BadPaddingException during decryption in java

Question

I am new java to encryption. Trying to implement something light weight to encrypt a string and store it somewhere and de-crypt it back before using.

With some web search I came up with this for encryption and decryption.

   public static String base64Encode(byte[] bytes)
    {
        return new BASE64Encoder().encode(bytes);
    }

   public static byte[] base64Decode(String property) throws IOException
    {
        return new BASE64Decoder().decodeBuffer(property);
    }


    public static String encrypt(String mystring) throws GeneralSecurityException, UnsupportedEncodingException
       {
        SecretKeyFactory keyFactory = SecretKeyFactory.getInstance("PBEWithMD5AndDES");
        SecretKey key = keyFactory.generateSecret(new PBEKeySpec(mystring.toCharArray()));
        Cipher pbeCipher = Cipher.getInstance("PBEWithMD5AndDES");
        pbeCipher.init(Cipher.ENCRYPT_MODE, key, new PBEParameterSpec(SALT, 20));
        return base64Encode(pbeCipher.doFinal(mystring.getBytes("UTF-8")));
        }

    public static String decrypt(String estring) throws GeneralSecurityException, IOException
        {
        SecretKeyFactory keyFactory = SecretKeyFactory.getInstance("PBEWithMD5AndDES");
        SecretKey key = keyFactory.generateSecret(new PBEKeySpec(estring.toCharArray()));
        Cipher pbeCipher = Cipher.getInstance("PBEWithMD5AndDES");
        pbeCipher.init(Cipher.DECRYPT_MODE, key, new PBEParameterSpec(SALT, 20));
        return new String(pbeCipher.doFinal(base64Decode(estring)), "UTF-8");
        }

I see that encryption worked but I saw a padding related exception in the decryption part, from the doFinal block. Here it is...

 encrypted string:zdrtgOKfkZMgpCOflr1ILQ==  -> Encrypted String
 exceptionjavax.crypto.BadPaddingException: Given
 final block not properly padded -> Exception from the doFinal block.

Seems like when I encrypted it, I need to do some kind of padding.

Can any one tell me what went wrong and how can it be fixed?

Thanks

Tas

Steve C · Accepted Answer · 2016-08-30 05:25:37Z

You are using password based encryption here. This means that the encryption key itself is based upon a password. You must use the same password for both encryption and decryption.

private static char[] ENCRYPTION_PASSWORD
     = "some password populated by configuration".toCharArray();

public static String encrypt(String mystring)
  throws GeneralSecurityException, UnsupportedEncodingException {
    SecretKeyFactory keyFactory = SecretKeyFactory.getInstance("PBEWithMD5AndDES");
    SecretKey key = keyFactory.generateSecret(new PBEKeySpec(ENCRYPTION_PASSWORD));
    Cipher pbeCipher = Cipher.getInstance("PBEWithMD5AndDES");
    pbeCipher.init(Cipher.ENCRYPT_MODE, key, new PBEParameterSpec(SALT, 20));
    return DatatypeConverter
        .printBase64Binary(pbeCipher.doFinal(mystring.getBytes("UTF-8")));
}

public static String decrypt(String string)
  throws GeneralSecurityException, IOException {
    SecretKeyFactory keyFactory = SecretKeyFactory.getInstance("PBEWithMD5AndDES");
    SecretKey key = keyFactory.generateSecret(new PBEKeySpec(ENCRYPTION_PASSWORD));
    Cipher pbeCipher = Cipher.getInstance("PBEWithMD5AndDES");
    pbeCipher.init(Cipher.DECRYPT_MODE, key, new PBEParameterSpec(SALT, 20));
    return new String(pbeCipher.doFinal(DatatypeConverter
                                           .parseBase64Binary(estring)), "UTF-8");
}

Note also the use of javax.xml.bind.DatatypeConverter for base64 operations. No need to write your own or use third parties these days.

anacron · Accepted Answer · 2016-08-30 05:09:27Z

0

You will need to first decode your input to the decrypt method.

Call the base64Decode method and the estring parameter in your decrypt method.

That should do it.

answered Aug 30, 2016 at 5:09

anacron

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Comments

sampathlk · Accepted Answer · 2016-08-30 06:15:53Z

0

Change your code ,

SecretKey key = keyFactory.generateSecret(new PBEKeySpec(mystring.toCharArray()));

to

SecretKey key = keyFactory.generateSecret(new PBEKeySpec("PASSWORD".toCharArray(), SALT, 20));

edited Aug 30, 2016 at 6:15

answered Aug 30, 2016 at 6:07

sampathlk

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