[p2p-hackers] Re: [rest-discuss] Re: RESTful authorization

[Laurian Gridinoc]

Hello

On 9/30/05, Lucas Gonze <lgonze at panix.com> wrote:
> Given that:
> The client has received at least one ID by secure means, and the client
> wants to fetch the corresponding representation.
> SSL/TLS is not available.
> The client has javascript.
> On the client:
> $salt = newRandomNumber();
> $hashed = hash(concat($id,$salt))
> $representation = GET /mapper?hashed=$hashed&salt=$salt
> [...]

The issue is how does the client know that the login page with the
above javascript was not modified by the MITM?

There is an ongoing discussion on webappsec at securityfocus.com about
"Must we authenticate login forms (using SSL?)?" see below a nice
issue about challenge-response and MITM:

---------- Forwarded message ----------
From: Rogan Dawes <discard at dawes.za.net>
Date: Sep 30, 2005 11:54 AM
Subject: Re: Must we authenticate login forms (using SSL?)?
Cc: Web Application Security <webappsec at securityfocus.com>

[...]

The core problem with any security mechanism that is implemented using
"stuff" (Javascript, Java applet, etc) that is downloaded from the
server that you are visiting is that any man in the middle attack can
simply remove that mechanism, and substitute it with their own.

e.g. My bank logon script performs an MD5 hash of the username and
password before sending it to the bank. The MITM tricks me to visiting
their own site, and just "proxies" the comms to the real site. However,
they strip out the MD5 hashing script,and replace it with an "identity"
function (i.e. the output is the same as the input). When the MITM
receives the form submission, it is trivial for them to extract the
username and password from the form, replace it with the MD5 hash
expected, and pass it on to the real bank.

I had started implementing/experimenting with using Secure Remote
Password (http://srp.stanford.edu/) for authentication to a secure web
site, with the idea that the password is never transmitted in clear, or
in a recoverable form. However, this stumbling point convinced me that
I'd be wasting my time!

One reason that SSL client certs offer real protection is that they are
not controllable by page content, and do not rely on something that
comes down from the site you are visiting.

Regards,

Rogan
---------- End Forwarded message ----------