Paper 2016/342 Original: eprint.iacr.org/2016/342 ↗

On the Selective Opening Security of Practical Public-Key Encryption Schemes

Abstract

We show that two well-known and widely employed public-key encryption schemes -- RSA Optimal Asymmetric Encryption Padding (RSA-OAEP) and Diffie-Hellman Integrated Encryption Scheme (DHIES), instantiated with a one-time pad, -- are secure under (the strong, simulation-based security notion of) selective opening security against chosen-ciphertext attacks in the random oracle model. Both schemes are obtained via known generic transformations that transform relatively weak primitives (with security in the sense of one-wayness) to IND-CCA secure encryption schemes. We also show a similar result for the well-known Fujisaki-Okamoto transformation that can generically turn a one-way secure public key encryption system and a one-time pad into a INDCCA-secure public-key encryption system. We prove that selective opening security comes for free in these transformations. Both DHIES and RSA-OAEP are important building blocks in several standards for public key encryption and key exchange protocols. The Fujisaki-Okamoto transformation is very versatile and has successfully been utilised to build efficient lattice-based cryptosystems. The considered schemes are the first practical cryptosystems that meet the strong notion of simulation-based selective opening (SIM-SO-CCA) security.