RE: [saml-dev] SAML V2.0 Holder-of-Key Web Browser SSO Profile not immune against man-in-the-middle attack

["Scott Cantor" <cantor.2@osu.edu>]

> If we do not have any official (registered) certificate, MitM will always
be
> possible, as no session can ever be secured.

That's not true, even if there was such a thing as an "official"
certificate, which there isn't.
 
What prevents MitM is the use of a protocol that involves proof of
possession of the key between the client and the IdP, as opposed to
name/password. Who signed a certificate (if anybody) is completely
irrelevant.

Issues of anonymity are likewise orthogonal, other than to allow that with a
browser today, you're probably stuck using a single certificate (which could
be self-signed and contain an opaque DN) with both the IdP and SP. The lack
of privacy comes from the inability to easily use a different certificate
across sessions with the SP, so correlation becomes possible. This
compromises anonymity, but doesn't necessarily reveal your identity.

> Proposition: instead of stating that the key/certificate bind in the
> assertion and used with the SP must come from the TLS authentication to
the
> IdP, why not extending this to "a key/certificate sent to the IdP in a
> secure way"?

I'd just use the standard terminology, "a protocol establishing proof of
possession of the key".

-- Scott