How to send password securely via HTTP using Javascript in absence of HTTPS?

The very basic issue all developers face: Whenever user submits the form, the password is sent via network and it must be protected. The site I develop for doesn't have HTTPS. Neither does the owner want to buy a SSL certificate, nor is he interested in a self-signed one. So I want to protect the password sent via HTTP using Javascript when submitting form.

To eager downvoters: How to send password securely over HTTP? DOES NOT give any sensible solution and I am in another situation.

If I use MD5, one can reverse that password string. What about nonce/HMAC? Any available Javascript library for that? Or do you have any suggestion/hint to tackle? Thanks in advance!

Solution 1:

There is no way to send a password securely that the user can verify without SSL.

Sure, you can write some JavaScript that will make a password secure for over-the-wire transmission through hashing or public-key-encryption. But how can the user be sure that the JavaScript itself has not been tampered with by a man-in-the-middle before it reached them, to send the password to an attacker instead of the site, or even just compromise the security of the algorithm? The only way would be for them to be expert programmers and have them inspect every line of your page and script to ensure it was kosher before typing the password. That is not a realistic scenario.

If you want passwords to be safe from man-in-the-middle attacks, you must buy an SSL cert. There is no other way. Get used to it.

If I use MD5, one can reverse that password string.

No... not trivially at least. Whilst MD5 has attacks against it, it's a hashing algorithm and thus unreversable. You would have to brute-force it.

But again, a man-in-the-middle attacker doesn't need to look at your MD5s. He can simply sabotage the JavaScript you send the user to make the MD5s.

Solution 2:

The solution here is to not send the password at all. Use challenge/response.

In the original form include a large block of random text along with a key. Store the original random text in the session based on key on the server. When the client submits the form, use JS to hash the random text and password together. Then send the username, key, and hashed random text to the server. DO NOT send the password. On the server, use the key to lookup the original random text, perform the same hashing operation with the stored password. If the server-hashed value matches the client hashed value, then you know the client entered the right password without ever sending the password to the server.

Whether the password is right or not, expire the key and random text so each are one-time-use.

Solution 3:

If you REALLY want to deep-dive into this, look at the Diffie-Hellman key exchange which was created to "allow two parties that have no prior knowledge of each other to jointly establish a shared secret key over an insecure communications channel"

I'm not a cryptography expert though, so I don't fully know if it's really secure if an attacker has both the Client (JavaScript source code) and the transport mechanism (Packet sniffer)

Solution 4:

You can use a javascript RSA implementation to encrypt the password before sending. (Here is an example of RSA In Javascript.)

But I believe both this one and using a hash function will be vulnerable to replay attacks. So, be careful.