javax.crypto.BadPaddingException for AES when encrypting and decrypting multiple times

[Mridul Dinakar]

Hi,

I am trying to encrypt and decrypt a message(String) using a given key string. For that, two seperate methods (one for encrypt and the other for decrypt) were called and when these methods are called from my applicaion. I am getting the below exception while decrypting. The encryption and decryption operations are working properly for the first time.Again if I call the methods with different message and key value it is throwing the below exception.

Exception:
javax.crypto.BadPaddingException: Given final block not properly padded
at com.sun.crypto.provider.CipherCore.doFinal(CipherCore.java:811)
at com.sun.crypto.provider.CipherCore.doFinal(CipherCore.java:676)
at com.sun.crypto.provider.AESCipher.engineDoFinal(AESCipher.java:313)
at javax.crypto.Cipher.doFinal(Cipher.java:2086)

I don't think that, there is a problem with data. Because using the same data (key and message) when I try to call the encrypt/decrypt methods it is working properly. Also if I call the methods from my application for the first time, it will work fine. Please help me to solve the issue......

[Tim Moores]

Impossible to say without seeing the encryption/decryption code.

[Mridul Dinakar]

Tim Moores wrote:Impossible to say without seeing the encryption/decryption code.

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Code is as shown below. I want to encrypt using specific key. So I am not using any specific key generator. Key is passed as string

import java.math.BigInteger;
import javax.crypto.Cipher;
import javax.crypto.spec.SecretKeySpec;

/**
 *
 * @author User
 */
public class EncryptDecrypt {

    public static String asHex(byte buf[]) {
        StringBuffer strbuf = new StringBuffer(buf.length * 2);
        int i;
        for (i = 0; i < buf.length; i++) {
            if (((int) buf[i] & 0xff) < 0x10) {
                strbuf.append("0");
            }

            strbuf.append(Long.toString((int) buf[i] & 0xff, 16));
        }

        return strbuf.toString();
    }

    public static byte[] hexStringToByteArray(String s) {
        int len = s.length();
        byte[] data = new byte[len / 2];
        for (int i = 0; i < len; i += 2) {
            data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4)
                    + Character.digit(s.charAt(i + 1), 16));
        }
        return data;
    }

    public String encrypt(String message, String key) {
        String encryptedString = "";
        try {
            System.err.println(" String to encrypt:" + message);
            System.err.println(" key :" + key);
            String s = new BigInteger(key).toString(2);
            Integer intArr[] = new Integer[16];
            int startIndex = 0, endIndex = 7;
            int diff = 128 - s.length();
            if (diff > 0) {
                while (diff != 0) {
                    s = s + 0;
                    diff = diff - 1;
                }
            }
            for (int i = 0; i < 16; i++) {
                intArr[i] = Integer.parseInt(String.valueOf(s.substring(startIndex, endIndex)), 2);
                startIndex = startIndex + 8;
                endIndex = endIndex + 8;
            }
            byte b1 = intArr[0].byteValue();
            byte b2 = intArr[1].byteValue();
            byte b3 = intArr[2].byteValue();
            byte b4 = intArr[3].byteValue();
            byte b5 = intArr[4].byteValue();
            byte b6 = intArr[5].byteValue();
            byte b7 = intArr[6].byteValue();
            byte b8 = intArr[7].byteValue();
            byte b9 = intArr[8].byteValue();
            byte b10 = intArr[9].byteValue();
            byte b11 = intArr[10].byteValue();
            byte b12 = intArr[11].byteValue();
            byte b13 = intArr[12].byteValue();
            byte b14 = intArr[13].byteValue();
            byte b15 = intArr[14].byteValue();
            byte b16 = intArr[15].byteValue();
            byte[] raw = {b1, b2, b3, b4, b5, b6, b7, b8, b9, b10, b11, b12, b13, b14, b15, b16};
            SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");
            Cipher cipher = Cipher.getInstance("AES");
            cipher.init(Cipher.ENCRYPT_MODE, skeySpec);
            byte[] encrypted = cipher.doFinal(message.getBytes());
            encryptedString = asHex(encrypted);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return encryptedString;
    }

    public String decrypt(String encryptedString, String key) {
        String originalString = "";
        System.err.println(" encryptedString :" + encryptedString);
        System.err.println(" key :" + key);
        try {
            String s = new BigInteger(key).toString(2);
            Integer intArr[] = new Integer[16];
            int startIndex = 0, endIndex = 7;

            int diff = 128 - s.length();
            if (diff > 0) {
                while (diff != 0) {
                    s = s + 0;
                    diff = diff - 1;
                }
            }
            for (int i = 0; i < 16; i++) {
                intArr[i] = Integer.parseInt(String.valueOf(s.substring(startIndex, endIndex)), 2);
                startIndex = startIndex + 8;
                endIndex = endIndex + 8;
            }
            byte b1 = intArr[0].byteValue();
            byte b2 = intArr[1].byteValue();
            byte b3 = intArr[2].byteValue();
            byte b4 = intArr[3].byteValue();
            byte b5 = intArr[4].byteValue();
            byte b6 = intArr[5].byteValue();
            byte b7 = intArr[6].byteValue();
            byte b8 = intArr[7].byteValue();
            byte b9 = intArr[8].byteValue();
            byte b10 = intArr[9].byteValue();
            byte b11 = intArr[10].byteValue();
            byte b12 = intArr[11].byteValue();
            byte b13 = intArr[12].byteValue();
            byte b14 = intArr[13].byteValue();
            byte b15 = intArr[14].byteValue();
            byte b16 = intArr[15].byteValue();
            byte[] raw = {b1, b2, b3, b4, b5, b6, b7, b8, b9, b10, b11, b12, b13, b14, b15, b16};
            SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");
            Cipher cipher = Cipher.getInstance("AES");
            cipher.init(Cipher.DECRYPT_MODE, skeySpec);
            byte[] encrypted;
            encrypted = hexStringToByteArray(encryptedString);
            byte[] original = cipher.doFinal(encrypted);
            originalString = new String(original);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return originalString;
    }
}

[Tim Moores]

Looks complicated. Any particular reason you're using the asHex and hexStringToByteArray methods instead of somethingmore standard like base-64 encoding? Lots of tested libraries are available for that, so you'd know the problem isn't with that part.