Simple MySql Injection

Ok, I liked to create websites and, at the beginning I didnt know almost anything about security, sessions, MySql Injection, I heard only about md5 and I thought that only crypting a password with md5 will be enough. But not!
First, I learn about sessions in PHP, then about "cleaning" a string and finally about MySql Injection. I remember that one day one of my friends tried to hack my databases and he failed... Why? Simple using of md5, sessions, and sanitizing my string.

So, first of all I give an example! If you have a simple script without md5 or anything, something like:

$username=$_POST[username];
$password=$_POST[password];
$login = mysql_query("SELECT * FROM user WHERE (username = $username) and (password =$password)");

if you try to input OR= as username and as pasword, youll access the database without any problem, with the username of the first user from table. Nice, right?

Ok... but now let try adding a function, like mysql_real_escape_string(). The example would look now like this:

$username=mysql_real_escape_string($_POST[username]);
$password=mysql_real_escape_string($_POST[password]);
$login = mysql_query("SELECT * FROM user WHERE (username = $username) and (password =$password)");
and if you input OR= youll have a surprise.
Ok, but now lets encrypt that login... so, Ill add sessions and md5.

And if you want the full login script that I used on my website and at all websites that I created, you can find it HERE.

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