PHP: Class for encryption / decryption

PHP: Class for encryption / decryption

class Encryption {

    const CYPHER = MCRYPT_RIJNDAEL_256;
    const MODE = MCRYPT_MODE_CBC;
    const KEY = 'anysecretkey';

    public function encrypt($plaintext) {
        $td = mcrypt_module_open(self::CYPHER, '', self::MODE, '');
        $iv = mcrypt_create_iv(mcrypt_enc_get_iv_size($td), MCRYPT_RAND);
        mcrypt_generic_init($td, self::KEY, $iv);
        $crypttext = mcrypt_generic($td, $plaintext);
        mcrypt_generic_deinit($td);
        return base64_encode($iv . $crypttext);
    }

    public function decrypt($crypttext) {
        $crypttext = base64_decode($crypttext);
        $plaintext = '';
        $td = mcrypt_module_open(self::CYPHER, '', self::MODE, '');
        $ivsize = mcrypt_enc_get_iv_size($td);
        $iv = substr($crypttext, 0, $ivsize);
        $crypttext = substr($crypttext, $ivsize);
        if ($iv) {
            mcrypt_generic_init($td, self::KEY, $iv);
            $plaintext = mdecrypt_generic($td, $crypttext);
        }
        return trim($plaintext);
    }

}

// Using example:
// $encrypted_string = Encryption::encrypt('2');
// $decrypted_string = Encryption::decrypt($encrypted_string);