Java Decryption problem

[sirlink99]

I am attempting to encrypt and string and then decrypt it. I have the encryption part working, but when I try to decrypt it gives me an InvalidKeyException and says that it is missing parameters.

Here is the code

import javax.crypto.*;

import java.security.*;


public class Cryption {

    private Cipher c;
    private Key k;
    public Cryption(){
        try {
            c = Cipher.getInstance("DES/CBC/PKCS5Padding");
            KeyGenerator kg = KeyGenerator.getInstance("DES");
            k = kg.generateKey();
        } catch (NoSuchAlgorithmException | NoSuchPaddingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    public String encrypt(String dec){
        try {
            c.init(Cipher.ENCRYPT_MODE, k);
            String enc = new String(c.doFinal(dec.getBytes()));
            return enc;
        } catch (InvalidKeyException | IllegalBlockSizeException | BadPaddingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }   
        return null;
    }

    public String decrypt(String enc){
        try {
            c.init(Cipher.DECRYPT_MODE, k);
            String dec = new String(c.doFinal(enc.getBytes()));
            return dec;
        } catch (InvalidKeyException | IllegalBlockSizeException | BadPaddingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return null;
    }
}

and here is the output that I get when I run the program passing in the string Hello World

Hello World
oØÁÖG  _|bÁW3° 
java.security.InvalidKeyException: Parameters missing
    at com.sun.crypto.provider.CipherCore.init(CipherCore.java:388)
    at com.sun.crypto.provider.DESCipher.engineInit(DESCipher.java:186)
    at javax.crypto.Cipher.init(Cipher.java:1210)
    at javax.crypto.Cipher.init(Cipher.java:1153)
    at Cryption.decrypt(Cryption.java:35)
    at Main.main(Main.java:12)
null

The main method mentioned is just a test class

[stultuske]

why do you return null from those methods? I think it would be better to throw an Exception from the catch block, or have your method throw the exception instead of handling with it.

the main method is just a test class ... yeah well, since we don't know what code is in that 'test class', we can't really say much about it, can we?

[sirlink99]

Here is the main class. Like I said it is a very simple test class

public class Main {

    public static void main(String[] args) {
        Cryption c = new Cryption();

        String text = "Hello World";
        System.out.println(text);
        String encText = c.encrypt(text);
        System.out.println(encText);
        String decText = c.decrypt(encText);
        System.out.println(decText);
    }

}

After throwing the exceptions this is what my code looks like

import javax.crypto.*;

import java.security.*;


public class Cryption {

    private Cipher c;
    private Key k;
    public Cryption(){
        try {
            c = Cipher.getInstance("DES/CBC/PKCS5Padding");
            KeyGenerator kg = KeyGenerator.getInstance("DES");
            k = kg.generateKey();
        } catch (NoSuchAlgorithmException | NoSuchPaddingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    public String encrypt(String dec) throws InvalidKeyException, IllegalBlockSizeException, BadPaddingException{
            c.init(Cipher.ENCRYPT_MODE, k);
            String enc = new String(c.doFinal(dec.getBytes()));
            return enc;

    }

    public String decrypt(String enc) throws InvalidKeyException, IllegalBlockSizeException, BadPaddingException{
            c.init(Cipher.DECRYPT_MODE, k);
            String dec = new String(c.doFinal(enc.getBytes()));
            return dec;
    }
}

Thanks for the help.

[stultuske]

don't forget to catch those exceptions in your main method.

puzzled a bit with your code, and added an IvParameterSpec with which I got it to work:

here I hardcoded the value, of course it's better to have one generated, so that each encryption has it's own key.

public String encrypt(String dec) throws InvalidKeyException, IllegalBlockSizeException, BadPaddingException, InvalidAlgorithmParameterException {
byte[] iv = { 0, 0, 0, 0, 0, 0, 0, 0 };
IvParameterSpec ivspec = new IvParameterSpec(iv);
c.init(Cipher.ENCRYPT_MODE, k, ivspec);
String enc = new String(c.doFinal(dec.getBytes()));
return enc;
}

public String decrypt(String enc) throws InvalidKeyException, IllegalBlockSizeException, BadPaddingException, InvalidAlgorithmParameterException {
byte[] iv = { 0, 0, 0, 0, 0, 0, 0, 0 };
IvParameterSpec ivspec = new IvParameterSpec(iv);
System.out.println("k = " + k);
c.init(Cipher.DECRYPT_MODE, k, ivspec);
String dec = new String(c.doFinal(enc.getBytes()));
return dec;
}

[sirlink99]

Thanks that seems to have fixed the problem.