src/test/merkle_tests.cpp

   1 // Copyright (c) 2015-2016 The Bitcoin Core developers
   2 // Distributed under the MIT software license, see the accompanying
   3 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
   4
   5 #include "consensus/merkle.h"
   6 #include "test/test_bitcoin.h"
   7
   8 #include <boost/test/unit_test.hpp>
   9
  10 BOOST_FIXTURE_TEST_SUITE(merkle_tests, TestingSetup)
  11
  12 // Older version of the merkle root computation code, for comparison.
  13 static uint256 BlockBuildMerkleTree(const CBlock& block, bool* fMutated, std::vector<uint256>& vMerkleTree)
  14 {
  15     vMerkleTree.clear();
  16     vMerkleTree.reserve(block.vtx.size() * 2 + 16); // Safe upper bound for the number of total nodes.
  17     for (std::vector<CTransactionRef>::const_iterator it(block.vtx.begin()); it != block.vtx.end(); ++it)
  18         vMerkleTree.push_back((*it)->GetHash());
  19     int j = 0;
  20     bool mutated = false;
  21     for (int nSize = block.vtx.size(); nSize > 1; nSize = (nSize + 1) / 2)
  22     {
  23         for (int i = 0; i < nSize; i += 2)
  24         {
  25             int i2 = std::min(i+1, nSize-1);
  26             if (i2 == i + 1 && i2 + 1 == nSize && vMerkleTree[j+i] == vMerkleTree[j+i2]) {
  27                 // Two identical hashes at the end of the list at a particular level.
  28                 mutated = true;
  29             }
  30             vMerkleTree.push_back(Hash(vMerkleTree[j+i].begin(), vMerkleTree[j+i].end(),
  31                                        vMerkleTree[j+i2].begin(), vMerkleTree[j+i2].end()));
  32         }
  33         j += nSize;
  34     }
  35     if (fMutated) {
  36         *fMutated = mutated;
  37     }
  38     return (vMerkleTree.empty() ? uint256() : vMerkleTree.back());
  39 }
  40
  41 // Older version of the merkle branch computation code, for comparison.
  42 static std::vector<uint256> BlockGetMerkleBranch(const CBlock& block, const std::vector<uint256>& vMerkleTree, int nIndex)
  43 {
  44     std::vector<uint256> vMerkleBranch;
  45     int j = 0;
  46     for (int nSize = block.vtx.size(); nSize > 1; nSize = (nSize + 1) / 2)
  47     {
  48         int i = std::min(nIndex^1, nSize-1);
  49         vMerkleBranch.push_back(vMerkleTree[j+i]);
  50         nIndex >>= 1;
  51         j += nSize;
  52     }
  53     return vMerkleBranch;
  54 }
  55
  56 static inline int ctz(uint32_t i) {
  57     if (i == 0) return 0;
  58     int j = 0;
  59     while (!(i & 1)) {
  60         j++;
  61         i >>= 1;
  62     }
  63     return j;
  64 }
  65
  66 BOOST_AUTO_TEST_CASE(merkle_test)
  67 {
  68     for (int i = 0; i < 32; i++) {
  69         // Try 32 block sizes: all sizes from 0 to 16 inclusive, and then 15 random sizes.
  70         int ntx = (i <= 16) ? i : 17 + (InsecureRandRange(4000));
  71         // Try up to 3 mutations.
  72         for (int mutate = 0; mutate <= 3; mutate++) {
  73             int duplicate1 = mutate >= 1 ? 1 << ctz(ntx) : 0; // The last how many transactions to duplicate first.
  74             if (duplicate1 >= ntx) break; // Duplication of the entire tree results in a different root (it adds a level).
  75             int ntx1 = ntx + duplicate1; // The resulting number of transactions after the first duplication.
  76             int duplicate2 = mutate >= 2 ? 1 << ctz(ntx1) : 0; // Likewise for the second mutation.
  77             if (duplicate2 >= ntx1) break;
  78             int ntx2 = ntx1 + duplicate2;
  79             int duplicate3 = mutate >= 3 ? 1 << ctz(ntx2) : 0; // And for the third mutation.
  80             if (duplicate3 >= ntx2) break;
  81             int ntx3 = ntx2 + duplicate3;
  82             // Build a block with ntx different transactions.
  83             CBlock block;
  84             block.vtx.resize(ntx);
  85             for (int j = 0; j < ntx; j++) {
  86                 CMutableTransaction mtx;
  87                 mtx.nLockTime = j;
  88                 block.vtx[j] = MakeTransactionRef(std::move(mtx));
  89             }
  90             // Compute the root of the block before mutating it.
  91             bool unmutatedMutated = false;
  92             uint256 unmutatedRoot = BlockMerkleRoot(block, &unmutatedMutated);
  93             BOOST_CHECK(unmutatedMutated == false);
  94             // Optionally mutate by duplicating the last transactions, resulting in the same merkle root.
  95             block.vtx.resize(ntx3);
  96             for (int j = 0; j < duplicate1; j++) {
  97                 block.vtx[ntx + j] = block.vtx[ntx + j - duplicate1];
  98             }
  99             for (int j = 0; j < duplicate2; j++) {
 100                 block.vtx[ntx1 + j] = block.vtx[ntx1 + j - duplicate2];
 101             }
 102             for (int j = 0; j < duplicate3; j++) {
 103                 block.vtx[ntx2 + j] = block.vtx[ntx2 + j - duplicate3];
 104             }
 105             // Compute the merkle root and merkle tree using the old mechanism.
 106             bool oldMutated = false;
 107             std::vector<uint256> merkleTree;
 108             uint256 oldRoot = BlockBuildMerkleTree(block, &oldMutated, merkleTree);
 109             // Compute the merkle root using the new mechanism.
 110             bool newMutated = false;
 111             uint256 newRoot = BlockMerkleRoot(block, &newMutated);
 112             BOOST_CHECK(oldRoot == newRoot);
 113             BOOST_CHECK(newRoot == unmutatedRoot);
 114             BOOST_CHECK((newRoot == uint256()) == (ntx == 0));
 115             BOOST_CHECK(oldMutated == newMutated);
 116             BOOST_CHECK(newMutated == !!mutate);
 117             // If no mutation was done (once for every ntx value), try up to 16 branches.
 118             if (mutate == 0) {
 119                 for (int loop = 0; loop < std::min(ntx, 16); loop++) {
 120                     // If ntx <= 16, try all branches. Otherwise, try 16 random ones.
 121                     int mtx = loop;
 122                     if (ntx > 16) {
 123                         mtx = InsecureRandRange(ntx);
 124                     }
 125                     std::vector<uint256> newBranch = BlockMerkleBranch(block, mtx);
 126                     std::vector<uint256> oldBranch = BlockGetMerkleBranch(block, merkleTree, mtx);
 127                     BOOST_CHECK(oldBranch == newBranch);
 128                     BOOST_CHECK(ComputeMerkleRootFromBranch(block.vtx[mtx]->GetHash(), newBranch, mtx) == oldRoot);
 129                 }
 130             }
 131         }
 132     }
 133 }
 134
 135 BOOST_AUTO_TEST_SUITE_END()