PHP crypt password

Question

I have two curiosities about encryption of passes, I have this code:

1- $mainpass = "test123";

$md5pass = md5($mainpass);
$sha1pass = sha1($md5pass);
$cryptpass = crypt($sha1pass, 'st');

echo ($cryptpass);

Whose output is: 'stSuGIR46GScI'.

But I do not understand why this (below) is not equal and the output is always changing:

$mainpass = "test123";
$cryptpass = crypt(sha1(md5($mainpass)));

echo ($cryptpass);

By my logic it would be equivalent.

2-And in checking and validating the password as it would change the code below that has only md5 to match the encryption done above (in the correct case)?

if(isset($_POST['username'], $_POST['password'])) {
$username = $_POST['username'];
$password = md5($_POST['password']);

Answer 1

Case 1:

In the first example, you are adding a Salt ('st') when calling the function crypt. I believe the problem is there, since it is the only visible difference. Change the second example to:

$cryptpass = crypt(sha1(md5($mainpass)), 'st');

Case 2:

Following the same logic, change the line on which the password is set:

$password = crypt(sha1(md5($_POST['password'])), 'st');