Public Key Cryptography PKC 2015
We study simulation based, selective opening security against chosen ciphertext attacks (SIM SO CCA security) for public key encryption (PKE) In a selective opening, chosen ciphertext attack (SOCCA) an adversary has access to a decryption oracle, sees a vector of ciphertexts, adaptively chooses to open some of them, and obtains the corresponding plaintexts and random coins used in the creation of the ciphertexts. The SIM SO CCA notion captures the security of unopened ciphertexts with respect to probabilistic polynomial time (ppt) SO CCA adversaries in a semantic way: what a ppt SO CCA adversary can compute can also be simulated by a ppt simulator with access only to the opened messages. Building on techniques used to achieve weak deniable encryption and non committing encryption, Fehr et al. (Eurocrypt 2010) presented an approach to constructing SIM SO CCA secure PKE from extended hash proof systems (EHPSs) collision resistant hash functions and an information theoretic primitive called Cross Authentication Codes (XACs) We generalize their approach by introducing a special type of Key Encapsulation Mechanism (KEM) and using it to build SIMSO CCA secure PKE. We investigate what properties are needed from the KEM to achieve SIM SO CCA security. We also give three instantiations of our construction. The first uses hash proof systems, the second relies on the n Linear assumption, and the third uses indistinguishability obfuscation (iO) in combination with extracting, puncturable PseudoRandom Functions in a similar way to Sahai and Waters (STOC 2014) Our results establish the existence of SIM SO CCA secure PKE assuming only the existence of one way functions and iO. This result further highlights the simplicity and power of iO in constructing different cryptographic primitives. c (c) International Association for Cryptologic Research 2015 J. Katz (Ed. PKC 2015, LNCS 9020, pp. 3 26, 2015. DOI: 10.1007/978 3 662 46447 2 1 4 S. Liu and K.G. Paterson
Lecture Notes in Computer Science