254 lines
10 KiB
C++
254 lines
10 KiB
C++
// Copyright (c) 2015 The Bitcoin Core developers
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// Distributed under the MIT software license, see the accompanying
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// file COPYING or http://www.opensource.org/licenses/mit-license.php.
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#include "consensus/merkle.h"
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#include "test/test_bitcoin.h"
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#include "util/strencodings.h"
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#include <boost/test/unit_test.hpp>
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BOOST_FIXTURE_TEST_SUITE(merkle_tests, TestingSetup)
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static uint256 ComputeMerkleRootFromBranch(const uint256& leaf, const std::vector<uint256>& vMerkleBranch, uint32_t nIndex) {
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uint256 hash = leaf;
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for (std::vector<uint256>::const_iterator it = vMerkleBranch.begin(); it != vMerkleBranch.end(); ++it) {
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if (nIndex & 1) {
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hash = Hash(BEGIN(*it), END(*it), BEGIN(hash), END(hash));
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} else {
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hash = Hash(BEGIN(hash), END(hash), BEGIN(*it), END(*it));
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}
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nIndex >>= 1;
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}
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return hash;
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}
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/* This implements a constant-space merkle root/path calculator, limited to 2^32 leaves. */
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static void MerkleComputation(const std::vector<uint256>& leaves, uint256* proot, bool* pmutated, uint32_t branchpos, std::vector<uint256>* pbranch) {
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if (pbranch) pbranch->clear();
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if (leaves.size() == 0) {
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if (pmutated) *pmutated = false;
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if (proot) *proot = uint256();
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return;
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}
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bool mutated = false;
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// count is the number of leaves processed so far.
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uint32_t count = 0;
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// inner is an array of eagerly computed subtree hashes, indexed by tree
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// level (0 being the leaves).
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// For example, when count is 25 (11001 in binary), inner[4] is the hash of
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// the first 16 leaves, inner[3] of the next 8 leaves, and inner[0] equal to
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// the last leaf. The other inner entries are undefined.
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uint256 inner[32];
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// Which position in inner is a hash that depends on the matching leaf.
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int matchlevel = -1;
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// First process all leaves into 'inner' values.
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while (count < leaves.size()) {
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uint256 h = leaves[count];
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bool matchh = count == branchpos;
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count++;
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int level;
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// For each of the lower bits in count that are 0, do 1 step. Each
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// corresponds to an inner value that existed before processing the
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// current leaf, and each needs a hash to combine it.
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for (level = 0; !(count & (((uint32_t)1) << level)); level++) {
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if (pbranch) {
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if (matchh) {
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pbranch->push_back(inner[level]);
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} else if (matchlevel == level) {
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pbranch->push_back(h);
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matchh = true;
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}
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}
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mutated |= (inner[level] == h);
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CHash256().Write(inner[level].begin(), 32).Write(h.begin(), 32).Finalize(h.begin());
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}
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// Store the resulting hash at inner position level.
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inner[level] = h;
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if (matchh) {
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matchlevel = level;
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}
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}
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// Do a final 'sweep' over the rightmost branch of the tree to process
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// odd levels, and reduce everything to a single top value.
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// Level is the level (counted from the bottom) up to which we've sweeped.
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int level = 0;
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// As long as bit number level in count is zero, skip it. It means there
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// is nothing left at this level.
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while (!(count & (((uint32_t)1) << level))) {
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level++;
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}
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uint256 h = inner[level];
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bool matchh = matchlevel == level;
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while (count != (((uint32_t)1) << level)) {
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// If we reach this point, h is an inner value that is not the top.
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// We combine it with itself (Bitcoin's special rule for odd levels in
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// the tree) to produce a higher level one.
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if (pbranch && matchh) {
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pbranch->push_back(h);
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}
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CHash256().Write(h.begin(), 32).Write(h.begin(), 32).Finalize(h.begin());
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// Increment count to the value it would have if two entries at this
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// level had existed.
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count += (((uint32_t)1) << level);
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level++;
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// And propagate the result upwards accordingly.
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while (!(count & (((uint32_t)1) << level))) {
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if (pbranch) {
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if (matchh) {
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pbranch->push_back(inner[level]);
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} else if (matchlevel == level) {
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pbranch->push_back(h);
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matchh = true;
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}
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}
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CHash256().Write(inner[level].begin(), 32).Write(h.begin(), 32).Finalize(h.begin());
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level++;
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}
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}
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// Return result.
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if (pmutated) *pmutated = mutated;
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if (proot) *proot = h;
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}
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static std::vector<uint256> ComputeMerkleBranch(const std::vector<uint256>& leaves, uint32_t position) {
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std::vector<uint256> ret;
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MerkleComputation(leaves, nullptr, nullptr, position, &ret);
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return ret;
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}
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static std::vector<uint256> BlockMerkleBranch(const CBlock& block, uint32_t position)
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{
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std::vector<uint256> leaves;
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leaves.resize(block.vtx.size());
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for (size_t s = 0; s < block.vtx.size(); s++) {
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leaves[s] = block.vtx[s].GetHash();
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}
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return ComputeMerkleBranch(leaves, position);
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}
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// Older version of the merkle root computation code, for comparison.
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static uint256 BlockBuildMerkleTree(const CBlock& block, bool* fMutated, std::vector<uint256>& vMerkleTree)
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{
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vMerkleTree.clear();
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vMerkleTree.reserve(block.vtx.size() * 2 + 16); // Safe upper bound for the number of total nodes.
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for (std::vector<CTransaction>::const_iterator it(block.vtx.begin()); it != block.vtx.end(); ++it)
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vMerkleTree.push_back(it->GetHash());
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int j = 0;
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bool mutated = false;
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for (int nSize = block.vtx.size(); nSize > 1; nSize = (nSize + 1) / 2)
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{
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for (int i = 0; i < nSize; i += 2)
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{
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int i2 = std::min(i+1, nSize-1);
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if (i2 == i + 1 && i2 + 1 == nSize && vMerkleTree[j+i] == vMerkleTree[j+i2]) {
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// Two identical hashes at the end of the list at a particular level.
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mutated = true;
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}
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vMerkleTree.push_back(Hash(vMerkleTree[j+i].begin(), vMerkleTree[j+i].end(),
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vMerkleTree[j+i2].begin(), vMerkleTree[j+i2].end()));
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}
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j += nSize;
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}
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if (fMutated) {
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*fMutated = mutated;
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}
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return (vMerkleTree.empty() ? uint256() : vMerkleTree.back());
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}
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// Older version of the merkle branch computation code, for comparison.
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static std::vector<uint256> BlockGetMerkleBranch(const CBlock& block, const std::vector<uint256>& vMerkleTree, int nIndex)
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{
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std::vector<uint256> vMerkleBranch;
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int j = 0;
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for (int nSize = block.vtx.size(); nSize > 1; nSize = (nSize + 1) / 2)
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{
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int i = std::min(nIndex^1, nSize-1);
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vMerkleBranch.push_back(vMerkleTree[j+i]);
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nIndex >>= 1;
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j += nSize;
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}
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return vMerkleBranch;
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}
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static inline int ctz(uint32_t i) {
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if (i == 0) return 0;
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int j = 0;
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while (!(i & 1)) {
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j++;
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i >>= 1;
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}
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return j;
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}
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BOOST_AUTO_TEST_CASE(merkle_test)
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{
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for (int i = 0; i < 32; i++) {
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// Try 32 block sizes: all sizes from 0 to 16 inclusive, and then 15 random sizes.
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int ntx = (i <= 16) ? i : 17 + (InsecureRandRange(4000));
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// Try up to 3 mutations.
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for (int mutate = 0; mutate <= 3; mutate++) {
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int duplicate1 = mutate >= 1 ? 1 << ctz(ntx) : 0; // The last how many transactions to duplicate first.
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if (duplicate1 >= ntx) break; // Duplication of the entire tree results in a different root (it adds a level).
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int ntx1 = ntx + duplicate1; // The resulting number of transactions after the first duplication.
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int duplicate2 = mutate >= 2 ? 1 << ctz(ntx1) : 0; // Likewise for the second mutation.
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if (duplicate2 >= ntx1) break;
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int ntx2 = ntx1 + duplicate2;
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int duplicate3 = mutate >= 3 ? 1 << ctz(ntx2) : 0; // And for the the third mutation.
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if (duplicate3 >= ntx2) break;
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int ntx3 = ntx2 + duplicate3;
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// Build a block with ntx different transactions.
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CBlock block;
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block.vtx.resize(ntx);
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for (int j = 0; j < ntx; j++) {
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CMutableTransaction mtx;
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mtx.nLockTime = j;
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block.vtx[j] = mtx;
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}
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// Compute the root of the block before mutating it.
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bool unmutatedMutated = false;
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uint256 unmutatedRoot = BlockMerkleRoot(block, &unmutatedMutated);
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BOOST_CHECK(unmutatedMutated == false);
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// Optionally mutate by duplicating the last transactions, resulting in the same merkle root.
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block.vtx.resize(ntx3);
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for (int j = 0; j < duplicate1; j++) {
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block.vtx[ntx + j] = block.vtx[ntx + j - duplicate1];
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}
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for (int j = 0; j < duplicate2; j++) {
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block.vtx[ntx1 + j] = block.vtx[ntx1 + j - duplicate2];
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}
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for (int j = 0; j < duplicate3; j++) {
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block.vtx[ntx2 + j] = block.vtx[ntx2 + j - duplicate3];
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}
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// Compute the merkle root and merkle tree using the old mechanism.
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bool oldMutated = false;
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std::vector<uint256> merkleTree;
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uint256 oldRoot = BlockBuildMerkleTree(block, &oldMutated, merkleTree);
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// Compute the merkle root using the new mechanism.
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bool newMutated = false;
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uint256 newRoot = BlockMerkleRoot(block, &newMutated);
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BOOST_CHECK(oldRoot == newRoot);
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BOOST_CHECK(newRoot == unmutatedRoot);
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BOOST_CHECK((newRoot == uint256()) == (ntx == 0));
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BOOST_CHECK(oldMutated == newMutated);
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BOOST_CHECK(newMutated == !!mutate);
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// If no mutation was done (once for every ntx value), try up to 16 branches.
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if (mutate == 0) {
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for (int loop = 0; loop < std::min(ntx, 16); loop++) {
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// If ntx <= 16, try all branches. Otherwise, try 16 random ones.
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int mtx = loop;
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if (ntx > 16) {
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mtx = InsecureRandRange(ntx);
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}
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std::vector<uint256> newBranch = BlockMerkleBranch(block, mtx);
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std::vector<uint256> oldBranch = BlockGetMerkleBranch(block, merkleTree, mtx);
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BOOST_CHECK(oldBranch == newBranch);
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BOOST_CHECK(ComputeMerkleRootFromBranch(block.vtx[mtx].GetHash(), newBranch, mtx) == oldRoot);
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}
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}
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}
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}
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}
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BOOST_AUTO_TEST_SUITE_END()
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