Rijndael 256-bit encryption/decryption throws an error - php

Question

I've got the following class.
<?php
/**
* Cypher Class
*/
class Cipher
{
/**
* SHA256 Encrypted Key
* #var string
*/
private $encryptedKey;
/**
* Initial vector
*
* Used to seed the encryption string
*
* #var string
*/
private $initVector;
/**
* Constructor
* #param boolean|string $personalKey Holds the personal key to use in encryption
*/
public function __construct($personalKey = false)
{
// $config = configuration::getInstance();
if (false === $personalKey) {
return false;
} else {
$key = $personalKey;
}
$this->encryptionKey = hash('sha256', $key, TRUE);
$size = mcrypt_get_iv_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CFB);
$this->initVector = mcrypt_create_iv($size, MCRYPT_DEV_URANDOM);
}
/**
* Encrypt a string
* #param mixed $input Data to encrypt
* #return string Encrypted data
*/
public function encrypt($input)
{
return array(
'salt' => base64_encode($this->initVector),
'encrypted_value' => base64_encode(mcrypt_encrypt(
MCRYPT_RIJNDAEL_256,
$this->encryptionKey,
$input,
MCRYPT_MODE_CFB,
$this->initVector
)));
}
/**
* Decrypt string
* #param string $input Encrypted string we are going to decrypt
* #param string $salt Encrypted salt used to decrypt
* #return string Decrypted output
*/
public function decrypt($input, $salt)
{
return trim(mcrypt_decrypt(MCRYPT_RIJNDAEL_256, $this->encryptionKey, base64_decode($input), MCRYPT_MODE_CFB, $salt));
}
}
Both my IV and encrypted string are 16 bytes but for some reason PHP gives me the following error:
Warning: mcrypt_encrypt(): The IV parameter must be as long as the blocksize in C:\xampp\htdocs\public\cipher\Cipher.php on line 58
I am not really a star in encryptions and so I was wondering if one of you good people could help me out.

Answer 1

The size of an IV is related to the block size of the cipher. So whatever you choose as the block size must be used as the length of the IV.
Rijndael supports block sizes of 128, 160, 192, 224, and 256 bits. If you use MCRYPT_RIJNDAEL_128 then you are using the 128-bit block size (which matches AES). If you use MCRYPT_RIJNDAEL_256 then your block-size is twice as large.
So, you must decide which block size you want to use and ensure your code consistently refers to the same MCRYPT_RIJNDAEL_* constant.
I assume the website is giving you an error because it's expecting a 16-byte block size (as per AES).