This snippet allows to encrypt and decrypt with mcrypt in PHP. Default algorithm and mode are Rijndael256 and CBC.

encryption_manager.php

<?php
// Author: Robertof
// You are free to use this, but please don't remove my name from the source. ty :3
class EncryptionManager
{
    private $algorithm;
    private $mode;
    private $cipher;
    
    public function __construct ($algorithm="rijndael-256", $mode="cbc")
    {
        $this->algorithm = $algorithm;
        $this->mode      = $mode;
        // open mcrypt module
        $this->cipher = mcrypt_module_open ($this->algorithm, "", $this->mode, "");
    }
    
    public function __destruct()
    {
        if (is_resource ($this->cipher))
            mcrypt_module_close ($this->cipher);
    }
    
    // NOTE: saving in a file just the output of the first element of the array
    //       returned isn't enough. You need to save the IV, otherwise
    //       the decrypt function won't work. I suggest you to do something like
    //       $iv . $enctext, and then a substr padding with the output
    //       of the function getIVSize() to get the IV and the enc. bindata.
    // Also note that if you are using ECB mode, IV isn't needed.
    // (IV = initialization vector)     
    public function encrypt ($text, $key1d, $key2d, $b64=true)
    {
        $cipher = $this->cipher;
        // create IV and get keysize
        $iv      = mcrypt_create_iv (mcrypt_enc_get_iv_size ($cipher), MCRYPT_DEV_URANDOM);
        $keysize = mcrypt_enc_get_key_size ($cipher);
        // create the key
        $key1 = base64_encode (hash ("sha256", $key1d, true));
        $key2 = base64_encode (hash ("sha256", $key2d, true));
        $key  = substr ($key1, 0, $keysize / 2) . substr ($key2, ( round ( strlen ($key2) / 2 ) ), $keysize / 2);
        $key  = substr ($key . $key1 . $key2 . $key1, 0, $keysize);
        // initialize encryption
        mcrypt_generic_init ($cipher, $key, $iv);
        // encrypt da shit
        // for padding reasons we add the original length to the encrypted text
        $enc = mcrypt_generic ($cipher, strlen ($text) . "|" . $text);
        mcrypt_generic_deinit ($cipher);
        return array (( $b64 ? base64_encode ($enc) : $enc ), $iv);
    }
    
    // You need to pass the returned IV from the encrypt function here,
    // otherwise the decryption won't work. Read the note above the encrpytion
    // function to learn more.
    public function decrypt ($data, $iv, $key1d, $key2d)
    {
        // get keysize
        $keysize = mcrypt_enc_get_key_size ($this->cipher);
        // generate key
        $key1 = base64_encode (hash ("sha256", $key1d, true));
        $key2 = base64_encode (hash ("sha256", $key2d, true));
        $key  = substr ($key1, 0, $keysize / 2) . substr ($key2, ( round ( strlen ($key2) / 2 ) ), $keysize / 2);
        $key  = substr ($key . $key1 . $key2 . $key1, 0, $keysize);
        // initialize decryption
        mcrypt_generic_init ($this->cipher, $key, $iv);
        $dec = mdecrypt_generic ($this->cipher, $data);
        // get original length (@ is to suppress 'undefined index' errors)
        @list ($len, $decshit) = explode ("|", $dec, 2);
        if (!$len || !$decshit || !is_numeric ($len) || (is_numeric ($len) && $len > strlen ($dec)))
            return false;
        $dec = substr ($decshit, 0, $len);
        mcrypt_generic_deinit ($this->cipher);
        return $dec;
    }
    
    public function getIVSize ()
    {
        return mcrypt_enc_get_iv_size ($this->cipher);
    }
}
?>