Crypt.java

import java.security.GeneralSecurityException;

import javax.crypto.Cipher;
import javax.crypto.spec.SecretKeySpec;

import util.B64;


public class Crypt {
	
	public static void main(String[] args) throws Exception {
		
		// Receive Key
		String KEY = "57238004e784498bbc2f8bf984565090";
		
		// Message
		String MSG = "HELLO WORLD";
		
		// Example
		String encrypt = encrypt(MSG, KEY);
		String decrypt = decrypt(B64.dec(encrypt), B64.enc(KEY));
	}
	
	public static String encrypt(String msg, String keyHexString) throws GeneralSecurityException {
		Cipher cipher = Cipher.getInstance("AES/ECB/PKCS5Padding");
	    SecretKeySpec sks = new SecretKeySpec(hexStringToByteArray(keyHexString), "AES");
	    cipher.init(Cipher.ENCRYPT_MODE, sks, cipher.getParameters());
	    byte[] encrypted = cipher.doFinal(msg.getBytes());
	    return new String(B64.enc(byteArrayToHexString(encrypted)));
	}
	
	public static String decrypt(String msg64String, String keyHex64String) throws Exception {
		Cipher cipher = Cipher.getInstance("AES/ECB/PKCS5Padding");
		SecretKeySpec sks =  new SecretKeySpec(hexStringToByteArray(B64.dec(keyHex64String)), "AES");
	    cipher.init(Cipher.DECRYPT_MODE, sks, cipher.getParameters());
	    byte[] encrypted = cipher.doFinal(hexStringToByteArray(msg64String));
        return new String(encrypted);
	}

	public static byte[] hexStringToByteArray(String s) {
	    byte[] b = new byte[s.length() / 2];
	    for (int i = 0; i < b.length; i++) {
	        int index = i * 2;
	        int v = Integer.parseInt(s.substring(index, index + 2), 16);
	        b[i] = (byte) v;
	    }
	    return b;
	}

	public static String byteArrayToHexString(byte[] b) {
	    StringBuilder sb = new StringBuilder(b.length * 2);
	    for (int i = 0; i < b.length; i++) {
	        int v = b[i] & 0xff;
	        if (v < 16) {
	            sb.append('0');
	        }
	        sb.append(Integer.toHexString(v));
	    }
	    return sb.toString().toUpperCase();
	}

}