This switches the Merkle tree logic for blocks to one that runs in constant (small) space. The old code is moved to tests, and a new test is added that for various combinations of block sizes, transaction positions to compute a branch for, and mutations: * Verifies that the old code and new code agree for the Merkle root. * Verifies that the old code and new code agree for the Merkle branch. * Verifies that the computed Merkle branch is valid. * Verifies that mutations don't change the Merkle root. * Verifies that mutations are correctly detected.pull/262/head
Pieter Wuille
9 years ago
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ee60e5625b
commit
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// 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 "random.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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// 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 + (insecure_rand() % 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. Otherise, try 16 random ones.
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int mtx = loop;
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if (ntx > 16) {
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mtx = insecure_rand() % 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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