php - try catch is not giving output as expected

Hello I am using 2 functions for encryption and decryption

my Decryption function is as
follow

 function decrypt($string,
            $key = NULL) {

 // $key = 'this is new thign gor
            security';
 $string = base64_decode(base64_decode($string));
 $key =
            md5($key); //to improve variance
 /* Open module, and create IV */

            $td = mcrypt_module_open('des', '', 'cfb', '');

 $key =
            substr($key, 0, mcrypt_enc_get_key_size($td));
 $iv_size =
            mcrypt_enc_get_iv_size($td);
 $iv = substr($string, 0, $iv_size);

            $string = substr($string, $iv_size);

 /* Initialize encryption
            handle */
 if (mcrypt_generic_init($td, $key, $iv) != -1) {
 /*
            Encrypt data */
 $c_t = mdecrypt_generic($td, $string);

            mcrypt_generic_deinit($td);
 mcrypt_module_close($td);
 return
            $c_t;
 } //end if

            }

but in
this function if I pass string which is not actually Encryption then it is giving me
Notice undefined variable and does not give any output so thats why I add try catch blog
in to it as bellow

function
            decrypt($string, $key = NULL)
{



            try
 {
 $string =
            base64_decode(base64_decode($string));

 $key = md5($key); //to
            improve variance
 /* Open module, and create IV */
 $td =
            mcrypt_module_open('des', '', 'cfb', '');

 $key = substr($key, 0,
            mcrypt_enc_get_key_size($td));
 $iv_size =
            mcrypt_enc_get_iv_size($td);
 $iv = substr($string, 0, $iv_size);

            $string = substr($string, $iv_size);
 /* Initialize encryption handle
            */
 if (mcrypt_generic_init($td, $key, $iv) != -1)


            {
 /* Encrypt data */
 $c_t = mdecrypt_generic($td,
            $string);
 mcrypt_generic_deinit($td);

            mcrypt_module_close($td);
 return $c_t;
 } //end if
 }
            catch (Exception $exc)
 {
 echo
            $exc->getTraceAsString();

 }


 //
            $key = 'this is new thign gor security';
}
            

BUT again it struct
at same point and does not go to catch

Here I am
putting some string and
Key

encrypted string:
            dExXZStvRmV6WFR5NkE9PQ==

and KEY is :
            !1@2#3$4%5^6&7*8(9)0_-+=

You
can use this function Like this

$xyz =
            decrypt('dExXZStvRmV6WFR5NkE9PQ==','!1@2#3$4%5^6&7*8(9)0_-+=');

src="https://i.stack.imgur.com/zYxfC.jpg" alt="enter image description
here">