AES decrypt for j2me

Question

I read on this link AES Encryption/Decryption with Bouncycastle Example in J2ME about how to encrypt a string using AES as supplied by Bouncy Castle. The encryption method code works fine but decryption doesn't work.

Can anyone suggest how I can decrypt the encrypted string?

I've used the following code to test:

import com.codename1.util.Base64;
import org.bouncycastle.crypto.CipherParameters;
import org.bouncycastle.crypto.engines.AESEngine;
import org.bouncycastle.crypto.modes.CBCBlockCipher;
import org.bouncycastle.crypto.paddings.PaddedBufferedBlockCipher;
import org.bouncycastle.crypto.params.KeyParameter;
import org.bouncycastle.crypto.params.ParametersWithIV;

/**
 *
 * @author SAMUEL
 */
public class Tester {
    static  String strEnc = "Hi This is my String";
    final static String strPassword = "password12345678";

    private static byte[] cipherData(PaddedBufferedBlockCipher cipher, byte[] data)throws Exception
{
    int minSize = cipher.getOutputSize(data.length);
    byte[] outBuf = new byte[minSize];
    int length1 = cipher.processBytes(data, 0, data.length, outBuf, 0);
    int length2 = cipher.doFinal(outBuf, length1);
    int actualLength = length1 + length2;
    byte[] result = new byte[actualLength];
    System.arraycopy(outBuf, 0, result, 0, result.length);
    return result; 
}

private static byte[] decrypt(byte[] cipher, byte[] key, byte[] iv) throws Exception
{
    PaddedBufferedBlockCipher aes = new PaddedBufferedBlockCipher(new CBCBlockCipher(new AESEngine()));
    CipherParameters ivAndKey = new ParametersWithIV(new KeyParameter(key), iv);
    aes.init(false, ivAndKey);
    return cipherData(aes, cipher);
}

private static byte[] encrypt(byte[] plain, byte[] key, byte[] iv) throws Exception
{
    PaddedBufferedBlockCipher  aes = new PaddedBufferedBlockCipher(new CBCBlockCipher(new AESEngine()));
    CipherParameters ivAndKey = new ParametersWithIV(new KeyParameter(key), iv);
    aes.init(true, ivAndKey);
    return cipherData(aes, plain);
}


public static void main(String [] args) throws Exception{

    byte[] enc= encrypt(strEnc.getBytes(),"password12345678".getBytes(), "password12345678".getBytes());
    String encrypted =   Base64.encode(enc);
    System.out.println("Encrypted is:"+encrypted);
    byte[] dec= decrypt(encrypted.getBytes(),"password12345678".getBytes() , "password12345678".getBytes());        
    System.out.println("Decrypted file is:"+dec);
 }
}

Output is:

Encrypted is:sw0SrUIKe0DmS7sRd9+XMgtYg+BUiAfiOsdMw/Lo2RA=

And the exception stacktrace is:

Exception in thread "main" org.bouncycastle.crypto.DataLengthException: last block incomplete in decryption
    at org.bouncycastle.crypto.paddings.PaddedBufferedBlockCipher.doFinal(PaddedBufferedBlockCipher.java:281)
    at com.mycompany.myapp.Tester.cipherData(Tester.java:28)
    at com.mycompany.myapp.Tester.decrypt(Tester.java:40)
    at com.mycompany.myapp.Tester.main(Tester.java:57)

First of all, this question contains way too little information. Second, I wonder if you even read the comments below the answer you're pointing to. — Maarten Bodewes
it contains link to the main issue i am having.. i did and it works fine for crypting but i am having issues with decrypting that is why i am askin — San Ace
Eh, where is your code again? If you can edit your question I'd be happy to retract my close vote (these votes are mainly given if we cannot answer the question, not so much if we don't want to answer the question). — Maarten Bodewes
i am new to this site so i tried posting my code but for unknown reasons , i couldnt. but here is my code on codenameone forum... groups.google.com/forum/… — San Ace

Maarten Bodewes Maarten Bodewes · Accepted Answer · 2014-07-27T14:09:02

You are forgetting to base 64 decode the ciphertext before decryption. You should also create a new String from the decrypted bytes.

When encoding/decoding character strings, always specify the encoding explicitly, otherwise you will be using the platform default, which is not the same on each and every platform.

So use for instance new String(dec, "UTF-8") to recreate the plaintext, and specify "UTF-8" for each and every new String() and toBytes() method.

AES decrypt for j2me

1 Answers