issues trying to get openssl_encrypt to work - php

Question

I'm writing a class to handle encrypted data, essentially it will be used to encrypt data to be stored in a DB and then again to decrypt it on retrieval.
Here's what I've written:
class dataEncrypt {
private $encryptString;
private $decryptString;
private $encryptionMethod;
private $key;
public function __construct() {
/* IMPORTANT - DONT CHANGE OR DATA WILL DAMAGE */
$this->key = sha1('StringToHash');
// Set the encryption type
$this->encryptionMethod = "AES-256-CBC";
}
// Generate the IV key
private function generateIV() {
$ivSize = mcrypt_get_iv_size(MCRYPT_RIJNDAEL_256, MCRYPT_MODE_CBC);
return mcrypt_create_iv($ivSize, MCRYPT_RAND);
}
// Retrieve the key
private function retrieveKey() {
return $key;
}
// Encrypt a string
public function encryptString($string) {
// Return the encrypted value for storage
return openssl_encrypt($string, $this->encryptionMethod, $this->retrieveKey(), 0, $this->generateIV());
}
// Decrypt a string
public function decryptString($data) {
// return the decrypted data
return openssl_decrypt($data, $this->encryptionMethod, $this->retrieveKey(), 0, $this->generateIV());
return false;
}
}
I'm trying to encrypt a string before storing, and I get the following PHP warning:
Warning: openssl_encrypt(): IV passed is 32 bytes long which is longer than the 16 expected by selected cipher, truncating in /var/www/blahblah... on line xxx
I've googled this, Ive googled the IV functions, I can't find sweetheat on either. Any advice is welcomed here.
Thanks

Answer 1

I was able to get it working by passing MCRYPT_CAST_256 rather than MCRYPT_RIJNDAEL_256 into mcrypt_get_iv_size
Encrypt:
$iv_size = mcrypt_get_iv_size(MCRYPT_CAST_256, MCRYPT_MODE_CBC);
$iv = mcrypt_create_iv($iv_size, MCRYPT_RAND);
$encrypted = openssl_encrypt($string, "AES-256-CBC", $key, 0, $iv);
$encrypted = $iv.$encrypted;
Decrypt
$iv_size = mcrypt_get_iv_size(MCRYPT_CAST_256, MCRYPT_MODE_CBC);
$iv = substr($string, 0, $iv_size);
$decrypted = openssl_decrypt(substr($string, $iv_size), "AES-256-CBC", $key, 0, $iv);