javax.crypto.BadPaddingException: error

Question

I am trying to run a simple encryption/decryption program. I am getting a padding exception. There must be something hidden that I am not aware. I basically encrypted a string write it to a file, read it back, and decrypted it. The original encrypted array was decrypted without a problem. I compared the original encrypted array with the array read back from the file, they were identical from what I can see. The buffer from the file does not work, so there must be something difference. I don't know what to do.

import java.security.*;  
import java.security.spec.InvalidKeySpecException;  
import javax.crypto.Cipher;  
import javax.crypto.spec.SecretKeySpec;  

import java.io.*;  

public class sample  
{  
   private static String _algo = "AES";  
   private static byte[] _key = new byte[16];  

   public static byte[] encrypt (String val) throws Exception  
   {  
      Key key = new SecretKeySpec (_key, _algo);  
      Cipher c = Cipher.getInstance (_algo);  

      c.init (Cipher.ENCRYPT_MODE, key);  

      byte[] encode = c.doFinal (val.getBytes());  

      return encode;  
   }  

   public static String decrypt (byte[] val) throws Exception    
   {  
      Key key = new SecretKeySpec (_key, _algo);  
      Cipher c = Cipher.getInstance (_algo);  

      c.init (Cipher.DECRYPT_MODE, key);  

      byte[] decode = c.doFinal (val);  

      String decodeStr = new String (decode);  

      return decodeStr;  
   }  

   public static void main (String[] args) throws Exception  
   {  
      String str = "Good bye cruel world";  

      //  
      // get password from command line  
      //  
      _key = args[0].getBytes();  

      byte[] encodeArray = sample.encrypt (str);  

      //  
      // write encrypted array to file  
      //  
      FileOutputStream os = new FileOutputStream ("data");  
      os.write (encodeArray);  
      os.close();  

      //  
      // decode and print out string  
      //  
      String decodeStr = sample.decrypt (encodeArray);  
      System.out.println ("decodeStr = " + decodeStr);  

      //  
      // read back encrypted string  
      byte[] buffer = new byte[64];  
      FileInputStream is = new FileInputStream ("data");  
      is.read (buffer);  
      is.close();  

      decodeStr = sample.decrypt (buffer);  
      System.out.println ("decodeStr = " + decodeStr);  
   }  
}  

Output:

java sample 1234567890123456  
decodeStr = Good bye cruel world  
Exception in thread "main" javax.crypto.BadPaddingException: Given final block not   properly padded  
        at com.sun.crypto.provider.SunJCE_f.b(DashoA13*..)  
        at com.sun.crypto.provider.SunJCE_f.b(DashoA13*..)  
        at com.sun.crypto.provider.AESCipher.engineDoFinal(DashoA13*..)  
        at javax.crypto.Cipher.doFinal(DashoA13*..)  
        at sample.decrypt(sample.java:32)  
        at sample.main(sample.java:70)  

Answer 1

The problem is that the byte buffer with a size of 64, which you are reading the file into, is too big. Change it to 32.

Or use the length of the file like this:

byte[] buffer = new byte[(int)new File("data").length()];