International Association for Cryptologic Research

International Association
for Cryptologic Research

CryptoDB

Goichiro Hanaoka

Publications

Year
Venue
Title
2021
PKC
Impossibility on Tamper-Resilient Cryptography with Uniqueness Properties 📺
In this work, we show negative results on the tamper-resilience of a wide class of cryptographic primitives with uniqueness properties, such as unique signatures, verifiable random functions, signatures with unique keys, injective one-way functions, and encryption schemes with a property we call unique-message property. Concretely, we prove that for these primitives, it is impossible to derive their (even extremely weak) tamper-resilience from any common assumption, via black-box reductions. Our proofs exploit the simulatable attack paradigm proposed by Wichs (ITCS ’13), and the tampering model we treat is the plain model, where there is no trusted setup.
2019
PKC
Improved Security Evaluation Techniques for Imperfect Randomness from Arbitrary Distributions
Dodis and Yu (TCC 2013) studied how the security of cryptographic primitives that are secure in the “ideal” model in which the distribution of a randomness is the uniform distribution, is degraded when the ideal distribution of a randomness is switched to a “real-world” (possibly biased) distribution that has some lowerbound on its min-entropy or collision-entropy. However, in many constructions, their security is guaranteed only when a randomness is sampled from some non-uniform distribution (such as Gaussian in lattice-based cryptography), in which case we cannot directly apply the results by Dodis and Yu.In this paper, we generalize the results by Dodis and Yu using the Rényi divergence, and show how the security of a cryptographic primitive whose security is guaranteed when the ideal distribution of a randomness is a general (possibly non-uniform) distribution Q, is degraded when the distribution is switched to another (real-world) distribution R. More specifically, we derive two general inequalities regarding the Rényi divergence of R from Q and an adversary’s advantage against the security of a cryptographic primitive. As applications of our results, we show (1) an improved reduction for switching the distributions of distinguishing problems with public samplability, which is simpler and much tighter than the reduction by Bai et al. (ASIACRYPT 2015), and (2) how the differential privacy of a mechanism is degraded when its randomness comes from not an ideal distribution Q but a real-world distribution R. Finally, we show methods for approximate-sampling from an arbitrary distribution Q with some guaranteed upperbound on the Rényi divergence (of the distribution R of our sampling methods from Q).
2018
EUROCRYPT
2018
PKC
Fast Lattice Basis Reduction Suitable for Massive Parallelization and Its Application to the Shortest Vector Problem
The hardness of the shortest vector problem for lattices is a fundamental assumption underpinning the security of many lattice-based cryptosystems, and therefore, it is important to evaluate its difficulty. Here, recent advances in studying the hardness of problems in large-scale lattice computing have pointed to need to study the design and methodology for exploiting the performance of massive parallel computing environments. In this paper, we propose a lattice basis reduction algorithm suitable for massive parallelization. Our parallelization strategy is an extension of the Fukase–Kashiwabara algorithm (J. Information Processing, Vol. 23, No. 1, 2015). In our algorithm, given a lattice basis as input, variants of the lattice basis are generated, and then each process reduces its lattice basis; at this time, the processes cooperate and share auxiliary information with each other to accelerate lattice basis reduction. In addition, we propose a new strategy based on our evaluation function of a lattice basis in order to decrease the sum of squared lengths of orthogonal basis vectors. We applied our algorithm to problem instances from the SVP Challenge. We solved a 150-dimension problem instance in about 394 days by using large clusters, and we also solved problem instances of dimensions 134, 138, 140, 142, 144, 146, and 148. Since the previous world record is the problem of dimension 132, these results demonstrate the effectiveness of our proposal.
2018
ASIACRYPT
Attribute-Based Signatures for Unbounded Languages from Standard Assumptions
Attribute-based signature (ABS) schemes are advanced signature schemes that simultaneously provide fine-grained authentication while protecting privacy of the signer. Previously known expressive ABS schemes support either the class of deterministic finite automata and circuits from standard assumptions or Turing machines from the existence of indistinguishability obfuscations.In this paper, we propose the first ABS scheme for a very general policy class, all deterministic Turing machines, from a standard assumption, namely, the Symmetric External Diffie-Hellman (SXDH) assumption. We also propose the first ABS scheme that allows nondeterministic finite automata (NFA) to be used as policies. Although the expressiveness of NFAs are more restricted than Turing machines, this is the first scheme that supports nondeterministic computations as policies.Our main idea lies in abstracting ABS constructions and presenting the concept of history of computations; this allows a signer to prove possession of a policy that accepts the string associated to a message in zero-knowledge while also hiding the policy, regardless of the computational model being used. With this abstraction in hand, we are able to construct ABS for Turing machines and NFAs using a surprisingly weak NIZK proof system. Essentially we only require a NIZK proof system for proving that a (normal) signature is valid. Such a NIZK proof system together with a base signature scheme are, in turn, possible from bilinear groups under the SXDH assumption, and hence so are our ABS schemes.
2016
CRYPTO
2016
PKC
2016
PKC
2016
PKC
2016
ASIACRYPT
2016
ASIACRYPT
2015
TCC
2015
ASIACRYPT
2015
ASIACRYPT
2015
ASIACRYPT
2014
CRYPTO
2014
PKC
2014
PKC
2014
TCC
2013
PKC
2013
PKC
2012
CRYPTO
2012
PKC
2012
PKC
2012
PKC
2012
PKC
2012
PKC
2011
PKC
2011
PKC
2008
ASIACRYPT
2007
ASIACRYPT
2006
PKC
2005
ASIACRYPT
2004
PKC
2002
ASIACRYPT
2002
EUROCRYPT
2002
PKC
2001
PKC
2000
ASIACRYPT
1999
ASIACRYPT

Program Committees

Asiacrypt 2018
Eurocrypt 2016
PKC 2015
Crypto 2013
Asiacrypt 2009
PKC 2004