Stretching Cryptography to Foil Insider Threats

Dr Qiang Tang
Cornell University


Despite the laudatory history of the development of modern cryptography, applying cryptographic tools to reliably provide security and protect privacy in practice is notoriously difficult. Two fundamental assumptions have to be made in most of the scenarios. (1.) There is a secret key unknown to the adversary; (2.) The implementations faithfully realize the cryptographic algorithms; Unfortunately, we have witnessed real-world attack scenarios in which those two assumptions do not necessarily hold. In this talk, I will explain how we can stretch crypto to defend against those crippling insider attacks. First, I will use copyright protection as an application to exemplify how we may design cryptosystems to enforce (potentially dishonest) key owner accountability in a multi-recipient encryption scenario. In particular, I will introduce and construct a new cryptographic primitive called traitor deterring scheme (TDS) for this goal. The distinguishing characteristic of a TDS is that if a dishonest subscriber A distributes a pirate decoder, it would lead to the revelation of some collateral information of A. Furthermore, I will demonstrate how to use Bitcoin as the monetary deterrence to de-incentivize unauthorized re-distribution of pirate decoders. Second, I will discuss our recent progress on a new direction called cliptography: tackling the fundamental practical challenge of guaranteeing security without trust in underlying cryptographic implementations. Our results lay down the foundation of this emerging area. In particular, I will give an overview of this topic, and briefly discuss how we resolve the central problem of defending against subliminal channel attacks when using subverted randomized algorithms, and how we may build a parallel theory of crypto in this new setting.