org.bitcoinj.utils.MerkleRoot Maven / Gradle / Ivy
/*
* Copyright 2024 Dash Core Group
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.bitcoinj.utils;
import org.bitcoinj.core.Sha256Hash;
import org.bitcoinj.core.Utils;
import java.util.ArrayList;
import java.util.List;
import static org.bitcoinj.core.Sha256Hash.hashTwice;
public final class MerkleRoot {
private MerkleRoot() {}
public static Sha256Hash calculateMerkleRoot(List hashes) {
List tree = buildMerkleTree(hashes);
return Sha256Hash.wrap(tree.get(tree.size() - 1));
}
private static List buildMerkleTree(List hashes) {
// The Merkle root is based on a tree of hashes calculated from the masternode list proRegHash:
//
// root
// / \
// A B
// / \ / \
// t1 t2 t3 t4
//
// The tree is represented as a list: t1,t2,t3,t4,A,B,root where each
// entry is a hash.
//
// The hashing algorithm is double SHA-256. The leaves are a hash of the serialized contents of the transaction.
// The interior nodes are hashes of the concenation of the two child hashes.
//
// This structure allows the creation of proof that a transaction was included into a block without having to
// provide the full block contents. Instead, you can provide only a Merkle branch. For example to prove tx2 was
// in a block you can just provide tx2, the hash(tx1) and B. Now the other party has everything they need to
// derive the root, which can be checked against the block header. These proofs aren't used right now but
// will be helpful later when we want to download partial block contents.
//
// Note that if the number of transactions is not even the last tx is repeated to make it so (see
// tx3 above). A tree with 5 transactions would look like this:
//
// root
// / \
// 1 5
// / \ / \
// 2 3 4 4
// / \ / \ / \
// t1 t2 t3 t4 t5 t5
ArrayList tree = new ArrayList();
// Start by adding all the hashes of the transactions as leaves of the tree.
for (Sha256Hash hash : hashes) {
tree.add(hash.getBytes());
}
int levelOffset = 0; // Offset in the list where the currently processed level starts.
// Step through each level, stopping when we reach the root (levelSize == 1).
for (int levelSize = hashes.size(); levelSize > 1; levelSize = (levelSize + 1) / 2) {
// For each pair of nodes on that level:
for (int left = 0; left < levelSize; left += 2) {
// The right hand node can be the same as the left hand, in the case where we don't have enough
// transactions.
int right = Math.min(left + 1, levelSize - 1);
byte[] leftBytes = Utils.reverseBytes(tree.get(levelOffset + left));
byte[] rightBytes = Utils.reverseBytes(tree.get(levelOffset + right));
tree.add(Utils.reverseBytes(hashTwice(leftBytes, 0, 32, rightBytes, 0, 32)));
}
// Move to the next level.
levelOffset += levelSize;
}
return tree;
}
}