A Secure Session Key Negotiation Scheme in WPA2-PSK Networks

Wi-Fi Protected Access II Pre-Shared Key (WPA2-PSK) is a hot way to wireless security in public Wi-Fi networks. It works on a pre-configured passphrase shared with all stations in the same Wi-Fi network. Session keys (e.g., Pairwise Transient Key, PTK) between stations and the access point (AP) are derived from the passphrase. The WPA2-PSK networks can authenticate external stations, however, they fail to guarantee confidential communication if internal attackers own the passphrase in the network since all stations derive their PTK using the same passphrase. To prevent internal stations from eavesdropping the PTK, a secure session key negotiation scheme in WPA2-PSK Networks (SSKNS) is proposed. We introduce a temporary session key (TSK), which is encrypted using elliptic curve cryptography (ECC) and exchanged securely between the station and the AP in the Wi-Fi association process. Through AES algorithm with TSK, the station encrypts its own nonce used to generate the unique PTK in the 4-way process. Our scheme neither modifies the legacy process related to PTK generation nor adds plethoric overhead on excessive protection of all messages. Security analysis and simulations performed in NS-3 demonstrate that by consuming a few computation overheads, SSKNS can effectively provide security level, compared with the existing schemes.

I. Introduction

Wi-Fi now permeates our daily lives, enabling devices (e.g., desktops, laptops, smartphones) to provide wireless high-speed Internet and network connection. Wi-Fi Protected Access (WPA) is a network security technology based on WiFi, which provides authentication and encryption services. Although Wi-Fi Protected Access 3 (WPA3) was released by the Wi-Fi Alliance in2018, Wi-Fi Protected Access 2 (WPA2) is still the most commonly used security protocol in the market so far [1]. There are two security modes of WPA2, WPA2-Personal (aka WPA2-PSK) and WPA2-Enterprise. Both use a robust encryption method called AES-CCMP [2] to protect data transmitted over the air. The main difference between these two security modes exists in the authentication access stage. WPA2-Enterprise uses IEEE 802. 1X that needs a particular authentication server [3]. WPA2-PSK uses a preshared key and is designed for home users without an enterprise authentication server [4]. Most public Wi-Fi networks such as hotels, coffee shops, tend to adopt WPA2-PSK since it is more accessible to deploy and use than WPA2-Enterprise.