A Formal Analysis of IEEE 802.11’s WPA2: Countering the Kracks Caused by Cracking the Counters

Summary

The IEEE 802.11 WPA2 protocol is widely used across the globe to protect network connections. The protocol, which is specified on more than three-thousand pages and has received various patches over the years, is extremely complex and therefore hard to analyze. In particular, it involves various mechanisms that interact with each other in subtle ways, which offers little hope for modular reasoning. Perhaps because of this, there exists no formal or cryptographic argument that shows that the patches to the core protocol indeed prevent the corresponding attacks, such as, e.g., the notorious KRACK attacks from 2017. In this work, we address this situation and present an extensive formal analysis of the WPA2 protocol design. Our model is the first that is detailed enough to detect the KRACK attacks; it includes mechanisms such as the four-way handshake, the group-key handshake, WNM sleep mode, the data-confidentiality protocol, and their complex interactions. Our analysis provides the first security argument, in any formalism, that the patched WPA2 protocol meets its claimed security guarantees in the face of complex modern attacks.