Cryptology ePrint Archive: Report 2020/104

On the Security Goals of White-Box Cryptography

Estuardo Alpirez Bock and Alessandro Amadori and Chris Brzuska and Wil Michiels

Abstract: We discuss existing and new security notions for white-box cryptography and comment on their suitability for Digital Rights Management and Mobile Payment Applications, the two prevalent use-cases of white-box cryptography. In particular, we put forward indistinguishability for white-box cryptography with hardware-binding (IND-WHW) as a new security notion that we deem central. We also discuss the security property of application-binding and explain the issues faced when defining it as a formal security notion. Based on our proposed notion for hardware-binding, we describe a possible white-box competition setup which assesses white-box implementations w.r.t. hardware-binding. Our proposed competition setup allows us to capture hardware-binding in a practically meaningful way.

While some symmetric encryption schemes have been proven to admit plain white-box implementations, we show that not all secure symmetric encryption schemes are white-boxeable in the plain white-box attack scenario, i.e., without hardware-binding. Thus, even strong assumptions such as indistinguishability obfuscation cannot be used to provide secure white-box implementations for arbitrary ciphers. Perhaps surprisingly, our impossibility result does not carry over to the hardware-bound scenario. In particular, Alpirez Bock, Brzuska, Fischlin, Janson and Michiels (ePrint 2019/1014) proved a rather general feasibility result in the hardware-bound model. Equally important, the apparent theoretical distinction between the plain white-box model and the hardware-bound white-box model also translates into practically reduced attack capabilities as we explain in this paper.

Category / Keywords: applications / White-box cryptography, Hardware-binding, Application-binding, Security Notions, Feasibility, AES

Original Publication (in the same form): IACR-CHES-2020

Date: received 2 Feb 2020

Contact author: estuardo alpirezbock at gmail com,chris brzuska@aalto fi

Available format(s): PDF | BibTeX Citation

Note: This paper will appear in the proceedings of TCHES Volume 2020, Issue 2. Both versions of the paper are essentially identical and differ only in their formatting.

Version: 20200204:161137 (All versions of this report)

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