IllegalBlockSizeException: last block incomplete in decryption in android

Question

Im developing android program which in i want to encrypt an string and then decrypt it as well. but i recieve this exception: javax.crypto.IllegalBlockSizeException: last block incomplete in decryption

I searched a lot but i couldn't find the answer.

this is my encrypt class which contains two methods Encrypt() and Decrypt():

    public class EncryptionClass {

public static SecretKey mainKey=null;



public static SecretKey GenerateKey() throws NoSuchAlgorithmException
{

    KeyGenerator keygenerator = KeyGenerator.getInstance("DES");
    SecretKey myDesKey = keygenerator.generateKey();
    return myDesKey;

    }


public static String Encrypt(String plainText) {

    String encryptedText = "";

    try {
        mainKey=GenerateKey();
            Cipher desCipher;

            // Create the cipher 
            desCipher = Cipher.getInstance("DES/ECB/PKCS5Padding");

            // Initialize the cipher for encryption
            desCipher.init(Cipher.ENCRYPT_MODE,mainKey);

            //sensitive information
            byte[] plainTextAsBytes =plainText.getBytes();
            Log.d("Text [Byte Format] : " , plainTextAsBytes.toString());
            Log.d("Text : " ,new String(plainTextAsBytes));

           // Encrypt the text
            byte[] cipherText = desCipher.doFinal(plainTextAsBytes);

            Log.d("Text Encryted : " ,cipherText.toString());

            encryptedText=cipherText.toString();

    }catch(NoSuchAlgorithmException e){
        Log.d("NoSuchAlgorithmException :", e.toString());
    }catch(NoSuchPaddingException e){
        Log.d("NoSuchPaddingException  :", e.toString());
    }catch(InvalidKeyException e){
        Log.d("InvalidKeyException:", e.toString());
    }catch(IllegalBlockSizeException e){
        Log.d("IllegalBlockSizeException:", e.toString());
    }catch(BadPaddingException e){
        Log.d("BadPaddingException:", e.toString());
    } 
    finally{

    }

    return encryptedText;

}

public static String Decrypt(String cipherText) {

    String decryptedText = "";

    try {

            Log.d("Decrypt MAin Key:",mainKey.getEncoded().toString());
            Cipher desCipher;

            // Create the cipher 
            desCipher = Cipher.getInstance("DES/ECB/PKCS5Padding");

            // Initialize the cipher for encryption
            desCipher.init(Cipher.DECRYPT_MODE,mainKey);


           // Encrypt the text

            byte[] cipherTextBytes=cipherText.getBytes();
            byte[]  plainText= desCipher.doFinal(cipherTextBytes);

            Log.d("Text Decryted : " ,plainText.toString());

            decryptedText=plainText.toString();

    }catch(NoSuchAlgorithmException e){
        Log.d("NoSuchAlgorithmException :", e.toString());
    }catch(NoSuchPaddingException e){
        Log.d("NoSuchPaddingException  :", e.toString());
    }catch(InvalidKeyException e){
        Log.d("InvalidKeyException:", e.toString());
    }catch(IllegalBlockSizeException e){
        Log.d("IllegalBlockSizeException:", e.toString());
    }catch(BadPaddingException e){
        Log.d("BadPaddingException:", e.toString());
    } 
    finally{

    }


    return decryptedText;
}

}

and this is my main activity where i call methods:

            public void onClick(View arg0) {

            String ct=EncryptionClass.Encrypt("the text to encrypt");
            Log.d("Cipher Text", ct);

            String pt=EncryptionClass.Decrypt(ct);
            Log.d("Plain Text", pt);

        }

any help really appreciate. Best Regards,

You searched a lot? I find that hard to believe. A simple Google search for exactly that exception returns hundreds of results for me. — Simon
– Simon, Commented Feb 11, 2014 at 20:31
yes that's right.there are alot of posts but i couldn't solve my problem reading them. — Elmira Frhn
– Elmira Frhn, Commented Feb 11, 2014 at 21:04

Yolanda Ruiz · Accepted Answer · 2014-02-11 20:32:13Z

2

cipherText.toString() will not work as you think as the byte array can contain arbitrary bytes. Some of them will be lost or mangled in the conversion and the resulting ciphertext cannot be decrypted.

Keep the byte[] around and use that to feed the Decrypt, or convert the bytes to Base64.

answered Feb 11, 2014 at 20:32

Yolanda Ruiz

7164 silver badges7 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Elmira Frhn Over a year ago

thanks a lot for your answer.How should i convert bytes to Base64?

user207421 Over a year ago

cipherText.toString() won't work at all, regardless of the content of the array.

user207421 · Accepted Answer · 2014-02-11 21:11:14Z

0

Ciphertext is binary, and String isn't a container for binary data. Pass the ciphertext around as byte[], not String.
cipherText.toString() is just byte[].toString(), and that doesn't give you a String containing its contents anyway, just a class name and object hashCode. But when you attend to (1) the problem will disappear anyway.

answered Feb 11, 2014 at 21:11

user207421

312k45 gold badges324 silver badges493 bronze badges

Collectives™ on Stack Overflow

IllegalBlockSizeException: last block incomplete in decryption in android

2 Answers 2

2 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related