## Cryptology ePrint Archive: Report 2022/343

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

Yuval Ishai and Alexis Korb and Paul Lou and Amit Sahai

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 Körner (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.

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Date: received 12 Mar 2022, last revised 14 Mar 2022

Contact author: yuvali at cs technion ac il, alexiskorb at cs ucla edu, pslou at cs ucla edu, sahai at cs ucla edu

Available format(s): PDF | BibTeX Citation

Note: Changed citation for BTV12 from ePrint version to Conference Proceedings in Crypto 2012.

Short URL: ia.cr/2022/343

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