Ever been busted because you man in the middled software which does TLS properly and it alerted someone to your bad certificate? No more! Want to detect certain types of connection leaving your network, but can’t keep the IP blacklist up to date? This could be the answer. This talk includes an introduction to both TLS and man in the middle attacks, a walkthough on what TLS fingerprints contain, how to create your own fingerprints, how we use the fingerprints in several scenarios, a demo, and a discussion of implications and pitfalls. TLS provides transport security to all manner of connections from legitimate financial transactions to private conversations and malware calling home. The inability to analyze encrypted traffic protects its users, whether they are legitimate or malicious. This talk explores a technique for quickly and passively fingerprinting TLS clients and adapting our responses for the purposes of both attack and defense. Attackers can make automated decisions concerning when to man in the middle a connection and when to let the clients pass through silently, remaining stealthy. Defenders can gain insight into what is making encrypted connections within their networks without access to either endpoints or cryptographic keying material.”