International Association for Cryptologic Research

International Association
for Cryptologic Research

CryptoDB

Lucas Kowalczyk

Affiliation: Columbia University

Publications

Year
Venue
Title
2019
EUROCRYPT
Compact Adaptively Secure ABE for $\mathsf {NC^1}$ from k-Lin
Lucas Kowalczyk Hoeteck Wee
We present compact attribute-based encryption (ABE) schemes for $$\mathsf {NC^1}$$ that are adaptively secure under the k-Lin assumption with polynomial security loss. Our KP-ABE scheme achieves ciphertext size that is linear in the attribute length and independent of the policy size even in the many-use setting, and we achieve an analogous efficiency guarantee for CP-ABE. This resolves the central open problem posed by Lewko and Waters (CRYPTO 2011). Previous adaptively secure constructions either impose an attribute “one-use restriction” (or the ciphertext size grows with the policy size), or require q-type assumptions.
2018
EUROCRYPT
2018
CRYPTO
A Simple Obfuscation Scheme for Pattern-Matching with Wildcards 📺
We give a simple and efficient method for obfuscating pattern matching with wildcards. In other words, we construct a way to check an input against a secret pattern, which is described in terms of prescribed values interspersed with unconstrained “wildcard” slots. As long as the support of the pattern is sufficiently sparse and the pattern itself is chosen from an appropriate distribution, we prove that a polynomial-time adversary cannot find a matching input, except with negligible probability. We rely upon the generic group heuristic (in a regular group, with no multilinearity). Previous work [9, 10, 32] provided less efficient constructions based on multilinear maps or LWE.
2018
CRYPTO
Hardness of Non-interactive Differential Privacy from One-Way Functions 📺
A central challenge in differential privacy is to design computationally efficient non-interactive algorithms that can answer large numbers of statistical queries on a sensitive dataset. That is, we would like to design a differentially private algorithm that takes a dataset $$D \in X^n$$D∈Xn consisting of some small number of elements n from some large data universe X, and efficiently outputs a summary that allows a user to efficiently obtain an answer to any query in some large family Q.Ignoring computational constraints, this problem can be solved even when X and Q are exponentially large and n is just a small polynomial; however, all algorithms with remotely similar guarantees run in exponential time. There have been several results showing that, under the strong assumption of indistinguishability obfuscation, no efficient differentially private algorithm exists when X and Q can be exponentially large. However, there are no strong separations between information-theoretic and computationally efficient differentially private algorithms under any standard complexity assumption.In this work we show that, if one-way functions exist, there is no general purpose differentially private algorithm that works when X and Q are exponentially large, and n is an arbitrary polynomial. In fact, we show that this result holds even if X is just subexponentially large (assuming only polynomially-hard one-way functions). This result solves an open problem posed by Vadhan in his recent survey [52].
2017
PKC
2016
TCC
2015
EPRINT
2015
CRYPTO
2015
ASIACRYPT