aboutsummaryrefslogtreecommitdiff
path: root/src/merkleblock.cpp
blob: f9006d46d5989508752e4640d737ed5a36fd3db8 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
// Copyright (c) 2009-2010 Satoshi Nakamoto
// Copyright (c) 2009-2014 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.

#include "merkleblock.h"

#include "hash.h"
#include "primitives/block.h" // for MAX_BLOCK_SIZE
#include "utilstrencodings.h"

using namespace std;

CMerkleBlock::CMerkleBlock(const CBlock& block, CBloomFilter& filter)
{
    header = block.GetBlockHeader();

    vector<bool> vMatch;
    vector<uint256> vHashes;

    vMatch.reserve(block.vtx.size());
    vHashes.reserve(block.vtx.size());

    for (unsigned int i = 0; i < block.vtx.size(); i++)
    {
        const uint256& hash = block.vtx[i].GetHash();
        if (filter.IsRelevantAndUpdate(block.vtx[i]))
        {
            vMatch.push_back(true);
            vMatchedTxn.push_back(make_pair(i, hash));
        }
        else
            vMatch.push_back(false);
        vHashes.push_back(hash);
    }

    txn = CPartialMerkleTree(vHashes, vMatch);
}

uint256 CPartialMerkleTree::CalcHash(int height, unsigned int pos, const std::vector<uint256> &vTxid) {
    if (height == 0) {
        // hash at height 0 is the txids themself
        return vTxid[pos];
    } else {
        // calculate left hash
        uint256 left = CalcHash(height-1, pos*2, vTxid), right;
        // calculate right hash if not beyond the end of the array - copy left hash otherwise1
        if (pos*2+1 < CalcTreeWidth(height-1))
            right = CalcHash(height-1, pos*2+1, vTxid);
        else
            right = left;
        // combine subhashes
        return Hash(BEGIN(left), END(left), BEGIN(right), END(right));
    }
}

void CPartialMerkleTree::TraverseAndBuild(int height, unsigned int pos, const std::vector<uint256> &vTxid, const std::vector<bool> &vMatch) {
    // determine whether this node is the parent of at least one matched txid
    bool fParentOfMatch = false;
    for (unsigned int p = pos << height; p < (pos+1) << height && p < nTransactions; p++)
        fParentOfMatch |= vMatch[p];
    // store as flag bit
    vBits.push_back(fParentOfMatch);
    if (height==0 || !fParentOfMatch) {
        // if at height 0, or nothing interesting below, store hash and stop
        vHash.push_back(CalcHash(height, pos, vTxid));
    } else {
        // otherwise, don't store any hash, but descend into the subtrees
        TraverseAndBuild(height-1, pos*2, vTxid, vMatch);
        if (pos*2+1 < CalcTreeWidth(height-1))
            TraverseAndBuild(height-1, pos*2+1, vTxid, vMatch);
    }
}

uint256 CPartialMerkleTree::TraverseAndExtract(int height, unsigned int pos, unsigned int &nBitsUsed, unsigned int &nHashUsed, std::vector<uint256> &vMatch) {
    if (nBitsUsed >= vBits.size()) {
        // overflowed the bits array - failure
        fBad = true;
        return 0;
    }
    bool fParentOfMatch = vBits[nBitsUsed++];
    if (height==0 || !fParentOfMatch) {
        // if at height 0, or nothing interesting below, use stored hash and do not descend
        if (nHashUsed >= vHash.size()) {
            // overflowed the hash array - failure
            fBad = true;
            return 0;
        }
        const uint256 &hash = vHash[nHashUsed++];
        if (height==0 && fParentOfMatch) // in case of height 0, we have a matched txid
            vMatch.push_back(hash);
        return hash;
    } else {
        // otherwise, descend into the subtrees to extract matched txids and hashes
        uint256 left = TraverseAndExtract(height-1, pos*2, nBitsUsed, nHashUsed, vMatch), right;
        if (pos*2+1 < CalcTreeWidth(height-1)) {
            right = TraverseAndExtract(height-1, pos*2+1, nBitsUsed, nHashUsed, vMatch);
            if (right == left) {
                // If the left and right branch should never be identical as the transaction
                // hashes covered by them must be unique.
                fBad = true;
            }
        } else {
            right = left;
        }
        // and combine them before returning
        return Hash(BEGIN(left), END(left), BEGIN(right), END(right));
    }
}

CPartialMerkleTree::CPartialMerkleTree(const std::vector<uint256> &vTxid, const std::vector<bool> &vMatch) : nTransactions(vTxid.size()), fBad(false) {
    // reset state
    vBits.clear();
    vHash.clear();

    // calculate height of tree
    int nHeight = 0;
    while (CalcTreeWidth(nHeight) > 1)
        nHeight++;

    // traverse the partial tree
    TraverseAndBuild(nHeight, 0, vTxid, vMatch);
}

CPartialMerkleTree::CPartialMerkleTree() : nTransactions(0), fBad(true) {}

uint256 CPartialMerkleTree::ExtractMatches(std::vector<uint256> &vMatch) {
    vMatch.clear();
    // An empty set will not work
    if (nTransactions == 0)
        return 0;
    // check for excessively high numbers of transactions
    if (nTransactions > MAX_BLOCK_SIZE / 60) // 60 is the lower bound for the size of a serialized CTransaction
        return 0;
    // there can never be more hashes provided than one for every txid
    if (vHash.size() > nTransactions)
        return 0;
    // there must be at least one bit per node in the partial tree, and at least one node per hash
    if (vBits.size() < vHash.size())
        return 0;
    // calculate height of tree
    int nHeight = 0;
    while (CalcTreeWidth(nHeight) > 1)
        nHeight++;
    // traverse the partial tree
    unsigned int nBitsUsed = 0, nHashUsed = 0;
    uint256 hashMerkleRoot = TraverseAndExtract(nHeight, 0, nBitsUsed, nHashUsed, vMatch);
    // verify that no problems occured during the tree traversal
    if (fBad)
        return 0;
    // verify that all bits were consumed (except for the padding caused by serializing it as a byte sequence)
    if ((nBitsUsed+7)/8 != (vBits.size()+7)/8)
        return 0;
    // verify that all hashes were consumed
    if (nHashUsed != vHash.size())
        return 0;
    return hashMerkleRoot;
}