Add CPartialMerkleTree

This adds a compact representation for a subset of a merkle tree's
nodes.

1 files changed, 98 insertions, 0 deletions

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()