How do I safely store a password in a file??

Question

My program requires password to open some features. The password can be set by an administrator. My app stores the password in a file. But, if the file was deleted or damaged, the app loose the password. Another scenario is if the file was replaced with original file then the password will be empty. Any suggestions about storing a password in a file?

edited : My app has a feature. The feature is protected by a password that can be set by a admin (owner of the PC). Guest should enter password to disable that feature. OS : Windows

Answer 1

You can't protect the file from being deleted. In that case just don't allow any user to log in to your application (same applies if the password is empty).

If you store passwords in a file (or anywhere really) you should hash them (e.g. using md5 or sha1). So they can't be read in plaintext. To check the password during login just do (basic example in php):

$password = file_get_contents('password.file'); // Outside webroot of course
if(md5($_POST['password']) == $password) {
    // Login OK
}

Answer 2

What kind of program ? Which platform ? Windows, mac, linux, android ?

Files can always be deleted or replaced, one way or another. You can put it somewhere "safer" where the user can't find it easily, but if depends of the platform.