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Cybersecurity

CCA1 secure FHE from PIO, revisited

Biao Wang, Xueqing Wang, Rui Xue

Published Sep 25, 2018• 6 citations
Publisher

Abstract

Fully data using only public information. So far, most FHE schemes are CPA secure. In PKC 2017, Canetti et al. extended the generic transformation of Boneh, Canetti, Halevi and Katz to turn any multi-key identity-based FHE scheme into a CCA1-secure FHE scheme. Their main construction of multi-key identity-based FHE is from probabilistic indistinguishability obfuscation (PIO) and statistical trapdoor encryption. We show that the above multi-key identity-based FHE is not secure by giving an attack. Then we give a solution to avoid the attack and redesign a more succinct and efficient multi-key identity-based FHE scheme. Compared with the scheme of Canetti et al., ours has smaller secret key of one identity and more efficient homomorphic operations. Thus we obtain a more efficient CCA1 secure FHE scheme.

DOI
10.1186/s42400-018-0013-8

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Fully data using only public information. So far, most FHE schemes are CPA secure. In PKC 2017, Canetti et al. extended the generic transformation of Boneh, Canetti, Halevi and Katz to turn any multi-key identity-based FHE scheme into a CCA1-secure FHE scheme. Their main construction of multi-key identity-based FHE is from probabilistic indistinguishability obfuscation (PIO) and statistical trapdoor encryption. We show that the above multi-key identity-based FHE is not secure by giving an attack. Then we give a solution to avoid the attack and redesign a more succinct and efficient multi-key identity-based FHE scheme. Compared with the scheme of Canetti et al., ours has smaller secret key of one identity and more efficient homomorphic operations. Thus we obtain a more efficient CCA1 secure FHE scheme.
This paper proposes a generic construction of CCA-secure fully homomorphic encryption (FHE) scheme.First, we introduce a new primitive called multi-identity fully homomorphic encryption, which works in the multi-identity setting; that is, homomorphic evaluation can performed on ciphertexts created with different identities.Then, we propose an IND-sID-CPA secure multi-identity leveled FHE scheme over lattice.Finally, we present CCA-secure FHE from our proposed multi-identity FHE scheme and strongly EUF-CMA secure signature.The security analysis shows that our FHE scheme is CCA2-secure when the evaluation key is unavailable to the adversary, and remains CCA1-secure when the evaluation key is exposed in the standard model.
Multi-key fully homomorphic encryption (MKFHE), a generalization of fully homomorphic encryption (FHE), enables a computation over encrypted data under multiple keys. The first MKFHE schemes were based on the NTRU primitive, however these early NTRU based FHE schemes were found to be insecure due to the problem of over-stretched parameters. Recently, in the case of standard (non-multi key) FHE a secure version, called FINAL, of NTRU has been found. In this work we extend FINAL to an MKFHE scheme, this allows us to benefit from some of the performance advantages provided by NTRU based primitives. Thus, our scheme provides competitive performance against current state-of-the-art multi-key TFHE, in particular reducing the computational complexity from quadratic to linear in the number of keys.
Deterministic public-key encryption, encrypting a plaintext into a unique ciphertext without involving any randomness, was introduced by Bellare, Boldyreva, and O'Neill (CRYPTO 2007) as a realistic alternative to some inherent drawbacks in randomized public-key encryption. Bellare, Kiltz, Peikert and Waters (EUROCRYPT 2012) bring deterministic public-key encryption to the identity-based setting, and propose deterministic identity-based encryption scheme (DIBE). Although the construc- tions of chosen plaintext attack (CPA) secure DIBE scheme have been studied intensively, the construction of chosen ciphertext attack (CCA) secure DIBE scheme is still challenging problems. In this paper, we introduce the notion of identity-based all-but-one trapdoor functions (IB-ABO-TDF), which is an extension version of all-but-one lossy trapdoor function in the public-key setting. We give a instantiation of IB-ABO-TDF under decisional linear assumption. Based on an identity-based lossy trapdoor function and our IB-ABO-TDF, we present a generic construction of CCA-secure DIBE scheme.
We propose a generic construction that yields efficient identity-based encryption (IBE) schemes secure against chosen ciphertext attack (CCA) in the standard model. Our construction extends Kiltz et al.'s (Eurocrypt '09) method of constructing CCA-secure public-key encryption schemes via randomness extraction to the identity-based setting. The main idea of our construction is to transform ‘|ϵ1\epsilon _1ϵ1​|-almost |$\kappa ∣−entropic’andvalid/invalidciphertextindistinguishable(VI−IND)identity−basedhashproofsystemtotheonethatsatisfiesthestronger‘∣|-entropic’ and valid/invalid ciphertext indistinguishable (VI-IND) identity-based hash proof system to the one that satisfies the stronger ‘|∣−entropic’andvalid/invalidciphertextindistinguishable(VI−IND)identity−basedhashproofsystemtotheonethatsatisfiesthestronger‘∣\epsilon _2$|-universal’ and VI-IND property. This transformation is realized by a randomness extractor based on the 4-wise hash function. We demonstrate that our generic construction can produce CCA-secure IBE schemes whose efficiency is comparable with the most efficient but non-generic CCA-secure IBE schemes without random oracles in the literature.
Abstract. Fully homomorphic encryption (FHE) is a form of public-key encryption that enables arbitrary computation over encrypted data. The past few years have seen several realizations of FHE under differ-ent assumptions, and FHE has been used as a building block in many cryptographic applications. Adaptive security for public-key encryption schemes is an important se-curity notion proposed by Canetti et al. It is intended to ensure security when encryption is used within an interactive protocol and parties may be adaptively corrupted by an adversary during the course of the protocol execution. Due to the extensive applications of FHE to protocol design, it is natural to understand whether adaptively secure FHE is achievable. In this paper we show two contrasting results in this direction. First, we show that adaptive security is impossible for FHE satisfying the (stan-dard) compactness requirement. On the other hand, we show a construc-tion of adaptively secure FHE that is not compact, but that does achieve circuit privacy.
Multikey fully homomorphic encryption (MFHE) allows homomorphic operations between ciphertexts encrypted under different keys. In applications for secure multiparty computation (MPC) protocols, MFHE can be more advantageous than usual fully homomorphic encryption (FHE) since users do not need to agree with a common public key before the computation when using MFHE. In EUROCRYPT 2016, Mukherjee and Wichs constructed a secure MPC protocol in only two rounds via MFHE which deals with a common random/reference string (CRS) in key generation. After then, Brakerski et al. replaced the role of CRS with the distributed setup for CRS calculation to form a four round secure MPC protocol. Thus, recent improvements in round complexity of MPC protocols have been made using MFHE. In this paper, we go further to obtain round-efficient and secure MPC protocols. The underlying MFHE schemes in previous works still involve the common value, CRS, it seems to weaken the power of using MFHE to allow users to independently generate their own keys. Therefore, we resolve the issue by constructing an MFHE scheme without CRS based on LWE assumption, and then we obtain a secure MPC protocol against semi-malicious security in three rounds. We also define a new security notion “multikey-CPA security” to prove that a multikey ciphertext cannot be decrypted unless all the secret keys are gathered and our scheme is multikey-CPA secure.