95 if (pindex->IsProofOfStake())
97 if (fSelected && hashSelection < hashBest)
99 hashBest = hashSelection;
100 *pindexSelected = (const CBlockIndex*) pindex;
105 hashBest = hashSelection;
106 *pindexSelected = (const CBlockIndex*) pindex;
109 if (fDebug && GetBoolArg("-printstakemodifier"))
110 printf("SelectBlockFromCandidates: selection hash=%s\n", hashBest.ToString().c_str());
114 // Stake Modifier (hash modifier of proof-of-stake):
115 // The purpose of stake modifier is to prevent a txout (coin) owner from
116 // computing future proof-of-stake generated by this txout at the time
117 // of transaction confirmation. To meet kernel protocol, the txout
118 // must hash with a future stake modifier to generate the proof.
119 // Stake modifier consists of bits each of which is contributed from a
120 // selected block of a given block group in the past.
121 // The selection of a block is based on a hash of the block's proof-hash and
122 // the previous stake modifier.
123 // Stake modifier is recomputed at a fixed time interval instead of every
124 // block. This is to make it difficult for an attacker to gain control of
125 // additional bits in the stake modifier, even after generating a chain of
127 bool ComputeNextStakeModifier(const CBlockIndex* pindexPrev, uint64& nStakeModifier, bool& fGeneratedStakeModifier)
130 fGeneratedStakeModifier = false;
133 fGeneratedStakeModifier = true;
134 return true; // genesis block's modifier is 0
136 // First find current stake modifier and its generation block time
137 // if it's not old enough, return the same stake modifier
138 int64 nModifierTime = 0;
139 if (!GetLastStakeModifier(pindexPrev, nStakeModifier, nModifierTime))
140 return error("ComputeNextStakeModifier: unable to get last modifier");
143 printf("ComputeNextStakeModifier: prev modifier=0x%016"PRI64x" time=%s\n", nStakeModifier, DateTimeStrFormat(nModifierTime).c_str());
145 if (nModifierTime / nModifierInterval >= pindexPrev->GetBlockTime() / nModifierInterval)
148 // Sort candidate blocks by timestamp
149 vector<pair<int64, uint256> > vSortedByTimestamp;
150 vSortedByTimestamp.reserve(64 * nModifierInterval / nStakeTargetSpacing);
151 int64 nSelectionInterval = GetStakeModifierSelectionInterval();
152 int64 nSelectionIntervalStart = (pindexPrev->GetBlockTime() / nModifierInterval) * nModifierInterval - nSelectionInterval;
153 const CBlockIndex* pindex = pindexPrev;
154 while (pindex && pindex->GetBlockTime() >= nSelectionIntervalStart)
156 vSortedByTimestamp.push_back(make_pair(pindex->GetBlockTime(), pindex->GetBlockHash()));
157 pindex = pindex->pprev;
159 int nHeightFirstCandidate = pindex ? (pindex->nHeight + 1) : 0;
160 reverse(vSortedByTimestamp.begin(), vSortedByTimestamp.end());
161 sort(vSortedByTimestamp.begin(), vSortedByTimestamp.end());
163 // Select 64 blocks from candidate blocks to generate stake modifier
164 uint64 nStakeModifierNew = 0;
165 int64 nSelectionIntervalStop = nSelectionIntervalStart;
166 map<uint256, const CBlockIndex*> mapSelectedBlocks;
167 for (int nRound=0; nRound<min(64, (int)vSortedByTimestamp.size()); nRound++)
169 // add an interval section to the current selection round
170 nSelectionIntervalStop += GetStakeModifierSelectionIntervalSection(nRound);
171 // select a block from the candidates of current round
172 if (!SelectBlockFromCandidates(vSortedByTimestamp, mapSelectedBlocks, nSelectionIntervalStop, nStakeModifier, &pindex))
173 return error("ComputeNextStakeModifier: unable to select block at round %d", nRound);
174 // write the entropy bit of the selected block
175 nStakeModifierNew |= (((uint64)pindex->GetStakeEntropyBit()) << nRound);
176 // add the selected block from candidates to selected list
177 mapSelectedBlocks.insert(make_pair(pindex->GetBlockHash(), pindex));
178 if (fDebug && GetBoolArg("-printstakemodifier"))
179 printf("ComputeNextStakeModifier: selected round %d stop=%s height=%d bit=%d\n",
180 nRound, DateTimeStrFormat(nSelectionIntervalStop).c_str(), pindex->nHeight, pindex->GetStakeEntropyBit());
183 // Print selection map for visualization of the selected blocks
184 if (fDebug && GetBoolArg("-printstakemodifier"))
186 string strSelectionMap = "";
187 // '-' indicates proof-of-work blocks not selected
188 strSelectionMap.insert(0, pindexPrev->nHeight - nHeightFirstCandidate + 1, '-');
190 while (pindex && pindex->nHeight >= nHeightFirstCandidate)
192 // '=' indicates proof-of-stake blocks not selected
193 if (pindex->IsProofOfStake())
194 strSelectionMap.replace(pindex->nHeight - nHeightFirstCandidate, 1, "=");
195 pindex = pindex->pprev;
197 BOOST_FOREACH(const PAIRTYPE(uint256, const CBlockIndex*)& item, mapSelectedBlocks)
199 // 'S' indicates selected proof-of-stake blocks
200 // 'W' indicates selected proof-of-work blocks
201 strSelectionMap.replace(item.second->nHeight - nHeightFirstCandidate, 1, item.second->IsProofOfStake()? "S" : "W");
203 printf("ComputeNextStakeModifier: selection height [%d, %d] map %s\n", nHeightFirstCandidate, pindexPrev->nHeight, strSelectionMap.c_str());
207 printf("ComputeNextStakeModifier: new modifier=0x%016"PRI64x" time=%s\n", nStakeModifierNew, DateTimeStrFormat(pindexPrev->GetBlockTime()).c_str());
210 nStakeModifier = nStakeModifierNew;
211 fGeneratedStakeModifier = true;
215 // The stake modifier used to hash for a stake kernel is chosen as the stake
216 // modifier about a selection interval later than the coin generating the kernel
217 static bool GetKernelStakeModifier(uint256 hashBlockFrom, uint64& nStakeModifier, int& nStakeModifierHeight, int64& nStakeModifierTime, bool fPrintProofOfStake)
220 if (!mapBlockIndex.count(hashBlockFrom))
221 return error("GetKernelStakeModifier() : block not indexed");
222 const CBlockIndex* pindexFrom = mapBlockIndex[hashBlockFrom];
223 nStakeModifierHeight = pindexFrom->nHeight;
224 nStakeModifierTime = pindexFrom->GetBlockTime();
225 int64 nStakeModifierSelectionInterval = GetStakeModifierSelectionInterval();
226 const CBlockIndex* pindex = pindexFrom;
227 // loop to find the stake modifier later by a selection interval
228 while (nStakeModifierTime < pindexFrom->GetBlockTime() + nStakeModifierSelectionInterval)
231 { // reached best block; may happen if node is behind on block chain
232 if (fPrintProofOfStake || (pindex->GetBlockTime() + nStakeMinAge - nStakeModifierSelectionInterval > GetAdjustedTime()))
233 return error("GetKernelStakeModifier() : reached best block %s at height %d from block %s",
234 pindex->GetBlockHash().ToString().c_str(), pindex->nHeight, hashBlockFrom.ToString().c_str());
238 pindex = pindex->pnext;
239 if (pindex->GeneratedStakeModifier())
241 nStakeModifierHeight = pindex->nHeight;
242 nStakeModifierTime = pindex->GetBlockTime();
245 nStakeModifier = pindex->nStakeModifier;
249 // ppcoin kernel protocol
250 // coinstake must meet hash target according to the protocol:
251 // kernel (input 0) must meet the formula
252 // hash(nStakeModifier + txPrev.block.nTime + txPrev.offset + txPrev.nTime + txPrev.vout.n + nTime) < bnTarget * nCoinDayWeight
253 // this ensures that the chance of getting a coinstake is proportional to the
254 // amount of coin age one owns.
255 // The reason this hash is chosen is the following:
257 // (v0.3) scrambles computation to make it very difficult to precompute
258 // future proof-of-stake at the time of the coin's confirmation
259 // (v0.2) nBits (deprecated): encodes all past block timestamps
260 // txPrev.block.nTime: prevent nodes from guessing a good timestamp to
261 // generate transaction for future advantage
262 // txPrev.offset: offset of txPrev inside block, to reduce the chance of
263 // nodes generating coinstake at the same time
264 // txPrev.nTime: reduce the chance of nodes generating coinstake at the same
266 // txPrev.vout.n: output number of txPrev, to reduce the chance of nodes
267 // generating coinstake at the same time
268 // block/tx hash should not be used here as they can be generated in vast
269 // quantities so as to generate blocks faster, degrading the system back into
270 // a proof-of-work situation.
272 bool CheckStakeKernelHash(unsigned int nBits, const CBlock& blockFrom, unsigned int nTxPrevOffset, const CTransaction& txPrev, const COutPoint& prevout, unsigned int nTimeTx, uint256& hashProofOfStake, bool fPrintProofOfStake)
274 if (nTimeTx < txPrev.nTime) // Transaction timestamp violation
275 return error("CheckStakeKernelHash() : nTime violation");
277 unsigned int nTimeBlockFrom = blockFrom.GetBlockTime();
278 if (nTimeBlockFrom + nStakeMinAge > nTimeTx) // Min age requirement
279 return error("CheckStakeKernelHash() : min age violation");
281 CBigNum bnTargetPerCoinDay;
282 bnTargetPerCoinDay.SetCompact(nBits);
283 int64 nValueIn = txPrev.vout[prevout.n].nValue;
287 // Kernel hash weight starts from 0 at the 30-day min age
288 // this change increases active coins participating the hash and helps
289 // to secure the network when proof-of-stake difficulty is low
291 if(fTestNet || (STAKEWEIGHT_SWITCH_TIME < nTimeTx))
293 // New rule since 01 Jan 2014: Maximum TimeWeight is 90 days.
294 nTimeWeight = min((int64)nTimeTx - txPrev.nTime - nStakeMinAge, (int64)nStakeMaxAge);
298 // Current rule: Maximum TimeWeight is 60 days.
299 nTimeWeight = min((int64)nTimeTx - txPrev.nTime, (int64)nStakeMaxAge) - nStakeMinAge;
302 CBigNum bnCoinDayWeight = CBigNum(nValueIn) * nTimeWeight / COIN / (24 * 60 * 60);
305 CDataStream ss(SER_GETHASH, 0);
306 uint64 nStakeModifier = 0;
307 int nStakeModifierHeight = 0;
308 int64 nStakeModifierTime = 0;
310 if (!GetKernelStakeModifier(blockFrom.GetHash(), nStakeModifier, nStakeModifierHeight, nStakeModifierTime, fPrintProofOfStake))
312 ss << nStakeModifier;
314 ss << nTimeBlockFrom << nTxPrevOffset << txPrev.nTime << prevout.n << nTimeTx;
315 hashProofOfStake = Hash(ss.begin(), ss.end());
316 if (fPrintProofOfStake)
318 printf("CheckStakeKernelHash() : using modifier 0x%016"PRI64x" at height=%d timestamp=%s for block from height=%d timestamp=%s\n",
319 nStakeModifier, nStakeModifierHeight,
320 DateTimeStrFormat(nStakeModifierTime).c_str(),
321 mapBlockIndex[blockFrom.GetHash()]->nHeight,
322 DateTimeStrFormat(blockFrom.GetBlockTime()).c_str());
323 printf("CheckStakeKernelHash() : check protocol=%s modifier=0x%016"PRI64x" nTimeBlockFrom=%u nTxPrevOffset=%u nTimeTxPrev=%u nPrevout=%u nTimeTx=%u hashProof=%s\n",
326 nTimeBlockFrom, nTxPrevOffset, txPrev.nTime, prevout.n, nTimeTx,
327 hashProofOfStake.ToString().c_str());
330 // Now check if proof-of-stake hash meets target protocol
331 if (CBigNum(hashProofOfStake) > bnCoinDayWeight * bnTargetPerCoinDay)
333 if (fDebug && !fPrintProofOfStake)
335 printf("CheckStakeKernelHash() : using modifier 0x%016"PRI64x" at height=%d timestamp=%s for block from height=%d timestamp=%s\n",
336 nStakeModifier, nStakeModifierHeight,
337 DateTimeStrFormat(nStakeModifierTime).c_str(),
338 mapBlockIndex[blockFrom.GetHash()]->nHeight,
339 DateTimeStrFormat(blockFrom.GetBlockTime()).c_str());
340 printf("CheckStakeKernelHash() : pass protocol=%s modifier=0x%016"PRI64x" nTimeBlockFrom=%u nTxPrevOffset=%u nTimeTxPrev=%u nPrevout=%u nTimeTx=%u hashProof=%s\n",
343 nTimeBlockFrom, nTxPrevOffset, txPrev.nTime, prevout.n, nTimeTx,
344 hashProofOfStake.ToString().c_str());
349 // Check kernel hash target and coinstake signature
350 bool CheckProofOfStake(const CTransaction& tx, unsigned int nBits, uint256& hashProofOfStake)
352 if (!tx.IsCoinStake())
353 return error("CheckProofOfStake() : called on non-coinstake %s", tx.GetHash().ToString().c_str());
355 // Kernel (input 0) must match the stake hash target per coin age (nBits)
356 const CTxIn& txin = tx.vin[0];
358 // First try finding the previous transaction in database
362 if (!txPrev.ReadFromDisk(txdb, txin.prevout, txindex))
363 return tx.DoS(1, error("CheckProofOfStake() : INFO: read txPrev failed")); // previous transaction not in main chain, may occur during initial download
367 if (!VerifySignature(txPrev, tx, 0, true, 0))
368 return tx.DoS(100, error("CheckProofOfStake() : VerifySignature failed on coinstake %s", tx.GetHash().ToString().c_str()));
372 if (!block.ReadFromDisk(txindex.pos.nFile, txindex.pos.nBlockPos, false))
373 return fDebug? error("CheckProofOfStake() : read block failed") : false; // unable to read block of previous transaction
375 if (!CheckStakeKernelHash(nBits, block, txindex.pos.nTxPos - txindex.pos.nBlockPos, txPrev, txin.prevout, tx.nTime, hashProofOfStake, fDebug))
376 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
381 // Check whether the coinstake timestamp meets protocol
382 bool CheckCoinStakeTimestamp(int64 nTimeBlock, int64 nTimeTx)
385 return (nTimeBlock == nTimeTx);
388 // Get stake modifier checksum
389 unsigned int GetStakeModifierChecksum(const CBlockIndex* pindex)
391 assert (pindex->pprev || pindex->GetBlockHash() == (!fTestNet ? hashGenesisBlock : hashGenesisBlockTestNet));
392 // Hash previous checksum with flags, hashProofOfStake and nStakeModifier
393 CDataStream ss(SER_GETHASH, 0);
395 ss << pindex->pprev->nStakeModifierChecksum;
396 ss << pindex->nFlags << pindex->hashProofOfStake << pindex->nStakeModifier;
397 uint256 hashChecksum = Hash(ss.begin(), ss.end());
398 hashChecksum >>= (256 - 32);
399 return hashChecksum.Get64();
402 // Check stake modifier hard checkpoints
403 bool CheckStakeModifierCheckpoints(int nHeight, unsigned int nStakeModifierChecksum)
405 MapModifierCheckpoints& checkpoints = (fTestNet ? mapStakeModifierCheckpointsTestNet : mapStakeModifierCheckpoints);
407 if (checkpoints.count(nHeight))
408 return nStakeModifierChecksum == checkpoints[nHeight];