stakemodifier.cpp

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// Copyright (c) 2011-2013 The PPCoin developers
// Copyright (c) 2013-2014 The NovaCoin Developers
// Copyright (c) 2014-2018 The BlackCoin Developers
// Copyright (c) 2015-2021 The PIVX Core developers
// Distributed under the MIT/X11 software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
#include "legacy/stakemodifier.h"
#include "validation.h"   // mapBlockIndex, chainActive
 
/*
 * Old Modifier - Only for IBD
 */
 
static const unsigned int MODIFIER_INTERVAL = 60;
static const int MODIFIER_INTERVAL_RATIO = 3;
static const int64_t OLD_MODIFIER_INTERVAL = 2087;
 
// Get selection interval section (in seconds)
static int64_t GetStakeModifierSelectionIntervalSection(int nSection)
{
    assert(nSection >= 0 && nSection < 64);
    int64_t a = MODIFIER_INTERVAL  * 63 / (63 + ((63 - nSection) * (MODIFIER_INTERVAL_RATIO - 1)));
    return a;
}
 
// select a block from the candidate blocks in vSortedByTimestamp, excluding
// already selected blocks in vSelectedBlocks, and with timestamp up to
// nSelectionIntervalStop.
static bool SelectBlockFromCandidates(
    std::vector<std::pair<int64_t, uint256> >& vSortedByTimestamp,
    std::map<uint256, const CBlockIndex*>& mapSelectedBlocks,
    int64_t nSelectionIntervalStop,
    uint64_t nStakeModifierPrev,
    const CBlockIndex** pindexSelected)
{
    bool fModifierV2 = false;
    bool fFirstRun = true;
    bool fSelected = false;
    arith_uint256 hashBest = ARITH_UINT256_ZERO;
    *pindexSelected = (const CBlockIndex*)0;
    for (const auto& item : vSortedByTimestamp) {
        if (!mapBlockIndex.count(item.second))
            return error("%s : failed to find block index for candidate block %s", __func__, item.second.ToString().c_str());
 
        const CBlockIndex* pindex = mapBlockIndex[item.second];
        if (fSelected && pindex->GetBlockTime() > nSelectionIntervalStop)
            break;
 
        //if the lowest block height (vSortedByTimestamp[0]) is >= switch height, use new modifier calc
        if (fFirstRun){
            fModifierV2 = Params().GetConsensus().NetworkUpgradeActive(pindex->nHeight, Consensus::UPGRADE_POS_V2);
            fFirstRun = false;
        }
 
        if (mapSelectedBlocks.count(pindex->GetBlockHash()) > 0)
            continue;
 
        // compute the selection hash by hashing an input that is unique to that block
        uint256 hashProof;
        if(fModifierV2)
            hashProof = pindex->GetBlockHash();
        else
            hashProof = pindex->IsProofOfStake() ? UINT256_ZERO : pindex->GetBlockHash();
 
        CDataStream ss(SER_GETHASH, 0);
        ss << hashProof << nStakeModifierPrev;
        arith_uint256 hashSelection = UintToArith256(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;
        }
    }
    return fSelected;
}
 
// 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
bool GetOldModifier(const CBlockIndex* pindexFrom, uint64_t& nStakeModifier)
{
    int64_t nStakeModifierTime = pindexFrom->GetBlockTime();
    const CBlockIndex* pindex = pindexFrom;
    CBlockIndex* pindexNext = chainActive[pindex->nHeight + 1];
 
    // loop to find the stake modifier later by a selection interval
    do {
        if (!pindexNext) {
            // Should never happen
            return error("%s : Null pindexNext, current block %s ", __func__, pindex->phashBlock->GetHex());
        }
        pindex = pindexNext;
        if (pindex->GeneratedStakeModifier()) nStakeModifierTime = pindex->GetBlockTime();
        pindexNext = chainActive[pindex->nHeight + 1];
    } while (nStakeModifierTime < pindexFrom->GetBlockTime() + OLD_MODIFIER_INTERVAL);
 
    nStakeModifier = pindex->GetStakeModifierV1();
    return true;
}
 
bool GetOldStakeModifier(CStakeInput* stake, uint64_t& nStakeModifier)
{
    const CBlockIndex* pindexFrom = stake->GetIndexFrom();
    if (!pindexFrom) return error("%s : failed to get index from", __func__);
    if (stake->IsZPIV()) {
        int64_t nTimeBlockFrom = pindexFrom->GetBlockTime();
        const int nHeightStop = std::min(chainActive.Height(), Params().GetConsensus().height_last_ZC_AccumCheckpoint-1);
        while (pindexFrom && pindexFrom->nHeight + 1 <= nHeightStop) {
            if (pindexFrom->GetBlockTime() - nTimeBlockFrom > 60 * 60) {
                nStakeModifier = pindexFrom->nAccumulatorCheckpoint.GetCheapHash();
                return true;
            }
            pindexFrom = chainActive.Next(pindexFrom);
        }
        return false;
 
    } else if (!GetOldModifier(pindexFrom, nStakeModifier))
        return error("%s : failed to get kernel stake modifier", __func__);
 
    return true;
}
 
// sort blocks by timestamp, soliving tie with hash (taken as arith_uint)
static bool sortedByTimestamp(const std::pair<uint64_t, uint256>& a,
                              const std::pair<uint64_t, uint256>& b)
{
    if (a.first == b.first) {
        return UintToArith256(a.second) < UintToArith256(b.second);
    }
    return a.first < b.first;
}
 
// 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
    }
    if (pindexPrev->nHeight == 0) {
        //Give a stake modifier to the first block
        fGeneratedStakeModifier = true;
        nStakeModifier = uint64_t("stakemodifier");
        return true;
    }
 
    // 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;
    const CBlockIndex* p = pindexPrev;
    while (p && p->pprev && !p->GeneratedStakeModifier()) p = p->pprev;
    if (!p->GeneratedStakeModifier()) return error("%s : unable to get last modifier", __func__);
    nStakeModifier = p->GetStakeModifierV1();
    nModifierTime = p->GetBlockTime();
 
    if (nModifierTime / MODIFIER_INTERVAL >= pindexPrev->GetBlockTime() / MODIFIER_INTERVAL)
        return true;
 
    // Sort candidate blocks by timestamp
    std::vector<std::pair<int64_t, uint256> > vSortedByTimestamp;
    vSortedByTimestamp.reserve(64 * MODIFIER_INTERVAL  / Params().GetConsensus().nTargetSpacing);
    int64_t nSelectionIntervalStart = (pindexPrev->GetBlockTime() / MODIFIER_INTERVAL ) * MODIFIER_INTERVAL  - OLD_MODIFIER_INTERVAL;
    const CBlockIndex* pindex = pindexPrev;
 
    while (pindex && pindex->GetBlockTime() >= nSelectionIntervalStart) {
        vSortedByTimestamp.emplace_back(pindex->GetBlockTime(), pindex->GetBlockHash());
        pindex = pindex->pprev;
    }
 
    std::reverse(vSortedByTimestamp.begin(), vSortedByTimestamp.end());
    std::sort(vSortedByTimestamp.begin(), vSortedByTimestamp.end(), sortedByTimestamp);
 
    // Select 64 blocks from candidate blocks to generate stake modifier
    uint64_t nStakeModifierNew = 0;
    int64_t nSelectionIntervalStop = nSelectionIntervalStart;
    std::map<uint256, const CBlockIndex*> mapSelectedBlocks;
    for (int nRound = 0; nRound < std::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("%s : unable to select block at round %d", __func__, 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.emplace(pindex->GetBlockHash(), pindex);
    }
 
    nStakeModifier = nStakeModifierNew;
    fGeneratedStakeModifier = true;
    return true;
}