Java Security

Hi,

my task is to decrypt a DESede encrypted privateKey with the help of a symmetric key derived from the string "secret" (a HMAC-SHA1 hash). This done for interoperability-testing of my XKMS-client-implementation.

The XKMS 2.0 Specification [1] says:

"[331]Keying material is derived from the shared string using a MAC
function.

[332]The default MAC algorithm used is HMAC-SHA1."

und further:

"[334]If the output of the MAC function provides more keying material than is required for a cryptographic operation (i.e. encryption, MAC), the lowest significant bits are used.

[335]If the output of the MAC function provides less keying material than is required additional keying material is obtained as follows: [...]"

The interoperability-service-provider [2] says:

"Shared Secret: secret"

I tried to achieve this as follows:

package test;

import java.security.Security;

import javax.crypto.Cipher;
import javax.crypto.Mac;
import javax.crypto.SecretKey;
import javax.crypto.SecretKeyFactory;
import javax.crypto.spec.DESedeKeySpec;
import javax.crypto.spec.SecretKeySpec;

import org.bouncycastle.jce.provider.BouncyCastleProvider;
import org.bouncycastle.util.encoders.Base64;

public class HashCalculator {

	private static String secret = "secret";
	private static String message =
"6VSIdlBUlS19IL4mI7Re75umJWtUBRHaqI3coi+G2l+peKphQw0fuOml6hDmTL9P" +
"ppozPO3pJdNdYb3soigl1cbeUoGMVAQYjxSDhb/7A/59ECQmfUSLCijGUB47RdMP" +
"gMHan4fTBKf/+PxJw4hBv5iK7gitoWAdYs3QJ4D3aY+gW+p253D4dDuHZXYjCoxH" +
"CPUtslGn/qAYgzExxBtp3Iw0v7Ow9lzaWt1275rIawIjYOdtVHMfDkLWSvilkzZu" +
"io5p+ci7h/z2Ngqjz1PeOxuI6SSjwDImdKQzGl1zBtAOC/BWQKiNC0sv4Gr3EAdO" +
"0+81c0Ayn8r/ZSiQ9SN0RSkE2Vo+8rtYaI6phPkmV7qR35nRoNjPBH6/YXrufQjx" +
"L9J5IZFvCWZJeZSLk8Y02OSqD+M30g14awHR30MuCkr3JF/Re3bxVBsU7sJZHetw" +
"NwilXbZiSiKCElLAFbag038LuhOxGg7zRQrKgwYTo2piEU3tGiDZDS/sqC9GYa4F" +
"yEu1K+vpqTv0iwX2RA8sD+2KF0UqCSrJkJImtfkFDgkXUf33CsPzl3G9ehpqzROe" +
"vQV+T2Pc8+fRK/7XtNrP7GBz6n4oAOvcLnz0EYdHkUJ0cPoesz+OEbJCB196kx5j" +
"gAlFsfBJtNheB0q55WypyE/vKnyr4lIacIXtrCRKzrecZHdVgf/k4VyvArz5RNIk" +
"LwQOvl0TQYSDf5cSx/8CRuYzt2vKzjfjzavoxlTgngHw203m5DE1Wji3U6CENdyp" +
"hvIS0TGM/i+Wa+EvvDEKEs9HtspJJ47XIXlcOHtoQCgLJdg94O+njC675NI8OQt0" +
"EDICvtPJk02hFTOAW8OWJIi72ams/ofxBFOKi6/u5XUFccjnVsdKNJCcCxmYw9a+" +
"WwyZ9ZjJPlOzpRDWxFm39joydySrsPqvdQI26gstxUgfyHE2QqsMczMK+soPyqRo" +
"gHS+ujIfcX9cW3tv8W6e4ZPNzuP04ccNUWVtYqWjAWf5VF6p9tqPzwpUWOdh0Z1y" +
"gevuy6XGA7M/6By+17Eenw6T53/XuFnzlfeNBF68Z/rBscquJQEbvCeZCKIZ/RKL" +
"zwIVcaSdvcEDJ5DudmjutcVyVOS/envgJr423oyv7VjrdYxF+O4TsxQKNPdEez4j" +
"jupRReM+X/ofI/+WIhr/YYpiXrlBn5qeIjwAmTnaOp9gSMkQ7rgoPgXCEyBU51+t" +
"Oa9qAFe9KYf9aFzNqDne8dk1A9JMO6FxBnSoyF1PaDtTzf424DLk9Ym4ZEsvUGT9" +
"fU1IC0gxb3UpV/jiGibW5Q==";

	public static void main(String[] args) {
		
		try {	
			Security.addProvider(new BouncyCastleProvider());

			String hmacSha1 = hmacSha1(secret, secret);
			SecretKey key = getSecretKey(hmacSha1);	
			String decryptedString = decrypt(key, message);
			
			System.out.println(decryptedString);
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
	
	private static String hmacSha1(String secret, String message) {
		
        byte[] mac = new byte[20];

        try {
            Mac sha = Mac.getInstance("HmacSHA1");
            sha.init(new SecretKeySpec(secret.getBytes("UTF-8"), "HmacSHA1"));
            mac = sha.doFinal(message.getBytes("UTF-8"));
        } catch (Exception e) {
            e.printStackTrace();
        }

        return hex(mac);
    }
    
    private static String hex(byte[] data) {
    	
        StringBuilder sb = new StringBuilder();
        
        for (byte b : data) {
            sb.append(Character.forDigit((b & 240) >> 4, 16));
            sb.append(Character.forDigit((b & 15), 16));
        }
        
        return sb.toString();
    }
    
    private static SecretKey getSecretKey(String hmacSha1) 
	throws Exception {
		
		DESedeKeySpec keyspec = new DESedeKeySpec(hmacSha1.getBytes("UTF-8"));
		SecretKeyFactory keyfactory = SecretKeyFactory.getInstance("DESede");
		SecretKey key = keyfactory.generateSecret(keyspec);
		
		return key;
	}

    private static String decrypt(SecretKey key, String base64) 
	throws Exception {
		
		byte[] encryptedString = Base64.decode(base64);

		Cipher cipher = Cipher.getInstance("DESede");
		cipher.init(Cipher.DECRYPT_MODE, key);

		byte[] decryptedString = cipher.doFinal(encryptedString);
		
		return new String(decryptedString);
	}
}

but I only the the following exception back after executing the program:

"javax.crypto.BadPaddingException: Given final block not properly padded"

How can this be fixed? The main problem is, that I do not know how to derive the key material to create a valid SecretKey.

Would anyone please be so kind and help me with that?

Thank you,
Michael.

--
[1] http://www.w3.org/TR/xkms2/#XKMS_2_0_Section_8_1
[2] http://www.soapclient.com/xkmstest.html