如何正确解密javax.crypto加密的字符串

Question

I am getting the following error when trying to decrypted:

javax.crypto.IllegalBlockSizeException: Input length must be multiple of 16 when decrypting with padded cipher

Here is the encryption class I have implemented:

import java.io.UnsupportedEncodingException;
import java.security.InvalidKeyException;
import java.security.Key;
import java.security.NoSuchAlgorithmException;

import javax.crypto.BadPaddingException;
import javax.crypto.Cipher;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.spec.SecretKeySpec;

public class StringEncrypter {

    public static String encrypt(String key, String string, String algorithm) throws NoSuchPaddingException, NoSuchAlgorithmException, InvalidKeyException, BadPaddingException, IllegalBlockSizeException, UnsupportedEncodingException {
        Key aesKey = new SecretKeySpec(key.getBytes("UTF-8"), algorithm);
        Cipher cipher = Cipher.getInstance(algorithm);
        cipher.init(Cipher.ENCRYPT_MODE, aesKey);
        byte[] encrypted = cipher.doFinal(string.getBytes());
        return encrypted.toString();
    }

    public static String decrypt(String key, String encryptedString, String algorithm) throws NoSuchPaddingException, NoSuchAlgorithmException, InvalidKeyException, BadPaddingException, IllegalBlockSizeException, UnsupportedEncodingException {
        Key aesKey = new SecretKeySpec(key.getBytes("UTF-8"), algorithm);
        Cipher cipher = Cipher.getInstance(algorithm);
        cipher.init(Cipher.DECRYPT_MODE, aesKey);
        String decrypted = new String(cipher.doFinal(encryptedString.getBytes()));
        return decrypted;
    }
}

This is how I encrypted a string:

StringEncrypter.encrypt("0306868080306868", "ddd", "AES"); // [B@e19957c

When I attempt to decrypt the above encrypted string like this:

String decrypted = StringEncrypter.decrypt("0306868080306868", "[B@e19957c", "AES");

I get the illegalBlockSizeException .

What am I doing wrong above? How do I correctly decrypt an encrypted String?

Answer 1

You need to perform base 64 encoding decoding for your key and your ciphertext. There is a new Base64 class for this in Java 8. You cannot just store any byte in a string, not all bytes represent printable or even valid characters, and the output of a cipher is indistinguishable from random.

Besides that, the byte array "class" (represented by [B in Java) doesn't implement the toString method, which means you just get the print out of Object.toString , ie the class name [B and a human readable identifier to the object instance instead of the actual ciphertext.

Answer 2

You cannot use bytes (binary) as a String. it is not equivalent

You should convert it . Several manners. Base64 or Hexa, for example You with base64, it gives this:

import javax.xml.bind.DatatypeConverter ;

byte[] bt= ... // what you get

// Conversion B64
String encodedb64=DatatypeConverter.printBase64Binary(bt);

// CONVERSION base 64 => byte 
// base 64 => byte
byte [] byteArrayreverse=DatatypeConverter.parseBase64Binary(encodedb64);