Back Channels Can Be Useful! - Layering Authentication Channels to Provide Covert Communication.

We argue the need for providing a covert back-channel communication mechanism in authentication protocols, discuss various practical uses for such a channel, and desirable features for its design and deployment. Such a mechanism would leverage the current authentication channel to carry out the covert communication rather than introducing a separate one. The communication would need to be oblivious to an adversary observing it, possibly as a man-in-the-middle. We discuss the properties that such channels would need to have for the various scenarios in which they would be used. Also, we show their potential for mitigating the effects of a number of security breaches currently occurring in these scenarios.