// find last block index up to index
public static ChainedBlock GetLastBlockIndex(StakeChain stakeChain, ChainedBlock index, bool proofOfStake)
{
if (index == null)
{
throw new ArgumentNullException(nameof(index));
}
var blockStake = stakeChain.Get(index.HashBlock);
while (index.Previous != null && (blockStake.IsProofOfStake() != proofOfStake))
{
index = index.Previous;
blockStake = stakeChain.Get(index.HashBlock);
}
return(index);
}
/// <summary>
/// Check PoW and that the blocks connect correctly
/// </summary>
/// <param name="network">The network being used</param>
/// <returns>True if PoW is correct</returns>
public static bool Validate(Network network, ChainedBlock chainedBlock, StakeChain stakeChain = null)
{
if (network == null)
{
throw new ArgumentNullException("network");
}
if (chainedBlock.Height != 0 && chainedBlock.Previous == null)
{
return(false);
}
var heightCorrect = chainedBlock.Height == 0 || chainedBlock.Height == chainedBlock.Previous.Height + 1;
var genesisCorrect = chainedBlock.Height != 0 || chainedBlock.HashBlock == network.GetGenesis().GetHash();
var hashPrevCorrect = chainedBlock.Height == 0 || chainedBlock.Header.HashPrevBlock == chainedBlock.Previous.HashBlock;
var hashCorrect = chainedBlock.HashBlock == chainedBlock.Header.GetHash();
if (stakeChain == null)
{
return(heightCorrect && genesisCorrect && hashPrevCorrect && hashCorrect);
}
var workCorrect = stakeChain.CheckPowPosAndTarget(chainedBlock, stakeChain.Get(chainedBlock.HashBlock), network);
return(heightCorrect && genesisCorrect && hashPrevCorrect && hashCorrect && workCorrect);
}
// 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.
private static bool ComputeNextStakeModifier(StakeChain stakeChain, ChainBase chainIndex, ChainedBlock pindexPrev, out ulong nStakeModifier,
out bool fGeneratedStakeModifier)
{
nStakeModifier = 0;
fGeneratedStakeModifier = false;
if (pindexPrev == null)
{
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
long nModifierTime = 0;
if (!GetLastStakeModifier(stakeChain, pindexPrev, out nStakeModifier, out nModifierTime))
{
return(false); //error("ComputeNextStakeModifier: unable to get last modifier");
}
//LogPrint("stakemodifier", "ComputeNextStakeModifier: prev modifier=0x%016x time=%s\n", nStakeModifier, DateTimeStrFormat(nModifierTime));
if (nModifierTime / ModifierInterval >= pindexPrev.Header.Time / ModifierInterval)
{
return(true);
}
// Sort candidate blocks by timestamp
var sortedByTimestamp = new SortedDictionary <uint, uint256>();
long nSelectionInterval = GetStakeModifierSelectionInterval();
long nSelectionIntervalStart = (pindexPrev.Header.Time / ModifierInterval) * ModifierInterval - nSelectionInterval;
var pindex = pindexPrev;
while (pindex != null && pindex.Header.Time >= nSelectionIntervalStart)
{
sortedByTimestamp.Add(pindex.Header.Time, pindex.HashBlock);
pindex = pindex.Previous;
}
int nHeightFirstCandidate = pindex?.Height + 1 ?? 0;
// Select 64 blocks from candidate blocks to generate stake modifier
ulong nStakeModifierNew = 0;
long nSelectionIntervalStop = nSelectionIntervalStart;
var mapSelectedBlocks = new Dictionary <uint256, ChainedBlock>();
for (int nRound = 0; nRound < Math.Min(64, sortedByTimestamp.Count); nRound++)
{
// add an interval section to the current selection round
nSelectionIntervalStop += GetStakeModifierSelectionIntervalSection(nRound);
// select a block from the candidates of current round
if (!SelectBlockFromCandidates(stakeChain, pindexPrev, sortedByTimestamp, mapSelectedBlocks, nSelectionIntervalStop, nStakeModifier, out pindex))
{
return(false); // error("ComputeNextStakeModifier: unable to select block at round %d", nRound);
}
// write the entropy bit of the selected block
var blockStake = stakeChain.Get(pindex.HashBlock);
nStakeModifierNew |= ((ulong)blockStake.GetStakeEntropyBit() << nRound);
// add the selected block from candidates to selected list
mapSelectedBlocks.Add(pindex.HashBlock, 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);
}
// select a block from the candidate blocks in vSortedByTimestamp, excluding
// already selected blocks in vSelectedBlocks, and with timestamp up to
// nSelectionIntervalStop.
private static bool SelectBlockFromCandidates(StakeChain stakeChain, ChainedBlock chainIndex, SortedDictionary <uint, uint256> sortedByTimestamp,
Dictionary <uint256, ChainedBlock> mapSelectedBlocks,
long nSelectionIntervalStop, ulong nStakeModifierPrev, out ChainedBlock pindexSelected)
{
bool fSelected = false;
uint256 hashBest = 0;
pindexSelected = null;
foreach (var item in sortedByTimestamp)
{
var pindex = chainIndex.FindAncestorOrSelf(item.Value);
if (pindex == null)
{
return(false); // error("SelectBlockFromCandidates: failed to find block index for candidate block %s", item.second.ToString());
}
if (fSelected && pindex.Header.Time > nSelectionIntervalStop)
{
break;
}
if (mapSelectedBlocks.Keys.Any(key => key == pindex.HashBlock))
{
continue;
}
var blockStake = stakeChain.Get(pindex.HashBlock);
// compute the selection hash by hashing its proof-hash and the
// previous proof-of-stake modifier
uint256 hashSelection;
using (var ms = new MemoryStream())
{
var serializer = new BitcoinStream(ms, true);
serializer.ReadWrite(blockStake.HashProof);
serializer.ReadWrite(nStakeModifierPrev);
hashSelection = Hashes.Hash256(ms.ToArray());
}
// 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 (blockStake.IsProofOfStake())
{
hashSelection >>= 32;
}
if (fSelected && hashSelection < hashBest)
{
hashBest = hashSelection;
pindexSelected = pindex;
}
else if (!fSelected)
{
fSelected = true;
hashBest = hashSelection;
pindexSelected = pindex;
}
}
//LogPrint("stakemodifier", "SelectBlockFromCandidates: selection hash=%s\n", hashBest.ToString());
return(fSelected);
}
public static bool ComputeStakeModifier(ChainBase chainIndex, ChainedBlock pindex, BlockStake blockStake, StakeChain stakeChain)
{
var pindexPrev = pindex.Previous;
var blockStakePrev = pindexPrev == null ? null : stakeChain.Get(pindexPrev.HashBlock);
// compute stake modifier
ulong nStakeModifier;
bool fGeneratedStakeModifier;
if (!ComputeNextStakeModifier(stakeChain, chainIndex, pindexPrev, out nStakeModifier, out fGeneratedStakeModifier))
{
return(false); //error("AddToBlockIndex() : ComputeNextStakeModifier() failed");
}
blockStake.SetStakeModifier(nStakeModifier, fGeneratedStakeModifier);
blockStake.StakeModifierV2 = ComputeStakeModifierV2(
pindexPrev, blockStakePrev, blockStake.IsProofOfWork() ? pindex.HashBlock : blockStake.PrevoutStake.Hash);
return(true);
}
public const uint ModifierInterval = 10 * 60; // time to elapse before new modifier is computed
public static bool CheckAndComputeStake(IBlockRepository blockStore, ITransactionRepository trasnactionStore, IBlockTransactionMapStore mapStore, StakeChain stakeChain,
ChainBase chainIndex, ChainedBlock pindex, Block block, out BlockStake blockStake)
{
if (block.GetHash() != pindex.HashBlock)
{
throw new ArgumentException();
}
blockStake = new BlockStake(block);
uint256 hashProof = null;
// Verify hash target and signature of coinstake tx
if (BlockStake.IsProofOfStake(block))
{
var pindexPrev = pindex.Previous;
var prevBlockStake = stakeChain.Get(pindexPrev.HashBlock);
if (prevBlockStake == null)
{
return(false); // the stake proof of the previous block is not set
}
uint256 targetProofOfStake;
if (!CheckProofOfStake(blockStore, trasnactionStore, mapStore, pindexPrev, prevBlockStake, block.Transactions[1],
pindex.Header.Bits.ToCompact(), out hashProof, out targetProofOfStake))
{
return(false); // error("AcceptBlock() : check proof-of-stake failed for block %s", hash.ToString());
}
}
// PoW is checked in CheckBlock()
if (BlockStake.IsProofOfWork(block))
{
hashProof = pindex.Header.GetPoWHash();
}
// todo: is this the same as chain work?
// compute chain trust score
//pindexNew.nChainTrust = (pindexNew->pprev ? pindexNew->pprev->nChainTrust : 0) + pindexNew->GetBlockTrust();
// compute stake entropy bit for stake modifier
if (!blockStake.SetStakeEntropyBit(blockStake.GetStakeEntropyBit()))
{
return(false); //error("AddToBlockIndex() : SetStakeEntropyBit() failed");
}
// Record proof hash value
blockStake.HashProof = hashProof;
// compute stake modifier
return(ComputeStakeModifier(chainIndex, pindex, blockStake, stakeChain));
}
public static Target GetNextTargetRequired(StakeChain stakeChain, ChainedBlock indexLast, Consensus consensus, bool proofOfStake)
{
// Genesis block
if (indexLast == null)
{
return(consensus.PowLimit);
}
// find the last two blocks that correspond to the mining algo
// (i.e if this is a POS block we need to find the last two POS blocks)
var targetLimit = proofOfStake
? GetProofOfStakeLimit(consensus, indexLast.Height)
: consensus.PowLimit.ToBigInteger();
// first block
var pindexPrev = GetLastBlockIndex(stakeChain, indexLast, proofOfStake);
if (pindexPrev.Previous == null)
{
return(new Target(targetLimit));
}
// second block
var pindexPrevPrev = GetLastBlockIndex(stakeChain, pindexPrev.Previous, proofOfStake);
if (pindexPrevPrev.Previous == null)
{
return(new Target(targetLimit));
}
int targetSpacing = GetTargetSpacing(indexLast.Height);
int actualSpacing = (int)(pindexPrev.Header.Time - pindexPrevPrev.Header.Time);
if (IsProtocolV1RetargetingFixed(indexLast.Height))
{
if (actualSpacing < 0)
{
actualSpacing = targetSpacing;
}
}
if (IsProtocolV3((int)indexLast.Header.Time))
{
if (actualSpacing > targetSpacing * 10)
{
actualSpacing = targetSpacing * 10;
}
}
// target change every block
// retarget with exponential moving toward target spacing
var targetTimespan = 16 * 60; // 16 mins
var target = pindexPrev.Header.Bits.ToBigInteger();
int interval = targetTimespan / targetSpacing;
target = target.Multiply(BigInteger.ValueOf(((interval - 1) * targetSpacing + actualSpacing + actualSpacing)));
target = target.Divide(BigInteger.ValueOf(((interval + 1) * targetSpacing)));
if (target.CompareTo(BigInteger.Zero) <= 0 || target.CompareTo(targetLimit) >= 1)
{
//if (target <= 0 || target > targetLimit)
target = targetLimit;
}
return(new Target(target));
}
