Publications by Year: 2019

Victor Balcer and Salil Vadhan. 9/2019. “Differential Privacy on Finite Computers.” in Journal Privacy Confidentiality; also presented at 9th Innovations in Theoretical Computer Science Conference (ITCS 2018) and Theory and Practice of Differential Privacy Conference (TPDP 2017). JPC PageAbstract

We consider the problem of designing and analyzing differentially private algorithms that can be implemented on discrete models of computation in strict polynomial time, motivated by known attacks on floating point implementations of real-arithmetic differentially private algorithms (Mironov, CCS 2012) and the potential for timing attacks on expected polynomial-time algorithms. As a case study, we examine the basic problem of approximating the histogram of a categorical dataset over a possibly large data universe X. The classic Laplace Mechanism (Dwork, McSherry, Nissim, Smith, TCC 2006 and J. Privacy & Condentiality 2017) does not satisfy our requirements, as it is based on real arithmetic, and natural discrete analogues, such as the Geometric Mechanism (Ghosh, Roughgarden, Sundarajan, STOC 2009 and SICOMP 2012), take time at least linear in |X|, which can be exponential in the bit length of the input.

In this paper, we provide strict polynomial-time discrete algorithms for approximate histograms whose simultaneous accuracy (the maximum error over all bins) matches that of the Laplace Mechanism up to constant factors, while retaining the same (pure) differential privacy guarantee.  One of our algorithms produces a sparse histogram as output. Its "per-bin accuracy" (the error on individual bins) is worse than that of the Laplace Mechanism by a factor of log |X|, but we prove a lower bound showing that this is necessary for any algorithm that produces a sparse histogram.  A second algorithm avoids this lower bound, and matches the per-bin accuracy of the Laplace Mechanism, by producing a compact and eciently computable representation of a dense histogram; it is based on an (n + 1) - wise independent implementation of an appropriately clamped version of the Discrete Geometric Mechanism.


Kobbi Nissim and Uri Stemmer. 3/2019. “Concentration Bounds for High Sensitivity Functions Through Differential Privacy.” Journal of Privacy and Confidentiality, 9, 1. arXiv PageAbstract

A new line of work [6, 9, 15, 2] demonstrates how differential privacy [8] can be used as a mathematical tool for guaranteeing generalization in adaptive data analysis. Specifically, if a differentially private analysis is applied on a sample S of i.i.d. examples to select a lowsensitivity function f , then w.h.p. f (S) is close to its expectation, although f is being chosen based on the data. Very recently, Steinke and Ullman [16] observed that these generalization guarantees can be used for proving concentration bounds in the non-adaptive setting, where the low-sensitivity function is fixed beforehand. In particular, they obtain alternative proofs for classical concentration bounds for low-sensitivity functions, such as the Chernoff bound and McDiarmid’s Inequality. In this work, we set out to examine the situation for functions with high-sensitivity, for which differential privacy does not imply generalization guarantees under adaptive analysis. We show that differential privacy can be used to prove concentration bounds for such functions in the non-adaptive setting.

Aaron Fluitt, Aloni Cohen, Micah Altman, Kobbi Nissim, Salome Viljoen, and Alexandra Wood. 2019. “Data Protection's Composition Problem.” European Data Protection Law Review , 5, 3, Pp. 285-292. Publisher's Version EDPL 2019.pdf
Micah Altman, Stephen Chong, and Alexandra Wood. 2019. “Formalizing Privacy Laws for License Generation and Data Repository Decision Automation.” ArXiv. ArXiv VersionAbstract
In this paper, we summarize work-in-progress on expert system support to automate some data deposit and release decisions within a data repository, and to generate custom license agreements for those data transfers.
Our approach formalizes via a logic programming language the privacy-relevant aspects of laws, regulations, and best practices, supported by legal analysis documented in legal memoranda. This formalization enables automated reasoning about the conditions under which a repository can transfer data, through interrogation of users, and the application of formal rules to the facts obtained from users. The proposed system takes the specific conditions for a given data release and produces a custom data use agreement that accurately captures the relevant restrictions on data use. This enables appropriate decisions and accurate licenses, while removing the bottleneck of lawyer effort per data transfer. The operation of the system aims to be transparent, in the sense that administrators, lawyers, institutional review boards, and other interested parties can evaluate the legal reasoning and interpretation embodied in the formalization, and the specific rationale for a decision to accept or release a particular dataset.
ArXiv 2019 - 1910.10096.pdf
Anitha Gollamudi, Owen Arden, and Stephen Chong. 2019. “Information Flow Control for Distributed Trusted Execution Environments.” Computer Security Foundations. PDF