gistfile1.txt

import java.net.*;
import java.io.*;
import java.util.HashMap;
import java.util.Iterator;

public class Vigenere {
	public static HashMap dict_hash;

	public static String encode(String toencode, String key) {
		char[] toencodearr = toencode.toCharArray();
		char[] keyarr = key.toCharArray();
		int keylen = keyarr.length;

		for(int i = 0; i < toencodearr.length; i++) {
			int charval, keyval, newval;
			if (Character.isUpperCase(toencodearr[i])) charval = (int)toencodearr[i] - 65;
			else charval = (int)toencodearr[i] - 97;
			if (Character.isUpperCase(keyarr[i % keylen])) keyval = (int)keyarr[i % keylen] - 65;
			else keyval = (int)keyarr[i % keylen] - 97;
			newval = (charval+keyval)%26;
			toencodearr[i] = (char)(newval+65);
		}
		String toreturn = new String(toencodearr);
		return toreturn;
	}

	public static String decode(String todecode, String key) {
		char[] todecodearr = todecode.toCharArray();
		char[] keyarr = key.toCharArray();
		int keylen = keyarr.length;

		for(int i = 0; i < todecodearr.length; i++) {
			int charval, keyval, newval;
			if (Character.isUpperCase(todecodearr[i])) charval = (int)todecodearr[i] - 65;
			else charval = (int)todecodearr[i] - 97;
			if (Character.isUpperCase(keyarr[i % keylen])) keyval = (int)keyarr[i % keylen] - 65;
			else keyval = (int)keyarr[i % keylen] - 97;
			newval = (charval-keyval)%26;
			if (newval < 0) newval += 26;
			todecodearr[i] = (char)(newval+65);
		}
		String toreturn = new String(todecodearr);
		return toreturn;		
	}

	public static void main(String[] args) {
		//System.out.println(encode("TODAYISMYBIRTHDAY", "REDDIT"));
		//System.out.println(decode("KSGDGBJQBEQKKLGDG", "REDDIT"));
		dict_hash = new HashMap(100000);

		//put contents of dictionary into a HashMap
		try {
			URL dict = new URL("http://docs.oracle.com/javase/tutorial/collections/interfaces/examples/dictionary.txt");
			BufferedReader input = new BufferedReader(new InputStreamReader(dict.openStream()));
			String line;
			while ((line = input.readLine()) != null) {
				dict_hash.put(line.hashCode(), line);
			}
		} catch (Exception e) {
			System.out.println("Some error has occurred");
		}

		String todecode = "ZEJFOKHTMSRMELCPODWHCGAW";
		String testkey, decoded;
		int counter=0;

		Iterator<String> iter = dict_hash.values().iterator();
		while (iter.hasNext()) {
			testkey = iter.next();
			if (testkey.length() <= 5) {
				decoded = decode(todecode, testkey);
				for (int i = 5; i < decoded.length(); i++) {
					String substr = decoded.substring(0, i).toLowerCase();
					if (dict_hash.get(substr.hashCode()) != null) System.out.println(testkey + " : " + decoded);
				}
			}
		}
	}
}