RE: comments on draft-houseley-aaa-key-mgmt-07.txt
2007-02-19 00:23:33
Hi Yoshi,
-----Original Message-----
From: Yoshihiro Ohba [mailto:yohba(_at_)tari(_dot_)toshiba(_dot_)com]
Sent: Sunday, February 18, 2007 7:26 PM
To: Narayanan, Vidya
Cc: Dondeti, Lakshminath; Sam Hartman;
bernarda(_at_)microsoft(_dot_)com; Dan Harkins; ietf(_at_)ietf(_dot_)org
Subject: Re: comments on draft-houseley-aaa-key-mgmt-07.txt
On Sat, Feb 17, 2007 at 11:43:38PM -0800, Narayanan, Vidya wrote:
Yes, the problem of an authenticator providing different
identities to
the peer and the server is the typical channel binding
problem and can
be detected by simply doing a protected exchange of the identity
between the peer and server. When such a discrepancy is detected,
then, keys won't be handed out or if the identity is part
of the key
derivation, then, it will result in a key mismatch anyway. Hence,
there is no problem there.
In my understanding, Dan's claim is that the server is unable to
detect that an authenticator is claiming an incorrect
identity and by
virtue of that, if the authenticator claims the false
identity to both
the peer and the server, a key will be provided to the
authenticator
and that will match the key that the peer derives, even if the
identity was part of the key derivation. This is the problem that I
have detailed in my earlier email and I belive that can be resolved
with the text I proposed.
Yes, this is a problem that should not happen. If this
happens, the peer may send out data that is specific to ISP2
to the lying authenticator (which is actually an ISP1 entity
but claiming itself to be an ISP2 entity) that is not
supposed to see the ISP2-specific data.
Going back to your proposed text:
"It is RECOMMENDED that the key transport protocol be able to detect
impersonation. When it is not feasible to guarantee that, every key
handed out from the server to an entity for a given peer MUST be
different from every other key handed out for a given peer."
I think that detection of impersonation is part of the
"Authenticate all parties" *requirement* (not a recommendation).
I don't think it is a "requirement" - and the reason I believe that is
due to the second sentence in that text above. This is what I tried to
explain in much greater detail in my first response to Sam on this
thread. As long as no two keys distributed from the server are the same,
even to the same perceived identity, there is nothing that a lying
entity can do to sessions with other entities. So, as long as a solution
satisfies that criteria, it is not a MUST to detect impersonation. But,
I do agree that it would be much better if the detection was done by the
key transport mechanism - hence, I think "RECOMMENDED" is appropriate :)
By the way, recent discussion on 3-party key distribution
over HOKEY mailing list made me think more about the
following text in Section 5 (I don't know whether this is
part of Dan's comment as I did not see his original comment
on this mailing list):
"
The authenticator is also a trusted party. The authenticator is
trusted not to distribute keying material provided by the
AAA server
to any other parties. If the authenticator uses a key derivation
function to derive additional keying material, the authenticator is
trusted to distribute the derived keying material only to the
appropriate party that is known to the peer, and no other party.
When this approach is used, care must be taken to ensure that the
resulting key management system meets all of the principles in this
document, confirming that keys used to protect data are to be known
only by the peer and authenticator.
"
I understand that the authenticator is a trusted party for
the EAP/AAA server. On the other hand, I don't think we can
say that it is a trusted party for the peer before running
EAP, unless the link between the peer and the authenticator
is already secured or the peer and the authenticator have
already a shared key to believe before running EAP.
I agree. In my understanding, the text above is talking about the fact
that the authenticator is a trusted party to the server and because the
peer trusts the server, it trusts the authenticator after it has proven
possession of the right key. So, in that sense, the text seems fine to
me.
Vidya
Regards,
Yoshihiro Ohba
Regards,
Vidya
-----Original Message-----
From: Lakshminath Dondeti [mailto:ldondeti(_at_)qualcomm(_dot_)com]
Sent: Saturday, February 17, 2007 9:36 AM
To: Sam Hartman
Cc: Narayanan, Vidya; bernarda(_at_)microsoft(_dot_)com; Dan Harkins;
ietf(_at_)ietf(_dot_)org
Subject: Re: comments on draft-houseley-aaa-key-mgmt-07.txt
Sam,
The problem of an entity in the middle giving disparate
information
to the peer and the server is in fact easier to solve than the
problem Vidya summarized. The disparate information problem has
been described in the EAP Keying Framework document and elsewhere
too.
To my understanding, we are beyond that point in the
discussion in
HOKEY and considering the new case of the entity in the
middle lying
to both sides and attempting to get a key that another
entity in the
middle is supposed to get.
Let me put it this way, both issues are considered problems to
address/solve in this case.
regards,
Lakshminath
Sam Hartman wrote:
Vidya, I found the model you proposed didn't fit what Dan
was talking
about very well. In particular, Dan wants to focus on problems
resulting from the fact that the name of the authenticator used
between the peer and the authenticator may be different
than the name
of the authenticator used between the authenticator and the AAA
server. That distinction did not figure prominently enough in
your argument that I could tell whether you and Dan are talking
about the
same thing nor whether I could even tell if I agreed with you.
I'd recommend refocusing your model on this distinction; I
think once you
do we may well make significant progress on discussing a
long-standing
issue.
--Sam
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