130 lines
4.9 KiB
C++
130 lines
4.9 KiB
C++
// Copyright (c) 2009-2010 Satoshi Nakamoto
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// Copyright (c) 2009-2014 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 "primitives/block.h"
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#include "hash.h"
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#include "tinyformat.h"
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#include "utilstrencodings.h"
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uint256 CBlockHeader::GetHash() const
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{
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return Hash(BEGIN(nVersion), END(nNonce));
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}
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uint256 CBlock::BuildMerkleTree(bool* fMutated) const
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{
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/* WARNING! If you're reading this because you're learning about crypto
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and/or designing a new system that will use merkle trees, keep in mind
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that the following merkle tree algorithm has a serious flaw related to
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duplicate txids, resulting in a vulnerability (CVE-2012-2459).
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The reason is that if the number of hashes in the list at a given time
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is odd, the last one is duplicated before computing the next level (which
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is unusual in Merkle trees). This results in certain sequences of
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transactions leading to the same merkle root. For example, these two
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trees:
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A A
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/ \ / \
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B C B C
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/ \ | / \ / \
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D E F D E F F
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/ \ / \ / \ / \ / \ / \ / \
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1 2 3 4 5 6 1 2 3 4 5 6 5 6
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for transaction lists [1,2,3,4,5,6] and [1,2,3,4,5,6,5,6] (where 5 and
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6 are repeated) result in the same root hash A (because the hash of both
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of (F) and (F,F) is C).
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The vulnerability results from being able to send a block with such a
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transaction list, with the same merkle root, and the same block hash as
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the original without duplication, resulting in failed validation. If the
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receiving node proceeds to mark that block as permanently invalid
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however, it will fail to accept further unmodified (and thus potentially
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valid) versions of the same block. We defend against this by detecting
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the case where we would hash two identical hashes at the end of the list
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together, and treating that identically to the block having an invalid
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merkle root. Assuming no double-SHA256 collisions, this will detect all
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known ways of changing the transactions without affecting the merkle
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root.
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*/
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vMerkleTree.clear();
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vMerkleTree.reserve(vtx.size() * 2 + 16); // Safe upper bound for the number of total nodes.
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for (std::vector<CTransaction>::const_iterator it(vtx.begin()); it != 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 = 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(BEGIN(vMerkleTree[j+i]), END(vMerkleTree[j+i]),
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BEGIN(vMerkleTree[j+i2]), END(vMerkleTree[j+i2])));
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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() ? 0 : vMerkleTree.back());
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}
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std::vector<uint256> CBlock::GetMerkleBranch(int nIndex) const
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{
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if (vMerkleTree.empty())
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BuildMerkleTree();
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std::vector<uint256> vMerkleBranch;
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int j = 0;
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for (int nSize = 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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uint256 CBlock::CheckMerkleBranch(uint256 hash, const std::vector<uint256>& vMerkleBranch, int nIndex)
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{
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if (nIndex == -1)
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return 0;
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for (std::vector<uint256>::const_iterator it(vMerkleBranch.begin()); it != vMerkleBranch.end(); ++it)
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{
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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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nIndex >>= 1;
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}
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return hash;
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}
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std::string CBlock::ToString() const
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{
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std::stringstream s;
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s << strprintf("CBlock(hash=%s, ver=%d, hashPrevBlock=%s, hashMerkleRoot=%s, nTime=%u, nBits=%08x, nNonce=%u, vtx=%u)\n",
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GetHash().ToString(),
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nVersion,
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hashPrevBlock.ToString(),
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hashMerkleRoot.ToString(),
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nTime, nBits, nNonce,
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vtx.size());
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for (unsigned int i = 0; i < vtx.size(); i++)
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{
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s << " " << vtx[i].ToString() << "\n";
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}
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s << " vMerkleTree: ";
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for (unsigned int i = 0; i < vMerkleTree.size(); i++)
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s << " " << vMerkleTree[i].ToString();
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s << "\n";
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return s.str();
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}
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