International Association for Cryptologic Research

International Association
for Cryptologic Research

CryptoDB

Fabrice Benhamouda

Affiliation: IBM Research

Publications

Year
Venue
Title
2019
PKC
Decentralizing Inner-Product Functional Encryption
Multi-client functional encryption (MCFE) is a more flexible variant of functional encryption whose functional decryption involves multiple ciphertexts from different parties. Each party holds a different secret key and can independently and adaptively be corrupted by the adversary. We present two compilers for MCFE schemes for the inner-product functionality, both of which support encryption labels. Our first compiler transforms any scheme with a special key-derivation property into a decentralized scheme, as defined by Chotard et al. (ASIACRYPT 2018), thus allowing for a simple distributed way of generating functional decryption keys without a trusted party. Our second compiler allows to lift an unnatural restriction present in existing (decentralized) MCFE schemes, which requires the adversary to ask for a ciphertext from each party. We apply our compilers to the works of Abdalla et al. (CRYPTO 2018) and Chotard et al. (ASIACRYPT 2018) to obtain schemes with hitherto unachieved properties. From Abdalla et al., we obtain instantiations of DMCFE schemes in the standard model (from DDH, Paillier, or LWE) but without labels. From Chotard et al., we obtain a DMCFE scheme with labels still in the random oracle model, but without pairings.
2018
EUROCRYPT
2018
CRYPTO
On the Local Leakage Resilience of Linear Secret Sharing Schemes 📺
We consider the following basic question: to what extent are standard secret sharing schemes and protocols for secure multiparty computation that build on them resilient to leakage? We focus on a simple local leakage model, where the adversary can apply an arbitrary function of a bounded output length to the secret state of each party, but cannot otherwise learn joint information about the states.We show that additive secret sharing schemes and high-threshold instances of Shamir’s secret sharing scheme are secure under local leakage attacks when the underlying field is of a large prime order and the number of parties is sufficiently large. This should be contrasted with the fact that any linear secret sharing scheme over a small characteristic field is clearly insecure under local leakage attacks, regardless of the number of parties. Our results are obtained via tools from Fourier analysis and additive combinatorics.We present two types of applications of the above results and techniques. As a positive application, we show that the “GMW protocol” for honest-but-curious parties, when implemented using shared products of random field elements (so-called “Beaver Triples”), is resilient in the local leakage model for sufficiently many parties and over certain fields. This holds even when the adversary has full access to a constant fraction of the views. As a negative application, we rule out multi-party variants of the share conversion scheme used in the 2-party homomorphic secret sharing scheme of Boyle et al. (Crypto 2016).
2018
PKC
Hash Proof Systems over Lattices Revisited
Fabrice Benhamouda Olivier Blazy Léo Ducas Willy Quach
Hash Proof Systems or Smooth Projective Hash Functions (SPHFs) are a form of implicit arguments introduced by Cramer and Shoup at Eurocrypt’02. They have found many applications since then, in particular for authenticated key exchange or honest-verifier zero-knowledge proofs. While they are relatively well understood in group settings, they seem painful to construct directly in the lattice setting.Only one construction of an SPHF over lattices has been proposed in the standard model, by Katz and Vaikuntanathan at Asiacrypt’09. But this construction has an important drawback: it only works for an ad-hoc language of ciphertexts. Concretely, the corresponding decryption procedure needs to be tweaked, now requiring q many trapdoor inversion attempts, where q is the modulus of the underlying Learning With Errors (LWE) problem.Using harmonic analysis, we explain the source of this limitation, and propose a way around it. We show how to construct SPHFs for standard languages of LWE ciphertexts, and explicit our construction over a tag-IND-CCA2 encryption scheme à la Micciancio-Peikert (Eurocrypt’12). We then improve our construction and our analysis in the case where the tag is known in advance or fixed (in the latter case, the scheme is only IND-CPA) with a super-polynomial modulus, to get a stronger type of SPHF, which was never achieved before for any language over lattices.Finally, we conclude with applications of these SPHFs: password-based authenticated key exchange, honest-verifier zero-knowledge proofs, and a relaxed version of witness encryption.
2018
TCC
Two-Round Adaptively Secure Multiparty Computation from Standard Assumptions
We present the first two-round multiparty computation (MPC) protocols secure against malicious adaptive corruption in the common reference string (CRS) model, based on DDH, LWE, or QR. Prior two-round adaptively secure protocols were known only in the two-party setting against semi-honest adversaries, or in the general multiparty setting assuming the existence of indistinguishability obfuscation (iO).Our protocols are constructed in two steps. First, we construct two-round oblivious transfer (OT) protocols secure against malicious adaptive corruption in the CRS model based on DDH, LWE, or QR. We achieve this by generically transforming any two-round OT that is only secure against static corruption but has certain oblivious sampleability properties, into a two-round adaptively secure OT. Prior constructions were only secure against semi-honest adversaries or based on iO.Second, building upon recent constructions of two-round MPC from two-round OT in the weaker static corruption setting [Garg and Srinivasan, Benhamouda and Lin, Eurocrypt’18] and using equivocal garbled circuits from [Canetti, Poburinnaya and Venkitasubramaniam, STOC’17], we show how to construct two-round adaptively secure MPC from two-round adaptively secure OT and constant-round adaptively secure MPC, with respect to both malicious and semi-honest adversaries. As a corollary, we also obtain the first 2-round MPC secure against semi-honest adaptive corruption in the plain model based on augmented non-committing encryption (NCE), which can be based on a variety of assumptions, CDH, RSA, DDH, LWE, or factoring Blum integers. Finally, we mention that our OT and MPC protocols in the CRS model are, in fact, adaptively secure in the Universal Composability framework.
2017
PKC
2017
PKC
2017
CRYPTO
2017
CRYPTO
2017
JOFC
2016
EUROCRYPT
2016
PKC
2015
EPRINT
2015
EPRINT
2015
EPRINT
2015
EPRINT
2015
EPRINT
2015
PKC
2015
EUROCRYPT
2015
CRYPTO
2015
CRYPTO
2015
ASIACRYPT
2014
CRYPTO
2014
EPRINT
2014
EPRINT
2014
EPRINT
2014
EPRINT
2014
ASIACRYPT
2013
PKC
2013
PKC
2013
CRYPTO
2013
ASIACRYPT

Program Committees

Eurocrypt 2020
Crypto 2018
Eurocrypt 2017
PKC 2017