Private approximation of NP-hard functions

Authors: Shai Halevi, Robert Krauthgamer, Eyal Kushilevitz, and Kobbi Nissim.

Reference: Proceedings of the 33rd annual symposium on Theory of computing (STOC 2001), pages 550-559. ACM, 2001.

Abstract: The notion of private approximation was introduced recently by Feigenbaum, Fong, Strauss and Wright. Informally, a private approximation of a function f is another function F that approximates f in the usual sense, but does not yield any information on x other than what can be deduced from f(x). As such, F(x) is useful for private computation of f(x) (assuming that F can be computed more efficiently than f).

In this work we examine the properties and limitations of this new notion. Specifically, we show that for many NP-hard problems, the privacy requirement precludes non-trivial approximation. This is the case even for problems that otherwise admit very good approximation (e.g., problems with PTAS). On the other hand, we show that slightly relaxing the privacy requirement, by means of leaking "just a few bits of information" about x, again permits good approximation.

Keywords: NP-hardness, Approximation, Private computation.

Availability: Paper available as Compressed PostScript (94 Kbyte).

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