Hello,
Here are some comments on this draft for IETF LC. There are some
editorial nits, some errors that might be considered editorial but
there is a serious issue with the Security Considerations that I think
needs addressing.
I'll start with the security issue since it's the most serious (and
some may stop reading after getting to the editorial complaints).
Issue in Security Considerations:
In IKEv2 both sides present identities in the form of an ID payload.
EAP also has an identity exchange that is not useful for authentication
so EAP methods typically include their own, separate, identity
exchange. In many cases that identity is in a protected channel from
the EAP peer to the EAP server. When the EAP server is not co-located
with the IKEv2 implementation (i.e. EAP is offloaded to a separate
server) the identities that are actually authenticated are unknown
and/or unverified.
Section 6.2 mentions this from the client's point-of-view-- "after
the client has verified the AUTH payload sent by the IKEv2 gateway,
it knows that it is talking to SOME gateway trusted by the home AAA
server, but not which one." This is used as a segue to the "lying
NAS problem", which I have note below is not really solved so this
problem isn't really addressed properly.
But the problem is worse. The point-of-view of the gateway is never
mentioned. The gateway may know some anonymous identity, or an
identity that is colored or obfuscated that is useful only by the
EAP server to determine which EAP method to offer. It does not know
what the real client identity is. The identity that gets authenticated
is unknown to the gateway!
Unfortunately, it is the authenticated identity that the gateway must
use to look up an entry in the IPsec Security Policy Datbase (see
RFC 4301) that says what kind of security (bypass, drop, protect
rules, etc) to apply to the client's packets. It is therefore not
possible to properly support RFC 4301 when using this EAP-only
method of authentication.
Furthermore, the only identity available to the gateway can be
forged so the client can achieve more favorable access to the
protected network (a more "generous" security policy) than the
gateway would have given it had it known its _real_ identity.
I think there has to be a top-down analysis of RFC 4301 and how this
scheme impacts it. Each part of RFC 4301 that cannot be supported
or can only be supported in a limited manner must be spelled out and
the impact of the lack, or limit, of support has to be presented in
this draft's Security Considerations so a reader/implementer knows
what he's getting into if he decides to implement this scheme.
I would advise a DISCUSS on this draft until this has been worked out.
Errors:
- the draft states "IEEE 802.11i uses EAP without any PKI for
authenticating the WLAN access points." That is just plain wrong.
IEEE 802.11 is agnostic about particular EAP methods but requires
they provide mutual authentication and key generation. The Wi-Fi
Alliance certifies IEEE 802.11 implementations (and the EAP methods
they use). Of the EAP methods certified for use in IEEE 802.11--
EAP-TLS, EAP-TTLS w/MSCHAPv2, PEAPv0 w/MSCHAPv2, PEAPv1 w/GTC,
and EAP-SIM-- only EAP-SIM does not require a PKI. Having been
involved in that particular industry for most of the past decade
I can assure the authors that PKIs of some sort are used in most
every deployment of IEEE 802.11i. I have yet to see a pure EAP-SIM
deployment anywhere.
- in section 6.2 the draft mentions the "lying NAS problem" and says
that "EAP methods that provide what is called 'connection binding'
or 'channel binding' transport some identity or identities of the
gateway (or WLAN access point/NAS)." The table in section 4 lists
EAP methods that supposedly support "channel binding" but none of
methods with a "yes" in that column do what section 6.2 says.
The closest is EAP-SAKE (RFC 4763) which includes identities in a
MIC but that won't solve the "lying NAS problem" and RFC 4763 even
says, "EAP-SAKE does not claim channel binding" (so the table in
section 4 is wrong). The others provide a protected channel but don't
say how this can be used to actually solve the "lying NAS problem".
The draft really needs to say that this problem has not been solved
yet and remains an issue that must be taken into account if someone
decides to implement this scheme.
Editorial nits:
- this draft really does not justify its existence well at all. I
know the WG decided to pursue this work item but the reasoning
around that decision does not come through in this draft.
The introduction says that "[P]ublic key signatures and shared
secrets are not flexible enough to meet the requirements of
many deployment scenarios." OK, so there's some unnamed credential
needed (probably a token card or some such). This is handled using
the existing EAP support in IKEv2 so why is this scheme being defined?
Then the draft mentions as justification that "deployment of a PKI
is required" and "in many cases this is not realistic." If that's
the case then why are EAP methods that require a PKI listed in
the table of acceptable EAP methods for this technique?
In section 2 the draft says "Offering EAP based authentication has
the advantage that multiple different authentication and key
exchange protocols are available with EAP with different security
properties (such as strong password based protocols, protocols
offering user identity confidentiality and many more)." OK, fine
but all that is easily satisfied with the existing EAP support in
IKEv2 so why is this scheme being defined?
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