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-rw-r--r--src/main.cpp121
-rw-r--r--src/main.h90
-rw-r--r--src/test/pmt_tests.cpp98
3 files changed, 309 insertions, 0 deletions
diff --git a/src/main.cpp b/src/main.cpp
index 1c1de636a8..91fe6ba8fc 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -2262,6 +2262,127 @@ CMerkleBlock::CMerkleBlock(const CBlock& block, CBloomFilter& filter)
+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 beyong 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);
+ 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;
+}
+
+
+
+
+
+
+
+
bool CheckDiskSpace(uint64 nAdditionalBytes)
{
uint64 nFreeBytesAvailable = filesystem::space(GetDataDir()).available;
diff --git a/src/main.h b/src/main.h
index 77aac71d22..f6086e92c2 100644
--- a/src/main.h
+++ b/src/main.h
@@ -1110,11 +1110,101 @@ public:
+/** Data structure that represents a partial merkle tree.
+ *
+ * It respresents a subset of the txid's of a known block, in a way that
+ * allows recovery of the list of txid's and the merkle root, in an
+ * authenticated way.
+ *
+ * The encoding works as follows: we traverse the tree in depth-first order,
+ * storing a bit for each traversed node, signifying whether the node is the
+ * parent of at least one matched leaf txid (or a matched txid itself). In
+ * case we are at the leaf level, or this bit is 0, its merkle node hash is
+ * stored, and its children are not explorer further. Otherwise, no hash is
+ * stored, but we recurse into both (or the only) child branch. During
+ * decoding, the same depth-first traversal is performed, consuming bits and
+ * hashes as they written during encoding.
+ *
+ * The serialization is fixed and provides a hard guarantee about the
+ * encoded size:
+ *
+ * SIZE <= 10 + ceil(32.25*N)
+ *
+ * Where N represents the number of leaf nodes of the partial tree. N itself
+ * is bounded by:
+ *
+ * N <= total_transactions
+ * N <= 1 + matched_transactions*tree_height
+ *
+ * The serialization format:
+ * - uint32 total_transactions (4 bytes)
+ * - varint number of hashes (1-3 bytes)
+ * - uint256[] hashes in depth-first order (<= 32*N bytes)
+ * - varint number of bytes of flag bits (1-3 bytes)
+ * - byte[] flag bits, packed per 8 in a byte, least significant bit first (<= 2*N-1 bits)
+ * The size constraints follow from this.
+ */
+class CPartialMerkleTree
+{
+protected:
+ // the total number of transactions in the block
+ unsigned int nTransactions;
+
+ // node-is-parent-of-matched-txid bits
+ std::vector<bool> vBits;
+
+ // txids and internal hashes
+ std::vector<uint256> vHash;
+ // flag set when encountering invalid data
+ bool fBad;
+ // helper function to efficiently calculate the number of nodes at given height in the merkle tree
+ unsigned int CalcTreeWidth(int height) {
+ return (nTransactions+(1 << height)-1) >> height;
+ }
+
+ // calculate the hash of a node in the merkle tree (at leaf level: the txid's themself)
+ uint256 CalcHash(int height, unsigned int pos, const std::vector<uint256> &vTxid);
+
+ // recursive function that traverses tree nodes, storing the data as bits and hashes
+ void TraverseAndBuild(int height, unsigned int pos, const std::vector<uint256> &vTxid, const std::vector<bool> &vMatch);
+
+ // recursive function that traverses tree nodes, consuming the bits and hashes produced by TraverseAndBuild.
+ // it returns the hash of the respective node.
+ uint256 TraverseAndExtract(int height, unsigned int pos, unsigned int &nBitsUsed, unsigned int &nHashUsed, std::vector<uint256> &vMatch);
+
+public:
+ // serialization implementation
+ IMPLEMENT_SERIALIZE(
+ READWRITE(nTransactions);
+ READWRITE(vHash);
+ std::vector<unsigned char> vBytes;
+ if (fRead) {
+ READWRITE(vBytes);
+ CPartialMerkleTree &us = *(const_cast<CPartialMerkleTree*>(this));
+ us.vBits.resize(vBytes.size() * 8);
+ for (unsigned int p = 0; p < us.vBits.size(); p++)
+ us.vBits[p] = (vBytes[p / 8] & (1 << (p % 8))) != 0;
+ us.fBad = false;
+ } else {
+ vBytes.resize((vBits.size()+7)/8);
+ for (unsigned int p = 0; p < vBits.size(); p++)
+ vBytes[p / 8] |= vBits[p] << (p % 8);
+ READWRITE(vBytes);
+ }
+ )
+
+ // Construct a partial merkle tree from a list of transaction id's, and a mask that selects a subset of them
+ CPartialMerkleTree(const std::vector<uint256> &vTxid, const std::vector<bool> &vMatch);
+ CPartialMerkleTree();
+ // extract the matching txid's represented by this partial merkle tree.
+ // returns the merkle root, or 0 in case of failure
+ uint256 ExtractMatches(std::vector<uint256> &vMatch);
+};
/** Nodes collect new transactions into a block, hash them into a hash tree,
diff --git a/src/test/pmt_tests.cpp b/src/test/pmt_tests.cpp
new file mode 100644
index 0000000000..cf09421617
--- /dev/null
+++ b/src/test/pmt_tests.cpp
@@ -0,0 +1,98 @@
+#include <boost/test/unit_test.hpp>
+
+#include "uint256.h"
+#include "main.h"
+
+using namespace std;
+
+class CPartialMerkleTreeTester : public CPartialMerkleTree
+{
+public:
+ // flip one bit in one of the hashes - this should break the authentication
+ void Damage() {
+ unsigned int n = rand() % vHash.size();
+ int bit = rand() % 256;
+ uint256 &hash = vHash[n];
+ hash ^= ((uint256)1 << bit);
+ }
+};
+
+BOOST_AUTO_TEST_SUITE(pmt_tests)
+
+BOOST_AUTO_TEST_CASE(pmt_test1)
+{
+ static const unsigned int nTxCounts[] = {1, 4, 7, 17, 56, 100, 127, 256, 312, 513, 1000, 4095};
+
+ for (int n = 0; n < 12; n++) {
+ unsigned int nTx = nTxCounts[n];
+
+ // build a block with some dummy transactions
+ CBlock block;
+ for (unsigned int j=0; j<nTx; j++) {
+ CTransaction tx;
+ tx.nLockTime = rand(); // actual transaction data doesn't matter; just make the nLockTime's unique
+ block.vtx.push_back(tx);
+ }
+
+ // calculate actual merkle root and height
+ uint256 merkleRoot1 = block.BuildMerkleTree();
+ std::vector<uint256> vTxid(nTx, 0);
+ for (unsigned int j=0; j<nTx; j++)
+ vTxid[j] = block.vtx[j].GetHash();
+ int nHeight = 1, nTx_ = nTx;
+ while (nTx_ > 1) {
+ nTx_ = (nTx_+1)/2;
+ nHeight++;
+ }
+
+ // check with random subsets with inclusion chances 1, 1/2, 1/4, ..., 1/128
+ for (int att = 1; att < 15; att++) {
+ // build random subset of txid's
+ std::vector<bool> vMatch(nTx, false);
+ std::vector<uint256> vMatchTxid1;
+ for (unsigned int j=0; j<nTx; j++) {
+ bool fInclude = (rand() & ((1 << (att/2)) - 1)) == 0;
+ vMatch[j] = fInclude;
+ if (fInclude)
+ vMatchTxid1.push_back(vTxid[j]);
+ }
+
+ // build the partial merkle tree
+ CPartialMerkleTree pmt1(vTxid, vMatch);
+
+ // serialize
+ CDataStream ss(SER_NETWORK, PROTOCOL_VERSION);
+ ss << pmt1;
+
+ // verify CPartialMerkleTree's size guarantees
+ unsigned int n = std::min<unsigned int>(nTx, 1 + vMatchTxid1.size()*nHeight);
+ BOOST_CHECK(ss.size() <= 10 + (258*n+7)/8);
+
+ // deserialize into a tester copy
+ CPartialMerkleTreeTester pmt2;
+ ss >> pmt2;
+
+ // extract merkle root and matched txids from copy
+ std::vector<uint256> vMatchTxid2;
+ uint256 merkleRoot2 = pmt2.ExtractMatches(vMatchTxid2);
+
+ // check that it has the same merkle root as the original, and a valid one
+ BOOST_CHECK(merkleRoot1 == merkleRoot2);
+ BOOST_CHECK(merkleRoot2 != 0);
+
+ // check that it contains the matched transactions (in the same order!)
+ BOOST_CHECK(vMatchTxid1 == vMatchTxid2);
+
+ // check that random bit flips break the authentication
+ for (int j=0; j<4; j++) {
+ CPartialMerkleTreeTester pmt3(pmt2);
+ pmt3.Damage();
+ std::vector<uint256> vMatchTxid3;
+ uint256 merkleRoot3 = pmt3.ExtractMatches(vMatchTxid3);
+ BOOST_CHECK(merkleRoot3 != merkleRoot1);
+ }
+ }
+ }
+}
+
+BOOST_AUTO_TEST_SUITE_END()
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