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 // Hard checkpoints of stake modifiers to ensure they are deterministic
16 static std::map<int, unsigned int> mapStakeModifierCheckpoints =
17 boost::assign::map_list_of
21 ( 12661, 0x5d84115du )
22 ( 19600, 0xdded1b8du )
25 // Get the last stake modifier and its generation time from a given block
26 static bool GetLastStakeModifier(const CBlockIndex* pindex, uint64& nStakeModifier, int64& nModifierTime)
29 return error("GetLastStakeModifier: null pindex");
30 while (pindex && pindex->pprev && !pindex->GeneratedStakeModifier())
31 pindex = pindex->pprev;
32 if (!pindex->GeneratedStakeModifier())
33 return error("GetLastStakeModifier: no generation at genesis block");
34 nStakeModifier = pindex->nStakeModifier;
35 nModifierTime = pindex->GetBlockTime();
39 // Get selection interval section (in seconds)
40 static int64 GetStakeModifierSelectionIntervalSection(int nSection)
42 assert (nSection >= 0 && nSection < 64);
43 return (nModifierInterval * 63 / (63 + ((63 - nSection) * (MODIFIER_INTERVAL_RATIO - 1))));
46 // Get stake modifier selection interval (in seconds)
47 static int64 GetStakeModifierSelectionInterval()
49 int64 nSelectionInterval = 0;
50 for (int nSection=0; nSection<64; nSection++)
51 nSelectionInterval += GetStakeModifierSelectionIntervalSection(nSection);
52 return nSelectionInterval;
55 // select a block from the candidate blocks in vSortedByTimestamp, excluding
56 // already selected blocks in vSelectedBlocks, and with timestamp up to
57 // nSelectionIntervalStop.
58 static bool SelectBlockFromCandidates(
59 vector<pair<int64, uint256> >& vSortedByTimestamp,
60 map<uint256, const CBlockIndex*>& mapSelectedBlocks,
61 int64 nSelectionIntervalStop, uint64 nStakeModifierPrev,
62 const CBlockIndex** pindexSelected)
64 bool fSelected = false;
66 *pindexSelected = (const CBlockIndex*) 0;
67 BOOST_FOREACH(const PAIRTYPE(int64, uint256)& item, vSortedByTimestamp)
69 if (!mapBlockIndex.count(item.second))
70 return error("SelectBlockFromCandidates: failed to find block index for candidate block %s", item.second.ToString().c_str());
71 const CBlockIndex* pindex = mapBlockIndex[item.second];
72 if (fSelected && pindex->GetBlockTime() > nSelectionIntervalStop)
74 if (mapSelectedBlocks.count(pindex->GetBlockHash()) > 0)
76 // compute the selection hash by hashing its proof-hash and the
77 // previous proof-of-stake modifier
78 uint256 hashProof = pindex->IsProofOfStake()? pindex->hashProofOfStake : pindex->GetBlockHash();
79 CDataStream ss(SER_GETHASH, 0);
80 ss << hashProof << nStakeModifierPrev;
81 uint256 hashSelection = Hash(ss.begin(), ss.end());
82 // the selection hash is divided by 2**32 so that proof-of-stake block
83 // is always favored over proof-of-work block. this is to preserve
84 // the energy efficiency property
85 if (pindex->IsProofOfStake())
87 if (fSelected && hashSelection < hashBest)
89 hashBest = hashSelection;
90 *pindexSelected = (const CBlockIndex*) pindex;
95 hashBest = hashSelection;
96 *pindexSelected = (const CBlockIndex*) pindex;
99 if (fDebug && GetBoolArg("-printstakemodifier"))
100 printf("SelectBlockFromCandidates: selection hash=%s\n", hashBest.ToString().c_str());
104 // Stake Modifier (hash modifier of proof-of-stake):
105 // The purpose of stake modifier is to prevent a txout (coin) owner from
106 // computing future proof-of-stake generated by this txout at the time
107 // of transaction confirmation. To meet kernel protocol, the txout
108 // must hash with a future stake modifier to generate the proof.
109 // Stake modifier consists of bits each of which is contributed from a
110 // selected block of a given block group in the past.
111 // The selection of a block is based on a hash of the block's proof-hash and
112 // the previous stake modifier.
113 // Stake modifier is recomputed at a fixed time interval instead of every
114 // block. This is to make it difficult for an attacker to gain control of
115 // additional bits in the stake modifier, even after generating a chain of
117 bool ComputeNextStakeModifier(const CBlockIndex* pindexPrev, uint64& nStakeModifier, bool& fGeneratedStakeModifier)
120 fGeneratedStakeModifier = false;
123 fGeneratedStakeModifier = true;
124 return true; // genesis block's modifier is 0
126 // First find current stake modifier and its generation block time
127 // if it's not old enough, return the same stake modifier
128 int64 nModifierTime = 0;
129 if (!GetLastStakeModifier(pindexPrev, nStakeModifier, nModifierTime))
130 return error("ComputeNextStakeModifier: unable to get last modifier");
133 printf("ComputeNextStakeModifier: prev modifier=0x%016"PRI64x" time=%s\n", nStakeModifier, DateTimeStrFormat(nModifierTime).c_str());
135 if (nModifierTime / nModifierInterval >= pindexPrev->GetBlockTime() / nModifierInterval)
138 // Sort candidate blocks by timestamp
139 vector<pair<int64, uint256> > vSortedByTimestamp;
140 vSortedByTimestamp.reserve(64 * nModifierInterval / nStakeTargetSpacing);
141 int64 nSelectionInterval = GetStakeModifierSelectionInterval();
142 int64 nSelectionIntervalStart = (pindexPrev->GetBlockTime() / nModifierInterval) * nModifierInterval - nSelectionInterval;
143 const CBlockIndex* pindex = pindexPrev;
144 while (pindex && pindex->GetBlockTime() >= nSelectionIntervalStart)
146 vSortedByTimestamp.push_back(make_pair(pindex->GetBlockTime(), pindex->GetBlockHash()));
147 pindex = pindex->pprev;
149 int nHeightFirstCandidate = pindex ? (pindex->nHeight + 1) : 0;
150 reverse(vSortedByTimestamp.begin(), vSortedByTimestamp.end());
151 sort(vSortedByTimestamp.begin(), vSortedByTimestamp.end());
153 // Select 64 blocks from candidate blocks to generate stake modifier
154 uint64 nStakeModifierNew = 0;
155 int64 nSelectionIntervalStop = nSelectionIntervalStart;
156 map<uint256, const CBlockIndex*> mapSelectedBlocks;
157 for (int nRound=0; nRound<min(64, (int)vSortedByTimestamp.size()); nRound++)
159 // add an interval section to the current selection round
160 nSelectionIntervalStop += GetStakeModifierSelectionIntervalSection(nRound);
161 // select a block from the candidates of current round
162 if (!SelectBlockFromCandidates(vSortedByTimestamp, mapSelectedBlocks, nSelectionIntervalStop, nStakeModifier, &pindex))
163 return error("ComputeNextStakeModifier: unable to select block at round %d", nRound);
164 // write the entropy bit of the selected block
165 nStakeModifierNew |= (((uint64)pindex->GetStakeEntropyBit()) << nRound);
166 // add the selected block from candidates to selected list
167 mapSelectedBlocks.insert(make_pair(pindex->GetBlockHash(), pindex));
168 if (fDebug && GetBoolArg("-printstakemodifier"))
169 printf("ComputeNextStakeModifier: selected round %d stop=%s height=%d bit=%d\n",
170 nRound, DateTimeStrFormat(nSelectionIntervalStop).c_str(), pindex->nHeight, pindex->GetStakeEntropyBit());
173 // Print selection map for visualization of the selected blocks
174 if (fDebug && GetBoolArg("-printstakemodifier"))
176 string strSelectionMap = "";
177 // '-' indicates proof-of-work blocks not selected
178 strSelectionMap.insert(0, pindexPrev->nHeight - nHeightFirstCandidate + 1, '-');
180 while (pindex && pindex->nHeight >= nHeightFirstCandidate)
182 // '=' indicates proof-of-stake blocks not selected
183 if (pindex->IsProofOfStake())
184 strSelectionMap.replace(pindex->nHeight - nHeightFirstCandidate, 1, "=");
185 pindex = pindex->pprev;
187 BOOST_FOREACH(const PAIRTYPE(uint256, const CBlockIndex*)& item, mapSelectedBlocks)
189 // 'S' indicates selected proof-of-stake blocks
190 // 'W' indicates selected proof-of-work blocks
191 strSelectionMap.replace(item.second->nHeight - nHeightFirstCandidate, 1, item.second->IsProofOfStake()? "S" : "W");
193 printf("ComputeNextStakeModifier: selection height [%d, %d] map %s\n", nHeightFirstCandidate, pindexPrev->nHeight, strSelectionMap.c_str());
197 printf("ComputeNextStakeModifier: new modifier=0x%016"PRI64x" time=%s\n", nStakeModifierNew, DateTimeStrFormat(pindexPrev->GetBlockTime()).c_str());
200 nStakeModifier = nStakeModifierNew;
201 fGeneratedStakeModifier = true;
205 // The stake modifier used to hash for a stake kernel is chosen as the stake
206 // modifier about a selection interval later than the coin generating the kernel
207 static bool GetKernelStakeModifier(uint256 hashBlockFrom, uint64& nStakeModifier, int& nStakeModifierHeight, int64& nStakeModifierTime, bool fPrintProofOfStake)
210 if (!mapBlockIndex.count(hashBlockFrom))
211 return error("GetKernelStakeModifier() : block not indexed");
212 const CBlockIndex* pindexFrom = mapBlockIndex[hashBlockFrom];
213 nStakeModifierHeight = pindexFrom->nHeight;
214 nStakeModifierTime = pindexFrom->GetBlockTime();
215 int64 nStakeModifierSelectionInterval = GetStakeModifierSelectionInterval();
216 const CBlockIndex* pindex = pindexFrom;
217 // loop to find the stake modifier later by a selection interval
218 while (nStakeModifierTime < pindexFrom->GetBlockTime() + nStakeModifierSelectionInterval)
221 { // reached best block; may happen if node is behind on block chain
222 if (fPrintProofOfStake || (pindex->GetBlockTime() + nStakeMinAge - nStakeModifierSelectionInterval > GetAdjustedTime()))
223 return error("GetKernelStakeModifier() : reached best block %s at height %d from block %s",
224 pindex->GetBlockHash().ToString().c_str(), pindex->nHeight, hashBlockFrom.ToString().c_str());
228 pindex = pindex->pnext;
229 if (pindex->GeneratedStakeModifier())
231 nStakeModifierHeight = pindex->nHeight;
232 nStakeModifierTime = pindex->GetBlockTime();
235 nStakeModifier = pindex->nStakeModifier;
239 // ppcoin kernel protocol
240 // coinstake must meet hash target according to the protocol:
241 // kernel (input 0) must meet the formula
242 // hash(nStakeModifier + txPrev.block.nTime + txPrev.offset + txPrev.nTime + txPrev.vout.n + nTime) < bnTarget * nCoinDayWeight
243 // this ensures that the chance of getting a coinstake is proportional to the
244 // amount of coin age one owns.
245 // The reason this hash is chosen is the following:
247 // (v0.3) scrambles computation to make it very difficult to precompute
248 // future proof-of-stake at the time of the coin's confirmation
249 // (v0.2) nBits (deprecated): encodes all past block timestamps
250 // txPrev.block.nTime: prevent nodes from guessing a good timestamp to
251 // generate transaction for future advantage
252 // txPrev.offset: offset of txPrev inside block, to reduce the chance of
253 // nodes generating coinstake at the same time
254 // txPrev.nTime: reduce the chance of nodes generating coinstake at the same
256 // txPrev.vout.n: output number of txPrev, to reduce the chance of nodes
257 // generating coinstake at the same time
258 // block/tx hash should not be used here as they can be generated in vast
259 // quantities so as to generate blocks faster, degrading the system back into
260 // a proof-of-work situation.
262 bool CheckStakeKernelHash(unsigned int nBits, const CBlock& blockFrom, unsigned int nTxPrevOffset, const CTransaction& txPrev, const COutPoint& prevout, unsigned int nTimeTx, uint256& hashProofOfStake, bool fPrintProofOfStake)
264 if (nTimeTx < txPrev.nTime) // Transaction timestamp violation
265 return error("CheckStakeKernelHash() : nTime violation");
267 unsigned int nTimeBlockFrom = blockFrom.GetBlockTime();
268 if (nTimeBlockFrom + nStakeMinAge > nTimeTx) // Min age requirement
269 return error("CheckStakeKernelHash() : min age violation");
271 CBigNum bnTargetPerCoinDay;
272 bnTargetPerCoinDay.SetCompact(nBits);
273 int64 nValueIn = txPrev.vout[prevout.n].nValue;
275 // v0.3 protocol kernel hash weight starts from 0 at the 30-day min age
276 // this change increases active coins participating the hash and helps
277 // to secure the network when proof-of-stake difficulty is low
278 int64 nTimeWeight = min((int64)nTimeTx - txPrev.nTime, (int64)nStakeMaxAge) - nStakeMinAge;
279 CBigNum bnCoinDayWeight = CBigNum(nValueIn) * nTimeWeight / COIN / (24 * 60 * 60);
282 CDataStream ss(SER_GETHASH, 0);
283 uint64 nStakeModifier = 0;
284 int nStakeModifierHeight = 0;
285 int64 nStakeModifierTime = 0;
287 if (!GetKernelStakeModifier(blockFrom.GetHash(), nStakeModifier, nStakeModifierHeight, nStakeModifierTime, fPrintProofOfStake))
289 ss << nStakeModifier;
291 ss << nTimeBlockFrom << nTxPrevOffset << txPrev.nTime << prevout.n << nTimeTx;
292 hashProofOfStake = Hash(ss.begin(), ss.end());
293 if (fPrintProofOfStake)
295 printf("CheckStakeKernelHash() : using modifier 0x%016"PRI64x" at height=%d timestamp=%s for block from height=%d timestamp=%s\n",
296 nStakeModifier, nStakeModifierHeight,
297 DateTimeStrFormat(nStakeModifierTime).c_str(),
298 mapBlockIndex[blockFrom.GetHash()]->nHeight,
299 DateTimeStrFormat(blockFrom.GetBlockTime()).c_str());
300 printf("CheckStakeKernelHash() : check protocol=%s modifier=0x%016"PRI64x" nTimeBlockFrom=%u nTxPrevOffset=%u nTimeTxPrev=%u nPrevout=%u nTimeTx=%u hashProof=%s\n",
303 nTimeBlockFrom, nTxPrevOffset, txPrev.nTime, prevout.n, nTimeTx,
304 hashProofOfStake.ToString().c_str());
307 // Now check if proof-of-stake hash meets target protocol
308 if (CBigNum(hashProofOfStake) > bnCoinDayWeight * bnTargetPerCoinDay)
310 if (fDebug && !fPrintProofOfStake)
312 printf("CheckStakeKernelHash() : using modifier 0x%016"PRI64x" at height=%d timestamp=%s for block from height=%d timestamp=%s\n",
313 nStakeModifier, nStakeModifierHeight,
314 DateTimeStrFormat(nStakeModifierTime).c_str(),
315 mapBlockIndex[blockFrom.GetHash()]->nHeight,
316 DateTimeStrFormat(blockFrom.GetBlockTime()).c_str());
317 printf("CheckStakeKernelHash() : pass protocol=%s modifier=0x%016"PRI64x" nTimeBlockFrom=%u nTxPrevOffset=%u nTimeTxPrev=%u nPrevout=%u nTimeTx=%u hashProof=%s\n",
320 nTimeBlockFrom, nTxPrevOffset, txPrev.nTime, prevout.n, nTimeTx,
321 hashProofOfStake.ToString().c_str());
326 // Check kernel hash target and coinstake signature
327 bool CheckProofOfStake(const CTransaction& tx, unsigned int nBits, uint256& hashProofOfStake)
329 if (!tx.IsCoinStake())
330 return error("CheckProofOfStake() : called on non-coinstake %s", tx.GetHash().ToString().c_str());
332 // Kernel (input 0) must match the stake hash target per coin age (nBits)
333 const CTxIn& txin = tx.vin[0];
335 // First try finding the previous transaction in database
339 if (!txPrev.ReadFromDisk(txdb, txin.prevout, txindex))
340 return tx.DoS(1, error("CheckProofOfStake() : INFO: read txPrev failed")); // previous transaction not in main chain, may occur during initial download
344 if (!VerifySignature(txPrev, tx, 0, true, 0))
345 return tx.DoS(100, error("CheckProofOfStake() : VerifySignature failed on coinstake %s", tx.GetHash().ToString().c_str()));
349 if (!block.ReadFromDisk(txindex.pos.nFile, txindex.pos.nBlockPos, false))
350 return fDebug? error("CheckProofOfStake() : read block failed") : false; // unable to read block of previous transaction
352 if (!CheckStakeKernelHash(nBits, block, txindex.pos.nTxPos - txindex.pos.nBlockPos, txPrev, txin.prevout, tx.nTime, hashProofOfStake, fDebug))
353 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
358 // Check whether the coinstake timestamp meets protocol
359 bool CheckCoinStakeTimestamp(int64 nTimeBlock, int64 nTimeTx)
362 return (nTimeBlock == nTimeTx);
365 // Get stake modifier checksum
366 unsigned int GetStakeModifierChecksum(const CBlockIndex* pindex)
368 assert (pindex->pprev || pindex->GetBlockHash() == (!fTestNet ? hashGenesisBlock : hashGenesisBlockTestNet));
369 // Hash previous checksum with flags, hashProofOfStake and nStakeModifier
370 CDataStream ss(SER_GETHASH, 0);
372 ss << pindex->pprev->nStakeModifierChecksum;
373 ss << pindex->nFlags << pindex->hashProofOfStake << pindex->nStakeModifier;
374 uint256 hashChecksum = Hash(ss.begin(), ss.end());
375 hashChecksum >>= (256 - 32);
376 return hashChecksum.Get64();
379 // Check stake modifier hard checkpoints
380 bool CheckStakeModifierCheckpoints(int nHeight, unsigned int nStakeModifierChecksum)
382 if (fTestNet) return true; // Testnet has no checkpoints
383 if (mapStakeModifierCheckpoints.count(nHeight))
384 return nStakeModifierChecksum == mapStakeModifierCheckpoints[nHeight];