src/merkleblock.cpp

   1 // Copyright (c) 2009-2010 Satoshi Nakamoto
   2 // Copyright (c) 2009-2016 The Bitcoin Core developers
   3 // Distributed under the MIT software license, see the accompanying
   4 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
   5
   6 #include "merkleblock.h"
   7
   8 #include "hash.h"
   9 #include "consensus/consensus.h"
  10 #include "utilstrencodings.h"
  11
  12 CMerkleBlock::CMerkleBlock(const CBlock& block, CBloomFilter& filter)
  13 {
  14     header = block.GetBlockHeader();
  15
  16     std::vector<bool> vMatch;
  17     std::vector<uint256> vHashes;
  18
  19     vMatch.reserve(block.vtx.size());
  20     vHashes.reserve(block.vtx.size());
  21
  22     for (unsigned int i = 0; i < block.vtx.size(); i++)
  23     {
  24         const uint256& hash = block.vtx[i]->GetHash();
  25         if (filter.IsRelevantAndUpdate(*block.vtx[i]))
  26         {
  27             vMatch.push_back(true);
  28             vMatchedTxn.push_back(std::make_pair(i, hash));
  29         }
  30         else
  31             vMatch.push_back(false);
  32         vHashes.push_back(hash);
  33     }
  34
  35     txn = CPartialMerkleTree(vHashes, vMatch);
  36 }
  37
  38 CMerkleBlock::CMerkleBlock(const CBlock& block, const std::set<uint256>& txids)
  39 {
  40     header = block.GetBlockHeader();
  41
  42     std::vector<bool> vMatch;
  43     std::vector<uint256> vHashes;
  44
  45     vMatch.reserve(block.vtx.size());
  46     vHashes.reserve(block.vtx.size());
  47
  48     for (unsigned int i = 0; i < block.vtx.size(); i++)
  49     {
  50         const uint256& hash = block.vtx[i]->GetHash();
  51         if (txids.count(hash))
  52             vMatch.push_back(true);
  53         else
  54             vMatch.push_back(false);
  55         vHashes.push_back(hash);
  56     }
  57
  58     txn = CPartialMerkleTree(vHashes, vMatch);
  59 }
  60
  61 uint256 CPartialMerkleTree::CalcHash(int height, unsigned int pos, const std::vector<uint256> &vTxid) {
  62     if (height == 0) {
  63         // hash at height 0 is the txids themself
  64         return vTxid[pos];
  65     } else {
  66         // calculate left hash
  67         uint256 left = CalcHash(height-1, pos*2, vTxid), right;
  68         // calculate right hash if not beyond the end of the array - copy left hash otherwise1
  69         if (pos*2+1 < CalcTreeWidth(height-1))
  70             right = CalcHash(height-1, pos*2+1, vTxid);
  71         else
  72             right = left;
  73         // combine subhashes
  74         return Hash(BEGIN(left), END(left), BEGIN(right), END(right));
  75     }
  76 }
  77
  78 void CPartialMerkleTree::TraverseAndBuild(int height, unsigned int pos, const std::vector<uint256> &vTxid, const std::vector<bool> &vMatch) {
  79     // determine whether this node is the parent of at least one matched txid
  80     bool fParentOfMatch = false;
  81     for (unsigned int p = pos << height; p < (pos+1) << height && p < nTransactions; p++)
  82         fParentOfMatch |= vMatch[p];
  83     // store as flag bit
  84     vBits.push_back(fParentOfMatch);
  85     if (height==0 || !fParentOfMatch) {
  86         // if at height 0, or nothing interesting below, store hash and stop
  87         vHash.push_back(CalcHash(height, pos, vTxid));
  88     } else {
  89         // otherwise, don't store any hash, but descend into the subtrees
  90         TraverseAndBuild(height-1, pos*2, vTxid, vMatch);
  91         if (pos*2+1 < CalcTreeWidth(height-1))
  92             TraverseAndBuild(height-1, pos*2+1, vTxid, vMatch);
  93     }
  94 }
  95
  96 uint256 CPartialMerkleTree::TraverseAndExtract(int height, unsigned int pos, unsigned int &nBitsUsed, unsigned int &nHashUsed, std::vector<uint256> &vMatch, std::vector<unsigned int> &vnIndex) {
  97     if (nBitsUsed >= vBits.size()) {
  98         // overflowed the bits array - failure
  99         fBad = true;
 100         return uint256();
 101     }
 102     bool fParentOfMatch = vBits[nBitsUsed++];
 103     if (height==0 || !fParentOfMatch) {
 104         // if at height 0, or nothing interesting below, use stored hash and do not descend
 105         if (nHashUsed >= vHash.size()) {
 106             // overflowed the hash array - failure
 107             fBad = true;
 108             return uint256();
 109         }
 110         const uint256 &hash = vHash[nHashUsed++];
 111         if (height==0 && fParentOfMatch) { // in case of height 0, we have a matched txid
 112             vMatch.push_back(hash);
 113             vnIndex.push_back(pos);
 114         }
 115         return hash;
 116     } else {
 117         // otherwise, descend into the subtrees to extract matched txids and hashes
 118         uint256 left = TraverseAndExtract(height-1, pos*2, nBitsUsed, nHashUsed, vMatch, vnIndex), right;
 119         if (pos*2+1 < CalcTreeWidth(height-1)) {
 120             right = TraverseAndExtract(height-1, pos*2+1, nBitsUsed, nHashUsed, vMatch, vnIndex);
 121             if (right == left) {
 122                 // The left and right branches should never be identical, as the transaction
 123                 // hashes covered by them must each be unique.
 124                 fBad = true;
 125             }
 126         } else {
 127             right = left;
 128         }
 129         // and combine them before returning
 130         return Hash(BEGIN(left), END(left), BEGIN(right), END(right));
 131     }
 132 }
 133
 134 CPartialMerkleTree::CPartialMerkleTree(const std::vector<uint256> &vTxid, const std::vector<bool> &vMatch) : nTransactions(vTxid.size()), fBad(false) {
 135     // reset state
 136     vBits.clear();
 137     vHash.clear();
 138
 139     // calculate height of tree
 140     int nHeight = 0;
 141     while (CalcTreeWidth(nHeight) > 1)
 142         nHeight++;
 143
 144     // traverse the partial tree
 145     TraverseAndBuild(nHeight, 0, vTxid, vMatch);
 146 }
 147
 148 CPartialMerkleTree::CPartialMerkleTree() : nTransactions(0), fBad(true) {}
 149
 150 uint256 CPartialMerkleTree::ExtractMatches(std::vector<uint256> &vMatch, std::vector<unsigned int> &vnIndex) {
 151     vMatch.clear();
 152     // An empty set will not work
 153     if (nTransactions == 0)
 154         return uint256();
 155     // check for excessively high numbers of transactions
 156     if (nTransactions > MAX_BLOCK_BASE_SIZE / 60) // 60 is the lower bound for the size of a serialized CTransaction
 157         return uint256();
 158     // there can never be more hashes provided than one for every txid
 159     if (vHash.size() > nTransactions)
 160         return uint256();
 161     // there must be at least one bit per node in the partial tree, and at least one node per hash
 162     if (vBits.size() < vHash.size())
 163         return uint256();
 164     // calculate height of tree
 165     int nHeight = 0;
 166     while (CalcTreeWidth(nHeight) > 1)
 167         nHeight++;
 168     // traverse the partial tree
 169     unsigned int nBitsUsed = 0, nHashUsed = 0;
 170     uint256 hashMerkleRoot = TraverseAndExtract(nHeight, 0, nBitsUsed, nHashUsed, vMatch, vnIndex);
 171     // verify that no problems occurred during the tree traversal
 172     if (fBad)
 173         return uint256();
 174     // verify that all bits were consumed (except for the padding caused by serializing it as a byte sequence)
 175     if ((nBitsUsed+7)/8 != (vBits.size()+7)/8)
 176         return uint256();
 177     // verify that all hashes were consumed
 178     if (nHashUsed != vHash.size())
 179         return uint256();
 180     return hashMerkleRoot;
 181 }