HashBreaker.java

public class HashBreaker { 
  public static void main(String[] args) throws NoSuchAlgorithmException { 
    var scanner = new Scanner(System.in); 
    System.out.println("Nonce Finder"); 
    System.out.print("Message : "); 
    String message = scanner.nextLine(); 
    System.out.print("Difficulty : "); 
    int d = scanner.nextInt(); 
    System.out.println("\nCalculating..."); 
    long startTime = System.currentTimeMillis(); 
    long nonce = bruteforce(d, message); 
    long endTime = System.currentTimeMillis(); 
    System.out.println("\nValid Nonce : " + nonce); 
    System.out.println("Hash : " + sha256(message + String.valueOf(nonce))); 
    System.out.println("Time taken : " + (endTime - startTime)/1000 + " seconds"); 
    scanner.close(); 
  } 
  
  public static String sha256(String text) throws NoSuchAlgorithmException { 
    MessageDigest digest = MessageDigest.getInstance("SHA-256"); 
    digest.update(text.getBytes(StandardCharsets.UTF_8)); 
    byte[] hash = digest.digest(); 
    StringBuffer sb = new StringBuffer(); 
    for (int i = 0; i < hash.length; i++) sb.append(Integer.toString((hash[i] & 0xff) + 0x100, 16).substring(1)); 
    return sb.toString().toUpperCase(); 
  } 
  
  public static long bruteforce(int d, String s) throws NoSuchAlgorithmException { 
    long nonce = 0; 
    String pre = ""; 
    for (; pre.length()<d; pre += "0"); 
    while (!sha256(s + String.valueOf(nonce)).startsWith(pre)){ 
      nonce++; 
    } 
    return nonce; 
  }
}