Question

I have a very simple (rather stupid) question, I hope someone can clear my mind on this 🙂

I want to send an email to my site user once he clicks a button. This email will contain a link with the userID of a user in the link URL (as query param of a link).

Once the user clicks this email link, my server side code will parse and decrypt the userID query string key to get the user ID and perform some action on it.

I cannot use base64 encoding as it can be reversed and ‘hackers’ can get to know the real userID. I have to encrypt the ID but when I am using AES alogrithms for encryption, the encrypted text is not “understandable” by the browser, ie I cannot pass the encrypted userId text as a part of the URL because it contains un-encoded characters like “/” which the browser cannot by pass. One option I can think of is to base64 encode the encrypted text once I send it across via URL. Then I can bease64 decode and decyrpt it.

Is this approach better than using Uri.EscapeDataString() on the encyrpted text?

Answer 1

Use a one-way hash like SHA1 or MD5, and use JavaScript to send the values as encrypted. Then, if a hacker intercepts the request, they would only have the hashes and not the actual values. They could still send the hashes to login, though; one solution is to include a JavaScript parameter (generated via your server-side language) based on IP (but not possible for a hacker to find the formula for), and use it to salt the username and password hashes.

Then on server-side you would do (in PHP, in this case):

$ipHash = sha1("random" . $_SERVER['REMOTE_ADDR'] . "salt_here10381") // place this as a hidden element in the form and use it in the JavaScript to calculate the hash
$userHash = $_POST['userHash'];
$passwordHash = $_POST['passwordHash']
// TODO: Escape $ipHash, $userHash, $passwordHash
$results = mysqli->query("SELECT * FROM `users` WHERE SHA1(CONCAT('" . $ipHash . "', `user`)) ='$userHash' AND SHA1(CONCAT('" . $ipHash . "', `password`)) = " '$passwordHash'");

Then, if a hacker wanted to login with the hash and username they found, they would need the same IP of the user originally logging in whose credentials were intercepted.

Note that this assumes you have passwords stored in your database as plain-text, which you should never do.

For hashing with SHA1, on client-side, take a look at this.

To answer your specific question (I see I got a bit off topic, oops,) it would be acceptable to base64encode the hashes when you send them to the server. If possible, try to send it as POST data and save it in a cookie or session variable.