php - Can you encrypt an encrypted string over and over again? -

i wondering if can use md5 on , on again, or use sha1 on , on again, example:

$pass = md5($pass); $pass = sha1($pass); $pass = md5($pass); $pass = md5($pass); 

and still have work? encrypts encrypted string again , again because wanted make encrypted password system nobody can hack, , worried algorithm i'm creating work or not.?

if you're trying hash passwords, scrypt. don't use else, , don't roll own system.