Beyond the Csiszár-Korner Bound: Best-Possible Wiretap Coding via Obfuscation

Beyond the Csiszár-Korner Bound: Best-Possible Wiretap Coding via Obfuscation

연구 분야: Analysis

학회: Annual International Cryptology Conference

A wiretap coding scheme (Wyner, Bell Syst. Tech. J. 1975) enables Alice to reliably communicate a message m to an honest Bob by sending an encoding c over a noisy channel , while at the same time hiding m from Eve who receives c over another noisy channel . Wiretap coding is clearly impossible when is a degraded version of , in the sense that the output of can be simulated using only the output of . A classic work of Csiszár and Korner (IEEE Trans. Inf. Theory, 1978) shows that the converse does not hold. This follows from their full characterization of the channel pairs that enable information-theoretic wiretap coding. In this work, we show that in fact the converse does hold when considering computational security; that is, wiretap coding against a computationally bounded Eve is possible if and only if is not a degraded version of . Our construction assumes the existence of virtual black-box (VBB) obfuscation of specific classes of “evasive” functions that generalize fuzzy point functions, and can be heuristically instantiated using indistinguishability obfuscation. Finally, our solution has the appealing feature of being universal in the sense that Alice’s algorithm depends only on and not on .