A Unified Methodology For Constructing Public-Key Encryption Schemes Secure Against Adaptive Chosen-Ciphertext Attack

We introduce a new methodology for achieving security against adaptive chosen-ciphertext attack (CCA) for public-key encryption schemes, which we call the oblivious decryptors model. The oblivious decryptors model generalizes both the two-key model of Naor and Yung, as well the Cramer–Shoup encryption schemes. The key ingredient in our new paradigm is Sahai’s notion of Simulation-Sound NIZK proofs. Our methodology is easy to use: First, construct an encryption scheme which satisfies the “bare” oblivious-decryptors model: This can be done quite easily, with simple proofs of security. Then, by adding a Simulation-Sound NIZK proof, the scheme becomes provably CCA-secure. Note that this paradigm allows for the use of efficient special-purpose Simulation-Sound NIZK proofs, such as those recently put forward by Cramer and Shoup. We also show how to present all known efficient (provably secure) CCA-secure public-key encryption schemes as special cases of our model.