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 // Modifier interval: time to elapse before new modifier is computed
13 // Set to 6-hour for production network and 20-minute for test network
14 unsigned int nModifierInterval = MODIFIER_INTERVAL;
16 // Hard checkpoints of stake modifiers to ensure they are deterministic
17 static std::map<int, unsigned int> mapStakeModifierCheckpoints =
18 boost::assign::map_list_of
23 // Get the last stake modifier and its generation time from a given block
24 static bool GetLastStakeModifier(const CBlockIndex* pindex, uint64& nStakeModifier, int64& nModifierTime)
27 return error("GetLastStakeModifier: null pindex");
28 while (pindex && pindex->pprev && !pindex->GeneratedStakeModifier())
29 pindex = pindex->pprev;
30 if (!pindex->GeneratedStakeModifier())
31 return error("GetLastStakeModifier: no generation at genesis block");
32 nStakeModifier = pindex->nStakeModifier;
33 nModifierTime = pindex->GetBlockTime();
37 // Get selection interval section (in seconds)
38 static int64 GetStakeModifierSelectionIntervalSection(int nSection)
40 assert (nSection >= 0 && nSection < 64);
41 return (nModifierInterval * 63 / (63 + ((63 - nSection) * (MODIFIER_INTERVAL_RATIO - 1))));
44 // Get stake modifier selection interval (in seconds)
45 static int64 GetStakeModifierSelectionInterval()
47 int64 nSelectionInterval = 0;
48 for (int nSection=0; nSection<64; nSection++)
49 nSelectionInterval += GetStakeModifierSelectionIntervalSection(nSection);
50 return nSelectionInterval;
53 // select a block from the candidate blocks in vSortedByTimestamp, excluding
54 // already selected blocks in vSelectedBlocks, and with timestamp up to
55 // nSelectionIntervalStop.
56 static bool SelectBlockFromCandidates(
57 vector<pair<int64, uint256> >& vSortedByTimestamp,
58 map<uint256, const CBlockIndex*>& mapSelectedBlocks,
59 int64 nSelectionIntervalStop, uint64 nStakeModifierPrev,
60 const CBlockIndex** pindexSelected)
62 bool fSelected = false;
64 *pindexSelected = (const CBlockIndex*) 0;
65 BOOST_FOREACH(const PAIRTYPE(int64, uint256)& item, vSortedByTimestamp)
67 if (!mapBlockIndex.count(item.second))
68 return error("SelectBlockFromCandidates: failed to find block index for candidate block %s", item.second.ToString().c_str());
69 const CBlockIndex* pindex = mapBlockIndex[item.second];
70 if (fSelected && pindex->GetBlockTime() > nSelectionIntervalStop)
72 if (mapSelectedBlocks.count(pindex->GetBlockHash()) > 0)
74 // compute the selection hash by hashing its proof-hash and the
75 // previous proof-of-stake modifier
76 uint256 hashProof = pindex->IsProofOfStake()? pindex->hashProofOfStake : pindex->GetBlockHash();
77 CDataStream ss(SER_GETHASH, 0);
78 ss << hashProof << nStakeModifierPrev;
79 uint256 hashSelection = Hash(ss.begin(), ss.end());
80 // the selection hash is divided by 2**32 so that proof-of-stake block
81 // is always favored over proof-of-work block. this is to preserve
82 // the energy efficiency property
83 if (pindex->IsProofOfStake())
85 if (fSelected && hashSelection < hashBest)
87 hashBest = hashSelection;
88 *pindexSelected = (const CBlockIndex*) pindex;
93 hashBest = hashSelection;
94 *pindexSelected = (const CBlockIndex*) pindex;
97 if (fDebug && GetBoolArg("-printstakemodifier"))
98 printf("SelectBlockFromCandidates: selection hash=%s\n", hashBest.ToString().c_str());
102 // Stake Modifier (hash modifier of proof-of-stake):
103 // The purpose of stake modifier is to prevent a txout (coin) owner from
104 // computing future proof-of-stake generated by this txout at the time
105 // of transaction confirmation. To meet kernel protocol, the txout
106 // must hash with a future stake modifier to generate the proof.
107 // Stake modifier consists of bits each of which is contributed from a
108 // selected block of a given block group in the past.
109 // The selection of a block is based on a hash of the block's proof-hash and
110 // the previous stake modifier.
111 // Stake modifier is recomputed at a fixed time interval instead of every
112 // block. This is to make it difficult for an attacker to gain control of
113 // additional bits in the stake modifier, even after generating a chain of
115 bool ComputeNextStakeModifier(const CBlockIndex* pindexPrev, uint64& nStakeModifier, bool& fGeneratedStakeModifier)
118 fGeneratedStakeModifier = false;
121 fGeneratedStakeModifier = true;
122 return true; // genesis block's modifier is 0
124 // First find current stake modifier and its generation block time
125 // if it's not old enough, return the same stake modifier
126 int64 nModifierTime = 0;
127 if (!GetLastStakeModifier(pindexPrev, nStakeModifier, nModifierTime))
128 return error("ComputeNextStakeModifier: unable to get last modifier");
131 printf("ComputeNextStakeModifier: prev modifier=0x%016"PRI64x" time=%s\n", nStakeModifier, DateTimeStrFormat(nModifierTime).c_str());
133 if (nModifierTime / nModifierInterval >= pindexPrev->GetBlockTime() / nModifierInterval)
136 // Sort candidate blocks by timestamp
137 vector<pair<int64, uint256> > vSortedByTimestamp;
138 vSortedByTimestamp.reserve(64 * nModifierInterval / STAKE_TARGET_SPACING);
139 int64 nSelectionInterval = GetStakeModifierSelectionInterval();
140 int64 nSelectionIntervalStart = (pindexPrev->GetBlockTime() / nModifierInterval) * nModifierInterval - nSelectionInterval;
141 const CBlockIndex* pindex = pindexPrev;
142 while (pindex && pindex->GetBlockTime() >= nSelectionIntervalStart)
144 vSortedByTimestamp.push_back(make_pair(pindex->GetBlockTime(), pindex->GetBlockHash()));
145 pindex = pindex->pprev;
147 int nHeightFirstCandidate = pindex ? (pindex->nHeight + 1) : 0;
148 reverse(vSortedByTimestamp.begin(), vSortedByTimestamp.end());
149 sort(vSortedByTimestamp.begin(), vSortedByTimestamp.end());
151 // Select 64 blocks from candidate blocks to generate stake modifier
152 uint64 nStakeModifierNew = 0;
153 int64 nSelectionIntervalStop = nSelectionIntervalStart;
154 map<uint256, const CBlockIndex*> mapSelectedBlocks;
155 for (int nRound=0; nRound<min(64, (int)vSortedByTimestamp.size()); nRound++)
157 // add an interval section to the current selection round
158 nSelectionIntervalStop += GetStakeModifierSelectionIntervalSection(nRound);
159 // select a block from the candidates of current round
160 if (!SelectBlockFromCandidates(vSortedByTimestamp, mapSelectedBlocks, nSelectionIntervalStop, nStakeModifier, &pindex))
161 return error("ComputeNextStakeModifier: unable to select block at round %d", nRound);
162 // write the entropy bit of the selected block
163 nStakeModifierNew |= (((uint64)pindex->GetStakeEntropyBit()) << nRound);
164 // add the selected block from candidates to selected list
165 mapSelectedBlocks.insert(make_pair(pindex->GetBlockHash(), pindex));
166 if (fDebug && GetBoolArg("-printstakemodifier"))
167 printf("ComputeNextStakeModifier: selected round %d stop=%s height=%d bit=%d\n",
168 nRound, DateTimeStrFormat(nSelectionIntervalStop).c_str(), pindex->nHeight, pindex->GetStakeEntropyBit());
171 // Print selection map for visualization of the selected blocks
172 if (fDebug && GetBoolArg("-printstakemodifier"))
174 string strSelectionMap = "";
175 // '-' indicates proof-of-work blocks not selected
176 strSelectionMap.insert(0, pindexPrev->nHeight - nHeightFirstCandidate + 1, '-');
178 while (pindex && pindex->nHeight >= nHeightFirstCandidate)
180 // '=' indicates proof-of-stake blocks not selected
181 if (pindex->IsProofOfStake())
182 strSelectionMap.replace(pindex->nHeight - nHeightFirstCandidate, 1, "=");
183 pindex = pindex->pprev;
185 BOOST_FOREACH(const PAIRTYPE(uint256, const CBlockIndex*)& item, mapSelectedBlocks)
187 // 'S' indicates selected proof-of-stake blocks
188 // 'W' indicates selected proof-of-work blocks
189 strSelectionMap.replace(item.second->nHeight - nHeightFirstCandidate, 1, item.second->IsProofOfStake()? "S" : "W");
191 printf("ComputeNextStakeModifier: selection height [%d, %d] map %s\n", nHeightFirstCandidate, pindexPrev->nHeight, strSelectionMap.c_str());
195 printf("ComputeNextStakeModifier: new modifier=0x%016"PRI64x" time=%s\n", nStakeModifierNew, DateTimeStrFormat(pindexPrev->GetBlockTime()).c_str());
198 nStakeModifier = nStakeModifierNew;
199 fGeneratedStakeModifier = true;
203 // The stake modifier used to hash for a stake kernel is chosen as the stake
204 // modifier about a selection interval later than the coin generating the kernel
205 static bool GetKernelStakeModifier(uint256 hashBlockFrom, uint64& nStakeModifier, int& nStakeModifierHeight, int64& nStakeModifierTime, bool fPrintProofOfStake)
208 if (!mapBlockIndex.count(hashBlockFrom))
209 return error("GetKernelStakeModifier() : block not indexed");
210 const CBlockIndex* pindexFrom = mapBlockIndex[hashBlockFrom];
211 nStakeModifierHeight = pindexFrom->nHeight;
212 nStakeModifierTime = pindexFrom->GetBlockTime();
213 int64 nStakeModifierSelectionInterval = GetStakeModifierSelectionInterval();
214 const CBlockIndex* pindex = pindexFrom;
215 // loop to find the stake modifier later by a selection interval
216 while (nStakeModifierTime < pindexFrom->GetBlockTime() + nStakeModifierSelectionInterval)
219 { // reached best block; may happen if node is behind on block chain
220 if (fPrintProofOfStake || (pindex->GetBlockTime() + nStakeMinAge - nStakeModifierSelectionInterval > GetAdjustedTime()))
221 return error("GetKernelStakeModifier() : reached best block %s at height %d from block %s",
222 pindex->GetBlockHash().ToString().c_str(), pindex->nHeight, hashBlockFrom.ToString().c_str());
226 pindex = pindex->pnext;
227 if (pindex->GeneratedStakeModifier())
229 nStakeModifierHeight = pindex->nHeight;
230 nStakeModifierTime = pindex->GetBlockTime();
233 nStakeModifier = pindex->nStakeModifier;
237 // ppcoin kernel protocol
238 // coinstake must meet hash target according to the protocol:
239 // kernel (input 0) must meet the formula
240 // hash(nStakeModifier + txPrev.block.nTime + txPrev.offset + txPrev.nTime + txPrev.vout.n + nTime) < bnTarget * nCoinDayWeight
241 // this ensures that the chance of getting a coinstake is proportional to the
242 // amount of coin age one owns.
243 // The reason this hash is chosen is the following:
245 // (v0.3) scrambles computation to make it very difficult to precompute
246 // future proof-of-stake at the time of the coin's confirmation
247 // (v0.2) nBits (deprecated): encodes all past block timestamps
248 // txPrev.block.nTime: prevent nodes from guessing a good timestamp to
249 // generate transaction for future advantage
250 // txPrev.offset: offset of txPrev inside block, to reduce the chance of
251 // nodes generating coinstake at the same time
252 // txPrev.nTime: reduce the chance of nodes generating coinstake at the same
254 // txPrev.vout.n: output number of txPrev, to reduce the chance of nodes
255 // generating coinstake at the same time
256 // block/tx hash should not be used here as they can be generated in vast
257 // quantities so as to generate blocks faster, degrading the system back into
258 // a proof-of-work situation.
260 bool CheckStakeKernelHash(unsigned int nBits, const CBlock& blockFrom, unsigned int nTxPrevOffset, const CTransaction& txPrev, const COutPoint& prevout, unsigned int nTimeTx, uint256& hashProofOfStake, bool fPrintProofOfStake)
262 if (nTimeTx < txPrev.nTime) // Transaction timestamp violation
263 return error("CheckStakeKernelHash() : nTime violation");
265 unsigned int nTimeBlockFrom = blockFrom.GetBlockTime();
266 if (nTimeBlockFrom + nStakeMinAge > nTimeTx) // Min age requirement
267 return error("CheckStakeKernelHash() : min age violation");
269 CBigNum bnTargetPerCoinDay;
270 bnTargetPerCoinDay.SetCompact(nBits);
271 int64 nValueIn = txPrev.vout[prevout.n].nValue;
273 // v0.3 protocol kernel hash weight starts from 0 at the 30-day min age
274 // this change increases active coins participating the hash and helps
275 // to secure the network when proof-of-stake difficulty is low
276 int64 nTimeWeight = min((int64)nTimeTx - txPrev.nTime, (int64)STAKE_MAX_AGE) - nStakeMinAge;
277 CBigNum bnCoinDayWeight = CBigNum(nValueIn) * nTimeWeight / COIN / (24 * 60 * 60);
280 CDataStream ss(SER_GETHASH, 0);
281 uint64 nStakeModifier = 0;
282 int nStakeModifierHeight = 0;
283 int64 nStakeModifierTime = 0;
285 if (!GetKernelStakeModifier(blockFrom.GetHash(), nStakeModifier, nStakeModifierHeight, nStakeModifierTime, fPrintProofOfStake))
287 ss << nStakeModifier;
289 ss << nTimeBlockFrom << nTxPrevOffset << txPrev.nTime << prevout.n << nTimeTx;
290 hashProofOfStake = Hash(ss.begin(), ss.end());
291 if (fPrintProofOfStake)
293 printf("CheckStakeKernelHash() : using modifier 0x%016"PRI64x" at height=%d timestamp=%s for block from height=%d timestamp=%s\n",
294 nStakeModifier, nStakeModifierHeight,
295 DateTimeStrFormat(nStakeModifierTime).c_str(),
296 mapBlockIndex[blockFrom.GetHash()]->nHeight,
297 DateTimeStrFormat(blockFrom.GetBlockTime()).c_str());
298 printf("CheckStakeKernelHash() : check protocol=%s modifier=0x%016"PRI64x" nTimeBlockFrom=%u nTxPrevOffset=%u nTimeTxPrev=%u nPrevout=%u nTimeTx=%u hashProof=%s\n",
301 nTimeBlockFrom, nTxPrevOffset, txPrev.nTime, prevout.n, nTimeTx,
302 hashProofOfStake.ToString().c_str());
305 // Now check if proof-of-stake hash meets target protocol
306 if (CBigNum(hashProofOfStake) > bnCoinDayWeight * bnTargetPerCoinDay)
308 if (fDebug && !fPrintProofOfStake)
310 printf("CheckStakeKernelHash() : using modifier 0x%016"PRI64x" at height=%d timestamp=%s for block from height=%d timestamp=%s\n",
311 nStakeModifier, nStakeModifierHeight,
312 DateTimeStrFormat(nStakeModifierTime).c_str(),
313 mapBlockIndex[blockFrom.GetHash()]->nHeight,
314 DateTimeStrFormat(blockFrom.GetBlockTime()).c_str());
315 printf("CheckStakeKernelHash() : pass protocol=%s modifier=0x%016"PRI64x" nTimeBlockFrom=%u nTxPrevOffset=%u nTimeTxPrev=%u nPrevout=%u nTimeTx=%u hashProof=%s\n",
318 nTimeBlockFrom, nTxPrevOffset, txPrev.nTime, prevout.n, nTimeTx,
319 hashProofOfStake.ToString().c_str());
324 // Check kernel hash target and coinstake signature
325 bool CheckProofOfStake(const CTransaction& tx, unsigned int nBits, uint256& hashProofOfStake)
327 if (!tx.IsCoinStake())
328 return error("CheckProofOfStake() : called on non-coinstake %s", tx.GetHash().ToString().c_str());
330 // Kernel (input 0) must match the stake hash target per coin age (nBits)
331 const CTxIn& txin = tx.vin[0];
333 // First try finding the previous transaction in database
337 if (!txPrev.ReadFromDisk(txdb, txin.prevout, txindex))
338 return tx.DoS(1, error("CheckProofOfStake() : INFO: read txPrev failed")); // previous transaction not in main chain, may occur during initial download
342 if (!VerifySignature(txPrev, tx, 0, true, 0))
343 return tx.DoS(100, error("CheckProofOfStake() : VerifySignature failed on coinstake %s", tx.GetHash().ToString().c_str()));
347 if (!block.ReadFromDisk(txindex.pos.nFile, txindex.pos.nBlockPos, false))
348 return fDebug? error("CheckProofOfStake() : read block failed") : false; // unable to read block of previous transaction
350 if (!CheckStakeKernelHash(nBits, block, txindex.pos.nTxPos - txindex.pos.nBlockPos, txPrev, txin.prevout, tx.nTime, hashProofOfStake, fDebug))
351 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
356 // Check whether the coinstake timestamp meets protocol
357 bool CheckCoinStakeTimestamp(int64 nTimeBlock, int64 nTimeTx)
360 return (nTimeBlock == nTimeTx);
363 // Get stake modifier checksum
364 unsigned int GetStakeModifierChecksum(const CBlockIndex* pindex)
366 assert (pindex->pprev || pindex->GetBlockHash() == hashGenesisBlock);
367 // Hash previous checksum with flags, hashProofOfStake and nStakeModifier
368 CDataStream ss(SER_GETHASH, 0);
370 ss << pindex->pprev->nStakeModifierChecksum;
371 ss << pindex->nFlags << pindex->hashProofOfStake << pindex->nStakeModifier;
372 uint256 hashChecksum = Hash(ss.begin(), ss.end());
373 hashChecksum >>= (256 - 32);
374 return hashChecksum.Get64();
377 // Check stake modifier hard checkpoints
378 bool CheckStakeModifierCheckpoints(int nHeight, unsigned int nStakeModifierChecksum)
380 if (fTestNet) return true; // Testnet has no checkpoints
381 if (mapStakeModifierCheckpoints.count(nHeight))
382 return nStakeModifierChecksum == mapStakeModifierCheckpoints[nHeight];