RE: issue of initiating client auth for parallel SSL sessionids

Hi Peter,

 

It may help me to understand what you're proposing if you could describe the
request flow using the HTTP semantics. I'm having a bit of trouble
understanding your proposal, and that's making it hard to evaluate the
security implications. Something like the simple sequence diagram at [1]
would help greatly.

 

My concern is that you're proposing that a user agent perform the WebID auth
sequence over HTTPS/SSL, but then continue the browsing session through
unsecured HTTP. This seems to defeat any guarantee of secure user
authentication, which is why I'm wanting to make sure I've understood
correctly.

 

Two example attacks that would make such a proposal untenable are the
injection of malicious scripts [2] or session hijacking [3]. The requests
received over HTTP cannot be assured of the WebID accessing them, since the
connection may be MITMed, and likewise, requests received over HTTPS may
have been initiated by malicious script running downloaded via HTTP.

 

Further, the idea of maintaining two independent SSL session IDs for a
single domain is not something most user agents presently support (Firefox
and Chrome come to mind). So while WebID by leveraging SSL client auth with
a single identity is something that most every modern browser supports, and
they will cache the (relatively expensive, computationally and network) TLS
client auth stage, maintaining parallel sessions to the same domain, with
distinct identities (smart card/eid and WebID) will most likely require
browser vendors to change their networking implementations in order to
support WebID. This is in addition to the WebID-specific provisions such as
..crt handling/specialized Accept headers that seem to be proposed here. I
would think that such requirements would prevent any widespread adoption of
WebID, because it will require browser vendors to adopt it in order to be
widely deployed, but browser vendors typically aren't likely to adopt
WebID-specific modifications unless/until it is widely deployed.

 

In order for WebID (or any really any Web-based authentication mechanism,
for that matter) to be used securely, the requests, including the initial
one [4] [5], need to happen over a secure connection (such as SSL). Once
that connection is established, then the requests need to continue to happen
over that security association if you're going to assume that identity
remains correct. That is, you can only assume the WebID user is "logged
in"/"authenticated" if/while every request originates over the HTTPS session
that the WebID was provided over.

 

If you're concerned about the desire to provide authn/authz via multiple
certificates, then it should be possible with TLS secure renegotiation [6].
Because each subsequent renegotiation is secured/protected by the previous
security establishment, a server could request multiple forms of
authentication by sending a HelloRequest, and in the new handshake,
requesting a different set of CAs in the CertificateRequest. Under such a
scenario, a user can prove their possession of a WebID private key in one
handshake and then, using that channel, prove their possession of a smart
card-based private key in a subsequent renegotiation handshake. While such a
scenario works at a TLS level, it will still likely require modifications to
user agents to fully support, as it requires careful thought about the user
experience, it has the benefit of accomplishing the same goal without being
WebID-specific.

 

Thanks,

Ryan

 

[1] http://www.w3.org/wiki/Foaf%2Bssl

[2]
https://www.blackhat.com/presentations/bh-usa-09/SOTIROV/BHUSA09-Sotirov-Att
ackExtSSL-PAPER.pdf

[3] http://en.wikipedia.org/wiki/Firesheep

[4] http://www.thoughtcrime.org/software/sslstrip/

[5] http://en.wikipedia.org/wiki/HTTP_Strict_Transport_Security

[6] http://tools.ietf.org/html/rfc5746

 

From: public-xg-webid-request@w3.org [mailto:public-xg-webid-request@w3.org]
On Behalf Of peter williams
Sent: Saturday, February 26, 2011 8:21 PM
To: public-xg-webid@w3.org
Subject: issue of initiating client auth for parallel SSL sessionids

 

Because of the history of FOAF+SSL, we tend to see demos in which folks goto
a site with http, and then use a login button - guarding a protected region
of the site (or protected modes).

 

I think we need something more general.

 

As one browsers page index.html, should there by a file X referenced (call
it .crt), let the browser connect to its server using https (for that file
GET, only). Presumaly, if browser knows the mime type of .crt, it populates
the accept header with something suitable.

 

What I want is that the validation agent only kick off when it receives a
particular accept header ( induced by a containing page reference that
forced population of that accept header on the resource retrieval attempt).

 

Webid protocol would then run (and setup an SSL sessionid), but https would
not be protecting the connections to other page elements. As one moves
through a site, the SSL sessionid (due to webid protocol) can still guard
access using an authorization logic.

 

What this allows is both classical client authn (using smartcards, in DOD
land) and webid client authn. Now, it easy for the site to maintain 2
distinct SSL sessions, 1 with CA's controlling the selection of certs (which
hits the smartcard/eID) and 1 which does leverages webid.

 

Those SSL connections on the same site supervised by the smartcard/eID SSL
sessionid obviously leverage smartcard/eID's crypto,  doing SSL connections
that offer channel encryption using the *assured* crypto of the card (and
applying CA-based certg chaining authn .merely to protect the channel's
encryption SA). 

 

Those SSL connections on the same site supervised by the webid SSL sessionid
are distinct, influencing "login" authentication and "web sessions" -
driving an authorization engine (perhaps based on federated social network
conceptions)