Welcome to the resource topic for 2002/163
Title:
Man-in-the-Middle in Tunnelled Authentication Protocols
Authors: N. Asokan, Valtteri Niemi, Kaisa Nyberg
Abstract:Recently new protocols have been proposed in IETF for protecting
remote client authentication protocols by running them within a
secure tunnel. Examples of such protocols are PIC, PEAP and EAP-TTLS.
One goal of these new protocols is to enable the migration from legacy
client authentication protocols to more secure protocols, e.g., from
plain EAP type to, say, PEAP. In the new drafts, the security of
the subsequent session credentials are based only on keys derived
during the unilateral authentication where the network server is
authenticated to the client. Client authentication is mentioned as an
option in PEAP and EAP-TTLS, but is not mandated. Naturally, the PIC
protocol does not even offer this option, because the goal of PIC is
to obtain credentials that can be used for client authentication.
In addition to running the authentication protocols within such tunnel
it should also be possible to use them in legacy mode without any
tunnelling so as to leverage the legacy advantages such as widespread
use. In this paper we show that in practical situations, such a mixed
mode usage opens up the possibility to run a man-in-the-middle attack
for impersonating the legitimate client. For those well-designed
client authentication protocols that already have a sufficient level
of security, the use of tunnelling in the proposed form is a step
backwards because they introduce a new vulnerability.
The problem is due to the fact that the legacy client authentication
protocol is not aware if it is run in protected or unprotected mode.
We propose to solve the discovered problem by using a cryptographic
binding between the client authentication protocol and the protection
protocol.
ePrint: https://eprint.iacr.org/2002/163
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