Cryptology ePrint Archive: Report 2014/269

Chosen Ciphertext Security via Point Obfuscation

Takahiro Matsuda and Goichiro Hanaoka

Abstract: In this paper, we show two new constructions of chosen ciphertext secure (CCA secure) public key encryption (PKE) from general assumptions. The key ingredient in our constructions is an obfuscator for point functions with multi-bit output (MBPF obfuscators, for short), that satisfies some (average-case) indistinguishability-based security, which we call AIND security, in the presence of hard-to-invert auxiliary input. Specifically, our first construction is based on a chosen plaintext secure PKE scheme and an MBPF obfuscator satisfying the AIND security in the presence of computationally hard-to-invert auxiliary input. Our second construction is based on a lossy encryption scheme and an MBPF obfuscator satisfying the AIND security in the presence of statistically hard-to-invert auxiliary input. To clarify the relative strength of AIND security, we show the relations among security notions for MBPF obfuscators, and show that AIND security with computationally (resp. statistically) hard-to-invert auxiliary input is implied by the average-case virtual black-box (resp. virtual grey-box) property with the same type of auxiliary input. Finally, we show that a lossy encryption scheme can be constructed from an obfuscator for point functions (point obfuscator) that satisfies re-randomizability and a weak form of composability in the worst-case virtual grey-box sense. This result, combined with our second generic construction and several previous results on point obfuscators and MBPF obfuscators, yields a CCA secure PKE scheme that is constructed \emph{solely} from a re-randomizable and composable point obfuscator. We believe that our results make an interesting bridge that connects CCA secure PKE and program obfuscators, two seemingly isolated but important cryptographic primitives in the area of cryptography.

Category / Keywords: public-key cryptography / public key encryption, lossy encryption, key encapsulation mechanism, chosen ciphertext security, point obfuscation.

Original Publication (with major differences): IACR-TCC-2014

Date: received 16 Apr 2014

Contact author: t-matsuda at aist go jp

Available format(s): PDF | BibTeX Citation

Note: This is the full version of our paper in TCC 2014.

Version: 20140421:210602 (All versions of this report)

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