Java crypto

Posted on 2011-02-13
Last Modified: 2012-05-11
String hashPassword = md5(arg4);

byte[] hPassword = AES.getAESKey(hashPassword, "888");
response = AES.encrypt(hPassword, "challenge");


String driverHash = hashPassword;

byte[] driver_hash = AES.getAESKey(driverHash, "888");
String checkResponse = AES.decrypt(driver_hash, "challenge");

I compiled the codes. no error. Tried running the codes, I got a java.lang.NumberFormatException: For input string: "ch"

When I changed "challenge" to a single digit "1", it can run fine. Im stuck. What can be the problem??
Question by:moombaz
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LVL 47

Expert Comment

ID: 34883763
Sorry, I was trying to find this method getAESKey in Java Crypto API, and
somehow, I could not. What is the type of this AES in your code, or
is it a static method. But could not find class AES in Java Crypto either.

Most obvious general point is that it expects String which should be possible to be evaluated
as integer (so "1" will work and "challenge" would not, did you try some other number?),
 but this is certainly not too helpful.

Perhaps someone with experience in Crypto would advise.

Still if you elaborate a little bit on the context, maybe it will help.

Author Comment

ID: 34884896
hi for_yan,

im using all of this

import java.util.*;
import java.text.*;
import cryptosystem.*;
LVL 47

Expert Comment

ID: 34884914
So is AES a class within these packages or it is an instance
of some class? If the latter, then what is the class name?
I was looking for a method getAESKey in Java crypto
but it for some reason escapes me.
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LVL 47

Expert Comment

ID: 34884944

Do you have a link to the API documentation for these classes?
Those which I see for Java crypto don't seem to contain this stuff.
Is getAESKey method something which is part of your program, not some method from API?

Author Comment

ID: 34885037
No I just call it directly. Im not calling from another class or method

Author Comment

ID: 34885043
ouh.. my bad.. it is from this class.

package cryptosystem;

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


public class AES {
	public static String asHex (byte buf[]){
		StringBuffer strbuf = new StringBuffer(buf.length*2);
		int i;
		for(i=0; i<buf.length;i++){
			if(((int) buf[i] & 0xff) < 0x10)
			strbuf.append(Long.toString((int) buf[i] & 0xff, 16));
		return strbuf.toString();
	public static byte[] asByte (String hex){
		byte[] bts = new byte[hex.length()/2];
		for(int i=0;i<bts.length;i++){
			bts[i] = (byte) Integer.parseInt(hex.substring(2*i, 2*i+2), 16);
		return bts;
	/* returns a 128 bit key */
	public static byte[] getAESKey(String password, String salt) 
													throws Exception{
		int IC = 2;
		byte[] keyBytes = null;
		MessageDigest md = MessageDigest.getInstance("MD5");
		for(int i=1; i<IC; i++){
		keyBytes = md.digest();
		return keyBytes;
	public static byte[] generateKey(){
		byte[] raw = null;
		try {
			KeyGenerator kgen = KeyGenerator.getInstance("AES");
			SecretKey skey = kgen.generateKey();
			raw = skey.getEncoded();
		}catch (NoSuchAlgorithmException e){
		return raw;
	public static String encrypt(byte[] key, String plainText) 
													throws Exception{
		byte[] encrypted = null;
		SecretKeySpec sKeySpec = new SecretKeySpec(key, "AES");
		Cipher cipher = Cipher.getInstance("AES");
		cipher.init(Cipher.ENCRYPT_MODE, sKeySpec);
		encrypted = cipher.doFinal(plainText.getBytes());
		return asHex(encrypted);
	public static String decrypt(byte[] key, String cipherText) 
													throws Exception{
		byte[] decrypted = null;
		SecretKeySpec sKeySpec = new SecretKeySpec(key, "AES");
		Cipher cipher = Cipher.getInstance("AES");
		cipher.init(Cipher.DECRYPT_MODE, sKeySpec);
		decrypted = cipher.doFinal(asByte(cipherText));
		return new String(decrypted);
	public static void main(String[] args) throws Exception {
		String message="This is just an example";
		String password = "apple1";
		String salt = "47BCE5C74F589F4867DBD57E9CA9F808";
		// Create a key
		byte[] key = getAESKey(password, salt);
		String hex = asHex(key);
		System.out.println("hex: "+hex+" Len:"+hex.getBytes().length);
		String hash = "48c27a623063a286358e0bf65bd5afbd";
		byte[] hashBytes = asByte(hash);
		boolean expected = java.util.Arrays.equals(hashBytes, key);
		System.out.println("Test " + (expected ? "SUCCEEDED!" : "FAILED!"));
		String encrypted = encrypt(key, message);
		System.out.println("encrypted: "+encrypted);
		String original = decrypt(hashBytes, encrypted);
		System.out.println("original: "+original);

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LVL 47

Accepted Solution

for_yan earned 500 total points
ID: 34885185
Is "challenge" - is something that you yourself specify?
As you understand I'm no specialist in this stuff, but looking at this code
it seems to me that it expects in this place the string which has only Hex number,
which means this string is a key which should be made up of digits and letters "a" through "f",
that's why "challenge"  which contains "h" and "l" and "g" causes problems.
If this is something you select yourself - try to select the key following this rule,
say 3a4b2345e should be fine, but 1t34s - is not good as "s" and "t" has no meaning in Hex number.

Author Comment

ID: 34885663
I've tried and it doesnt work. "challenge" i replaced to "3a4b2345e". Error message that I got is javax.crypto.IllegalBlockSizeException: Input length must be multiple of 16.

Still doesnt work. anw, i have been encrypting and decrypting using the same key. all of them works except for this one.

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