Detecting Dangerous Queries: A New Approach for Chosen Ciphertext Security

We present a new approach for creating chosen ciphertext secure encryption. The focal point of our work is a new abstraction that we call Detectable Chosen Ciphertext Security (DCCA). Intuitively, this notion is meant to capture systems that are not necessarily chosen ciphertext attack (CCA) secure, but where we can detect whether a certain query CT can be useful for decrypting (or distinguishing) a challenge ciphertext CT∗. We show how to build chosen ciphertext secure systems from DCCA security. We motivate our techniques by describing multiple examples of DCCA systems including creating them from 1-bit CCA secure encryption — capturing the recent Myers-shelat result (FOCS 2009). Our work identifies DCCA as a new target for building CCA secure systems.