Padding Exception: Given final block not properly padded

Question

I am trying to encrypt and decrypt my file in which all my passwords are stored using AES.

The algorithm works fine on encryption part. But while decryption it throws the error

Message:Given final block not properly padded
javax.crypto.BadPaddingException: Given final block not properly padded
        at com.sun.crypto.provider.CipherCore.doFinal(CipherCore.java:966)
        at com.sun.crypto.provider.CipherCore.doFinal(CipherCore.java:824)
        at com.sun.crypto.provider.AESCipher.engineDoFinal(AESCipher.java:436)
        at javax.crypto.Cipher.doFinal(Cipher.java:2121)
        at SearchDoc.dec_file(SearchDoc.java:327)
        at SearchDoc.access$100(SearchDoc.java:52)
        at SearchDoc$2$1.actionPerformed(SearchDoc.java:227)
        at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
        at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
        at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
        at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
        at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
        at java.awt.Component.processMouseEvent(Unknown Source)
        at javax.swing.JComponent.processMouseEvent(Unknown Source)
        at java.awt.Component.processEvent(Unknown Source)
        at java.awt.Container.processEvent(Unknown Source)
        at java.awt.Component.dispatchEventImpl(Unknown Source)
        at java.awt.Container.dispatchEventImpl(Unknown Source)
        at java.awt.Component.dispatchEvent(Unknown Source)
        at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
        at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
        at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
        at java.awt.Container.dispatchEventImpl(Unknown Source)
        at java.awt.Window.dispatchEventImpl(Unknown Source)
        at java.awt.Component.dispatchEvent(Unknown Source)
        at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
        at java.awt.EventQueue.access$400(Unknown Source)
        at java.awt.EventQueue$3.run(Unknown Source)
        at java.awt.EventQueue$3.run(Unknown Source)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
        at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
        at java.awt.EventQueue$4.run(Unknown Source)
        at java.awt.EventQueue$4.run(Unknown Source)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
        at java.awt.EventQueue.dispatchEvent(Unknown Source)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
        at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
        at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
        at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
        at java.awt.EventDispatchThread.run(Unknown Source)

What is the problem here?

code:

//Starting decryption
try{
    byte[] key = c_key.getBytes("ISO-8859-1");
    key = Arrays.copyOf(key, 16); // use only first 128 bit
    //System.out.println(Arrays.toString(key));
    SecretKeySpec SecKey = new SecretKeySpec(key, "AES");
    Cipher AesCipher = Cipher.getInstance("AES");
    AesCipher.init(Cipher.DECRYPT_MODE, SecKey);

    BufferedReader breader = new BufferedReader(new FileReader("download/enc_"+file));
    String line;
    boolean bool = false;
    File f = new File(file);
    bool = f.createNewFile();
    if(bool==false){
        f.delete();
        bool = f.createNewFile();
    }
    PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter(file, true)));
    while ((line = breader.readLine()) != null){
         byte[] cipher=null;
         byte[] plain=null;

         cipher=line.getBytes("ISO-8859-1");
         plain=AesCipher.doFinal(cipher);

         out.println(new String(plain,"ISO-8859-1"));
    }
    out.close();
    return 1;
}
catch(Exception dcf){
    System.out.println("Message:"+dcf.getMessage());
    dcf.printStackTrace();
    return 0;
}

NEW AES CODE:

import java.security.*;
import javax.crypto.spec.SecretKeySpec;
import java.security.spec.InvalidKeySpecException;
import javax.crypto.*;
import sun.misc.*;

public class AESencrp {

     private static final String ALGO = "AES";
    private static final byte[] keyValue = 
        new byte[] { 'T', 'h', 'e', 'B', 'e', 's', 't',
'S', 'e', 'c', 'r','e', 't', 'K', 'e', 'y' };

public static String encrypt(String Data) throws Exception {
        Key key = generateKey();
        Cipher c = Cipher.getInstance(ALGO);
        c.init(Cipher.ENCRYPT_MODE, key);
        byte[] encVal = c.doFinal(Data.getBytes());
        String encryptedValue = new BASE64Encoder().encode(encVal);
        return encryptedValue;
    }

    public static String decrypt(String encryptedData) throws Exception {
        Key key = generateKey();
        Cipher c = Cipher.getInstance(ALGO);
        c.init(Cipher.DECRYPT_MODE, key);
        byte[] decordedValue = new BASE64Decoder().decodeBuffer(encryptedData);
        byte[] decValue = c.doFinal(decordedValue);
        String decryptedValue = new String(decValue);
        return decryptedValue;
    }
    private static Key generateKey() throws Exception {
        Key key = new SecretKeySpec(keyValue, ALGO);
        return key;
}

}

Answer 1

Using just AES as cipher instance does not declare how the final block is padded. This is why encryption and decryption may differ.

Use one of the following, concrete cipher instances instead (depending on your encryption mode):

AES/CBC/NoPadding
AES/CBC/PKCS5Padding
AES/ECB/NoPadding
AES/ECB/PKCS5Padding

You can find a list of the supported ciphers here