On Pseudorandom Encodings

We initiate a systematic study of pseudorandom encodings: efficiently computable and decodable encoding functions that map messages from a given distribution to a randomlooking distribution. For instance, every distribution that can be perfectly compressed admits such a pseudorandom encoding. Pseudorandom encodings are motivated by a variety of cryptographic applications, including password-authenticated key exchange, “honey encryption” and steganography. The main question we ask is whether every efficiently samplable distribution admits a pseudorandom encoding. Under different cryptographic assumptions, we obtain positive and negative answers for different flavors of pseudorandom encodings and relate this question to problems in other areas of cryptography. In particular, by establishing a twoway relation between pseudorandom encoding schemes and efficient invertible sampling algorithms, we reveal a connection between adaptively secure multi-party computation and questions in the domain of steganography. ∗Supported by ERC Project PREP-CRYPTO 724307. †Supported by ERC Projects PREP-CRYPTO 724307 and CryptoCloud 339563. Work done in part while visiting UCLA and the Technion. ‡Supported by ERC Project NTSC (742754), NSF-BSF grant 2015782, BSF grant 2018393, and a grant from the Ministry of Science and Technology, Israel and Department of Science and Technology, Government of India. §Supported by the NSF SaTC award 1817143. ¶Supported in part by DARPA SAFEWARE and SIEVE awards, NTT Research, NSF Frontier Award 1413955, and NSF grant 1619348, BSF grant 2012378, a Xerox Faculty Research Award, a Google Faculty Research Award, an equipment grant from Intel, and an Okawa Foundation Research Grant. This material is based upon work supported by the Defense Advanced Research Projects Agency through the ARL under Contract W911NF-15C-0205. The views expressed are those of the authors and do not reflect the official policy or position of the Department of Defense, the National Science Foundation, NTT Research, or the U.S. Government.

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