Cryptology ePrint Archive: Report 2018/957

Non-malleable Digital Lockers

Peter Fenteany and Benjamin Fuller

Abstract: An obfuscated program reveals nothing about its design other than its input/output behavior. A digital locker is an obfuscated program that outputs a stored cryptographic key if and only if a user enters a previously stored password. A digital locker is private if it provides an adversary with no information with high probability. An ideal digital locker would also prevent an adversary from mauling an obfuscation on one password and key into a new program that obfuscates a related password or key. There are no known constructions of non-malleable digital lockers (in the standard model).

Komargodski and Yogev (Eurocrypt, 2018) constructed a simpler primitive: a non-malleable keyless digital locker. For this functionality, a user can only confirm if their point is correct. This primitive is known as non-malleable point obfuscation. Their construction prevents an adversary from transforming an obfuscation into an obfuscation on a related password.

This work proposes two new composable and nonmalleable digital lockers for short keys, one for a single bit key and a second for a logarithmic length keys. Using these construction we construct the first two non-malleable digital lockers. Our full design combines a digital locker for short keys, non-malleable codes, and universal hashing. Our constructions require a common reference string.

Category / Keywords: secret-key cryptography / Digital Lockers; Point obfuscation; Virtual black-box obfuscation; Non-malleable codes

Date: received 8 Oct 2018, last revised 9 Oct 2018

Contact author: benjamin fuller at uconn edu

Available format(s): PDF | BibTeX Citation

Note: In submission

Version: 20181009:165817 (All versions of this report)

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