Paper 2017/253

A Modular Security Analysis of EAP and IEEE 802.11

Chris Brzuska and Håkon Jacobsen

Abstract

We conduct a reduction-based security analysis of the Extensible Authentication Protocol (EAP), a widely used three-party authentication framework. EAP is often found in enterprise networks where it allows a client and an authenticator to establish a shared key with the help of a mutually trusted server. Considered as a three-party authenticated key exchange protocol, we show that the general EAP construction achieves a security notion we call 3P-AKE$^w$. The 3P-AKE$^w$ security notion captures the idea of \emph{weak forward secrecy} and is a simplified three-party version of the well-known eCK model in the two-pass variant. Our analysis is modular and reflects the compositional nature of EAP. Additionally, we show that the security of EAP can easily be upgraded to provide \emph{full} forward secrecy simply by adding a subsequent key-confirmation step between the client and the authenticator. In practice this key-confirmation step is often carried out in the form of a 2P-AKE protocol which uses EAP to bootstrap its authentication. A concrete example is the extremely common IEEE~802.11 protocol used in WLANs. In enterprise settings EAP is often used in conjunction with IEEE~802.11 in order to allow the wireless client to authenticate itself to a wireless access point (the authenticator) through some centrally administrated server. Building on our modular results for EAP, we get as our second major result the first reduction-based security result for IEEE~802.11 combined with EAP.