Authentication in 802.11 LANs Using a Covert Side Channel

We present a covert side channel technique that uses the 802.11 MAC rate switching protocol as cover for covert authentication messages. Covert authentication prevents an attacker from knowing when a user is authenticating and protects user credentials from malicious software attacks. Similar to port knocking, a remote client sends authentication messages to an access point in order to access a protected service. The technique uses a one-time password algorithm to protect against replay attacks. We investigate how the covert side channel affects node throughput in mobile and non-mobile scenarios. We also investigate the covertness of the covert side channel using standardized entropy. The results show that the performance impact is minimal and increases slightly as the authentication frequency increases. We further show that we can authenticate with 100% accuracy with minimal impact on rate switching entropy.