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Re: Main mode using pre-shared keys
In fact, there is no identity protection in main mode with pre-shared
key for authentication. The peer's IP address has to be used to select
pre-shared key.
One solution is to re-define SKEYID. We may not use pre-shared key for
the generation of SKEYID. Instead, we can use the definition of SKEYID
for digital signature, i.e.
SKEYID = prf (Ni_b|Nr_b, g^xy)
We only need to use pre-shared key for authentication of IKE exchanges.
So we can replace HASH_I and HASH_R with AUTH_I and AUTH_R respectively
in the protocol, where
AUTH_I = prf (pre-shared-key, HASH_I)
AUTH_R = prf (pre-shared-key, HASH_R)
Jianying
On Wed, 27 Oct 1999, Qiang Zhang wrote:
> At 10:24 AM 10/27/99 -0700, CHINNA N.R. PELLACURU wrote:
> >RFC 2409
> >
> >5.4 Phase 1 Authenticated With a Pre-Shared Key
> >
> > Initiator Responder
> > ---------- -----------
> > HDR, SA -->
> > <-- HDR, SA
> > HDR, KE, Ni -->
> > <-- HDR, KE, Nr
> > HDR*, IDii, HASH_I -->
> > <-- HDR*, IDir, HASH_R
> >
> > When using pre-shared key authentication with Main Mode the key can
> > only be identified by the IP address of the peers since HASH_I must
> > be computed before the initiator has processed IDir. Aggressive Mode
> > allows for a wider range of identifiers of the pre-shared secret to
> > be used. In addition, Aggressive Mode allows two parties to maintain
> > multiple, different pre-shared keys and identify the correct one for
> > a particular exchange.
> >"
> >
> >
> >"identified by the IP address of the peers"
> >
> >Does this mean that the ID payload content must be an IP Address, and it
> >should be the same as the source IP address on the IKE packet that the
> >peers are using?
> >
> >If the source IP address on the packet is used to search the pre-shared
> >key, then we authenticate the peer, by the fact that the peer knows the
> >shared secret associated with the IP address he is using. Inspite of that,
> >is the RFC also advicing that we enforce, the ID payload content is the
> >source IP address that was used to search the shared secret?
>
> Chinna, notice that the HASHi computation HAS to use the peer-address to
> search the preshared secret thus I think at least in this circumstance, the
> ID payload won't work. Further one thing to worry about is that the
> source address is not trustable due to all kinds of IP routing scheme.
>
> This is something I think the WG should give a solution.
>
> Qiang
>
>
> >
> >If so, the confidentiality part of the Identity protection is not there,
> >when using pre-shared keys.
> >
> >What are the consequenses of not enforceing the above requirement? We are
> >authenticating the peer using the IP source address he is using, because
> >we search the pre-shared key based on it, but we accept his ID to be
> >anything.
> >
> >TIA, chinna
> >
> >chinna narasimha reddy pellacuru
> >s/w engineer
> >
> >
> >
>
>
References: