International Association for Cryptologic Research

International Association
for Cryptologic Research


Computational Wiretap Coding from Indistinguishability Obfuscation

Yuval Ishai , Technion
Aayush Jain , CMU
Paul Lou , UCLA
Amit Sahai , UCLA
Mark Zhandry , NTT Research
DOI: 10.1007/978-3-031-38551-3_9 (login may be required)
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Presentation: Slides
Conference: CRYPTO 2023
Abstract: A wiretap coding scheme for a pair of noisy channels $(\chB,\chE)$ enables Alice to reliably communicate a message to Bob by sending its encoding over $\chB$, while hiding the message from an adversary Eve who obtains the same encoding over $\chE$. A necessary condition for the feasibility of writeup coding is that $\chB$ is not a {\em degradation} of $\chE$, namely Eve cannot simulate Bob’s view. While insufficient in the information-theoretic setting, a recent work of Ishai, Korb, Lou, and Sahai (Crypto 2022) showed that the non-degradation condition {\em is} sufficient in the computational setting, assuming idealized flavors of obfuscation. The question of basing a similar feasibility result on standard cryptographic assumptions was left open, even in simple special cases. In this work, we settle the question for all discrete memoryless channels where the (common) input alphabet of $\chB$ and $\chE$ is {\em binary}, and with arbitrary finite output alphabet, under the standard assumptions that indistinguishability obfuscation and injective PRGs exist. In particular, this establishes the feasibility of computational wiretap coding when $\chB$ is a binary symmetric channel with crossover probability $p$ and $\chE$ is a binary erasure channel with erasure probability $e$, where $e>2p$. On the information-theoretic side, our result builds on a new polytope characterization of channel degradation for pairs of binary-input channels, which may be of independent interest.
  title={Computational Wiretap Coding from Indistinguishability Obfuscation},
  author={Yuval Ishai and Aayush Jain and Paul Lou and Amit Sahai and Mark Zhandry},