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Re: HTTP Digest Integrity: Another look, in light of recent attacks
From: Dan Kaminsky <dan () doxpara com>
Date: Wed, 6 Jan 2010 08:59:37 +0100

I haven't been wildly impressed by Digest as implemented in browsers, but
it's a legitimate point that Digest has of at least *some* of the URI
embedded into it, so the TLS reneg attack can be somewhat mitigated by
leveraging that.  Empirically though, this is going to be a big pain in the
butt, not least of which is the dramatic change to the user experience.

Ultimately, far and away the most common forms of auth are cookie based,
with hidden variables being a close second.  In both of these the password
is accessible to the DOM.  So the raw material is there to add an integrity
layer to at least sensitive HTTPS transactions (everything is worthless for
HTTP).  But an advantage of your approach is that it applies generically to
all browser/site communication, including Javascript containers like <script
src> and <link rel=stylesheet>.  There's no way to register a hook that gets
triggered whenever a site hits a particular URI within a domain, to add the
validator, in JS.  It just happens in Digest.


On Wed, Jan 6, 2010 at 2:15 AM, Timothy D. Morgan <tmorgan () vsecurity com>wrote:


Hello,

Some of you may be interested in this short technical note which
includes some recent observations about TLS renegotiation and other
issues:
 http://www.vsecurity.com/download/papers/HTTPDigestIntegrity.pdf

Comments welcome,
tim



Introduction
============
Recent history has proven that web communications security is highly
lacking in redundancy.  That is, simple breaks in common protocols,
such as SSL/TLS or the authentication mechanisms which support it,
often lead to catastrophic gaps in security.  Recent examples of this
fragile architecture abound, and even when protocols and
implementations themselves are sound, research indicates browser user
interfaces continue to leave room for serious attacks.

This paper explores how the seldom-used HTTP digest authentication
protocol can be used to mitigate certain recent forms of attack,
including SSL/TLS renegotiation and some types of HTTP request
smuggling.

...

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Charter: http://lists.grok.org.uk/full-disclosure-charter.html
Hosted and sponsored by Secunia - http://secunia.com/

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