A concise PHP reversible encryption function

Many times we need to encrypt and decrypt data. For example, some data needs to be saved in cookies, but the data cannot be easily obtained by users. At this time, we need to encrypt the data and save it in cookies until we need to use them. Decrypt again.

// Encrypt data and write it to cookie
$cookie_data = $this -> encrypt("nowamagic", $data);

$cookie = array(
 'name' => '$data ',
 'value' => $cookie_data,
 'expire' => $user_expire,
 'domain' => '',
 'path' => '/',
 'prefix' => ''
);
$this->input->set_cookie($cookie);

// Encryption
public function encrypt($key, $plain_text) {
 $plain_text = trim($plain_text);
 $ iv = substr(md5($key), 0,mcrypt_get_iv_size (MCRYPT_CAST_256,MCRYPT_MODE_CFB));
 $c_t = mcrypt_cfb (MCRYPT_CAST_256, $key, $plain_text, MCRYPT_ENCRYPT, $iv);
 return trim(chop(base64_encode($c_t )));
}

Decrypt when using:
if( isset($_COOKIE['data']) )
{
 //Use cookie to assign value to session
 $_SESSION['data'] = decrypt(" nowamagic", $_COOKIE['data']);
}

function decrypt($key, $c_t) {
 $c_t = trim(chop(base64_decode($c_t)));
 $iv = substr(md5( $key), 0,mcrypt_get_iv_size (MCRYPT_CAST_256,MCRYPT_MODE_CFB));
 $p_t = mcrypt_cfb (MCRYPT_CAST_256, $key, $c_t, MCRYPT_DECRYPT, $iv);
 return trim(chop($p_t));
}

The use of this reversible encryption function is recorded here.

PHP