Exception pad block corrupted using AESLight from BouncyCastle

Question

Hi all!
I�m trying to encrypt and decrypt using AESLight from Bouncy Castle to provide cryptographi to my mobile application. I encrypt the text with no problems, and sometimes i decrypted with no problems to!
But, with some messages i got the follow exception:
org.bouncycastle.crypto.InvalidCipherTextException: pad block corrupted
     at org.bouncycastle.crypto.paddings.PKCS7Padding.padCount(Unknown Source)
     at org.bouncycastle.crypto.paddings.PaddedBufferedBlockCipher.doFinal(Unknown Source)
     at softcomex.sfw2go.server.seguranca.TranslatorAESLight.processMsg(TranslatorAESLight.java:40)
     at softcomex.sfw2go.server.Waiter.sendMessageToClient(Waiter.java:251)
     at softcomex.sfw2go.server.Waiter.run(Waiter.java:211)My class that uses AESLight:
public TranslatorAESLight (byte[] key, boolean cripto)
          this.keyAES = new byte[16];
          System.arraycopy(key, 0, this.keyAES, 0, key.length>16?16:key.length);
          this.cripto = cripto;
     }And, when I have to encrypt/decrypt i call the method processMsg:
public byte[] processMsg (String msg)
          byte[] msgReturn = null;
          int length = 0;
          BlockCipher engine = new AESLightEngine();
          BufferedBlockCipher cipher = new PaddedBufferedBlockCipher(new CBCBlockCipher(engine));
          KeyParameter key = new KeyParameter(keyAES);
          cipher.init(cripto, key);
          msgReturn = new byte[cipher.getOutputSize(msg.getBytes().length)];
          length = cipher.processBytes(msg.getBytes(), 0, msg.getBytes().length, msgReturn, 0);
          try {
               cipher.doFinal(msgReturn, length);
          } catch ( Exception e) {
               e.printStackTrace();
          return msgReturn;
     }Please, there is something wrong with this code?
Thanks.

Answer 1

I believe sabre150 has posted a good link in this
forum explaining why this doesn't work, but the
bottom line is that you cannot create a String from
an arbitrary byte array.I can't remember a single definitive reference (my memory is suspect these days) but I do have an example that shows why one should not try to convert bytes to a string using new String(bytes).
I got the basics of the Levenshtein algorithm on this forum somewhere but I can't find it. If anyone can give me the reference I will acknowledge it in the code.
import java.util.*;
import java.text.*;
import java.nio.charset.*;
public class BytesToStringErrorsDemonstration
    public static int levenshteinDistance( byte[] s, byte[] t)
        int n = s.length;
        int m = t.length;
        if (n == 0) return m;
        if (m == 0) return n;
        int[][] d = new int[n + 1][m + 1];
        for ( int i = 0; i <= n; d[0] = i++ );
for ( int j = 1; j <= m; d[0][j] = j++ );
for ( int i = 1; i <= n; i++ )
byte sc = s[ i-1 ];
for (int j = 1; j <= m;j++)
int v = d[i-1][j-1];
if ( t[ j-1 ] != sc ) v++;
d[i][j] = Math.min( Math.min( d[i-1][ j] + 1, d[i][j-1] + 1 ), v );
return d[n][m];
public static void main(String[] args)
// Create a set of random bytes
Random random = new Random();
byte[] originalBytes = new byte[2048];
random.nextBytes(originalBytes);
// Go through each supported character set
SortedMap<String,Charset> availableCharsets = Charset.availableCharsets();
for (String encoding : availableCharsets.keySet())
System.out.print(encoding);
// Turn the bytes into a String
String string;
try
string = new String(originalBytes, encoding);
catch (Exception e)
System.out.println(" - unable to convert bytes to String");
continue;
// Get back the bytes from the string
byte[] recoveredBytes;
try
recoveredBytes = string.getBytes(encoding);
catch (Exception e)
System.out.println(" - unable to convert String back to bytes");
continue;
// Test the original against the recovered
boolean areSame = Arrays.equals(originalBytes, recoveredBytes);
if (areSame)
System.out.println(" - no differences");
else
final DecimalFormat percentFormatter = new DecimalFormat("0.0");
int levenshteinCount = levenshteinDistance(originalBytes, recoveredBytes);
System.out.println(" - differences - Levenshtein count = " + levenshteinCount + " (" + percentFormatter.format(100.0 * levenshteinCount / originalBytes.length) + " %)");