/**
* Decrypts the given input data.
*
* @param in data to decrypt
* @param k secret key
* @param a encryption algorithm
* @param ivl initialization vector length
* @return decrypted data
* @throws NoSuchAlgorithmException ex
* @throws NoSuchPaddingException ex
* @throws InvalidKeyException ex
* @throws InvalidAlgorithmParameterException ex
* @throws IllegalBlockSizeException ex
* @throws BadPaddingException ex
*/
private static byte[] decrypt(final byte[] in, final byte[] k, final byte[] a, final int ivl)
throws NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException,
InvalidAlgorithmParameterException, IllegalBlockSizeException, BadPaddingException {
final SecretKeySpec keySpec = new SecretKeySpec(k, string(a));
final Cipher cipher = Cipher.getInstance(string(ALGN.get(lc(a))));
// extract iv from message beginning
final byte[] iv = substring(in, 0, ivl);
final IvParameterSpec ivspec = new IvParameterSpec(iv);
cipher.init(Cipher.DECRYPT_MODE, keySpec, ivspec);
return cipher.doFinal(substring(in, ivl, in.length));
}
/**
* Encrypts the given input data.
*
* @param in input data to encrypt
* @param k key
* @param a encryption algorithm
* @param ivl initialization vector length
* @return encrypted input data
* @throws InvalidKeyException ex
* @throws InvalidAlgorithmParameterException ex
* @throws NoSuchAlgorithmException ex
* @throws NoSuchPaddingException ex
* @throws IllegalBlockSizeException ex
* @throws BadPaddingException ex
*/
private static byte[] encrypt(final byte[] in, final byte[] k, final byte[] a, final int ivl)
throws InvalidKeyException, InvalidAlgorithmParameterException, NoSuchAlgorithmException,
NoSuchPaddingException, IllegalBlockSizeException, BadPaddingException {
final Cipher cipher = Cipher.getInstance(string(ALGN.get(lc(a))));
final SecretKeySpec kspec = new SecretKeySpec(k, string(a));
// generate random iv. random iv is necessary to make the encryption of a
// string look different every time it is encrypted.
final byte[] iv = new byte[ivl];
// create new random iv if encrypting
final SecureRandom rand = SecureRandom.getInstance("SHA1PRNG");
rand.nextBytes(iv);
final IvParameterSpec ivspec = new IvParameterSpec(iv);
// encrypt/decrypt
cipher.init(Cipher.ENCRYPT_MODE, kspec, ivspec);
final byte[] t = cipher.doFinal(in);
// initialization vector is appended to the message for later decryption
return concat(iv, t);
}