Question

Write down a Java program that calculates the Merkle root for the following dataset:

7246

9716

2017

6329

2831

1171

5690

7739

9463

8363

Answer 1

Java Program to Calculate Merkel Root from a dataset:

Merkel Root : Merkel Root is the final created hash from the input dataset, it is a Blockchain technology and is used to summarize all the transactions in a block. Currently used with Bitcoin it  produces overall digital fingerprint of the entire set of transactions, and provide a very efficient process for verifying if a transaction is included in a block or not.

/*Program starts here*/

import java.security.MessageDigest;
import java.util.ArrayList;
import java.util.List;

public class MerkleTrees {

// Dataset list for capturing the data inputs
List<String> txnList;
// Merkle Root Variable ( String Type )
String root;
  
//Constructor
public MerkleTrees(List<String> txnList) {
this.txnList = txnList;
root = "";
}

//Merkle_tree execution with void return type used to set root.
public void merkle_tree() {
  
List<String> tempTxnList = new ArrayList<String>();
  

//Loop for capturing the dataset
for (int i = 0; i < this.txnList.size(); i++) {
tempTxnList.add(this.txnList.get(i));
}
  
List<String> newTxnList = getNewTxnList(tempTxnList);
while (newTxnList.size() != 1) {
newTxnList = getNewTxnList(newTxnList);
}
  
this.root = newTxnList.get(0);
}
  
/Return Node Hash List, Private access specifier.
private List<String> getNewTxnList(List<String> tempTxnList) {
  
List<String> newTxnList = new ArrayList<String>();
int index = 0;
while (index < tempTxnList.size()) {
// left
String left = tempTxnList.get(index);
index++;

// right
String right = "";
if (index != tempTxnList.size()) {
right = tempTxnList.get(index);
}

// sha2 hex value
String sha2HexValue = getSHA2HexValue(left + right);
newTxnList.add(sha2HexValue);
index++;
  
}
  
return newTxnList;
}
  
//Returning hex string
public String getSHA2HexValue(String str) {
byte[] cipher_byte;

//Exception handeling with Try block
try{
MessageDigest md = MessageDigest.getInstance("SHA-256");
md.update(str.getBytes());
cipher_byte = md.digest();
StringBuilder sb = new StringBuilder(2 * cipher_byte.length);
for(byte b: cipher_byte) {
sb.append(String.format("%02x", b&0xff) );
}
return sb.toString();
} catch (Exception e) {
e.printStackTrace();
}
  
return "";
}
  
//Get Root, String return type
public String getRoot() {
return this.root;
}
  
}

/*Program ends here*/

Answer 2

Please find the three classes and output file.

Answer 3