BreakDigest.java

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.File;
import java.io.FileWriter;
import java.security.*;
import java.io.PrintWriter;

public class BreakDigest{


	public static void main(String [] args) throws Exception{
		
		
		if(args.length>0){
			
			MessageDigest md = MessageDigest.getInstance("MD5");
			BufferedReader br;
		
			File digestFile = new File("digest.txt");
			String currentLine="";
		
			if(!digestFile.exists()){ //if digestfile doesn't exist, create it from dict.txt
			
				br = new BufferedReader(new FileReader("dict.txt"));
			
				PrintWriter digestWriter =new PrintWriter(new FileWriter("digest.txt"));
			
		
				byte [] lineArray;
			
				byte [] lineDigest = new byte[32];
				String digestedLine="";
			
				while((currentLine=br.readLine())!=null){
			
					lineArray=currentLine.getBytes();
				
					lineDigest=md.digest(lineArray);
					StringBuffer lineBuffer = new StringBuffer();
					String hexchar;
					for (int i=0; i < lineDigest.length; i++) { //convert digest to hex
					
						hexchar = Integer.toHexString((int)(lineDigest[i] & 0xFF));
						if (hexchar.length() == 1) hexchar = "0" + hexchar;
						lineBuffer.append(hexchar);
				
  					}
				
				
					digestedLine=lineBuffer.toString();
				
					digestWriter.println(currentLine+" "+digestedLine); //output digest paired with plaintext to digest.txt
				
				}
			
				digestWriter.close();
				currentLine="";
			
			}
	
			br = new BufferedReader(new FileReader(digestFile));
			String [] lineSplit;
		
			boolean matchFound=false;
			while((currentLine=br.readLine())!=null){
				lineSplit =currentLine.split(" ");
			
			
				if(md.isEqual(args[0].getBytes(),lineSplit[1].getBytes())){ //check inputted digest against digest.text
						
					System.out.println(lineSplit[0]);
					matchFound=true;
					break;
				} 
				
				
			}
			if(!matchFound){
			
				System.out.println("no matches found");	
			
			}
			
		}
		
	}
}