International Association for Cryptologic Research

International Association
for Cryptologic Research


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

Alexis Korb , UCLA, Los Angeles, USA
Yuval Ishai , Technion, Haifa, Israel
Paul Lou , UCLA, Los Angeles, USA
Amit Sahai , UCLA, Los Angeles, USA
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Presentation: Slides
Conference: CRYPTO 2022
Abstract: 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 ChB while at the same time hiding m from Eve who receives c over another noisy channel ChE. Wiretap coding is clearly impossible when ChB is a degraded version of ChE, in the sense that the output of ChB can be simulated using only the output of ChE. 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 (ChB, ChE) 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 ChB is not a degraded version of ChE. 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 ChB and not on ChE.
Video from CRYPTO 2022
  title={Beyond the Csiszár-Korner Bound: Best-Possible Wiretap Coding via Obfuscation},
  author={Alexis Korb and Yuval Ishai and Paul Lou and Amit Sahai},