As the capabilities of smartphones increase, users are beginning to rely on these mobile and ubiquitous platforms to perform more tasks. In addition to traditional computing tasks, people are beginning to use smartphones to interact with people they meet. Often this interaction begins with an exchange, e.g., of cryptographic keys. Hence, a number of protocols have been developed to facilitate this exchange. Unfortunately, those protocols that provide strong security guarantees often suffer from usability problems, and easy-to-use protocols may lack the desired security guarantees.