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Article

Cryptography with Disposable Backdoors

1
Academia Sinica, Taipei 11529, Taiwan
2
The Graduate Center, City University of New York, New York, NY 10035, USA
3
Institute of Communications Engineering, National Chiao Tung University, Hsinchu 30010, Taiwan
4
School of Informatics, University of Edinburgh, South Bridge, Edinburgh EH8 9YL, UK
*
Author to whom correspondence should be addressed.
Cryptography 2019, 3(3), 22; https://doi.org/10.3390/cryptography3030022
Received: 1 July 2019 / Revised: 30 July 2019 / Accepted: 13 August 2019 / Published: 20 August 2019
(This article belongs to the Special Issue Quantum Cryptography and Cyber Security)
Backdooring cryptographic algorithms is an indisputable taboo in the cryptographic literature for a good reason: however noble the intentions, backdoors might fall in the wrong hands, in which case security is completely compromised. Nonetheless, more and more legislative pressure is being produced to enforce the use of such backdoors. In this work we introduce the concept of disposable cryptographic backdoors which can be used only once and become useless after that. These exotic primitives are impossible in the classical digital world without stateful and secure trusted hardware support, but, as we show, are feasible assuming quantum computation and access to classical stateless hardware tokens. Concretely, we construct a disposable (single-use) version of message authentication codes, and use them to derive a black-box construction of stateful hardware tokens in the above setting with quantum computation and classical stateless hardware tokens. This can be viewed as a generic transformation from stateful to stateless tokens and enables, among other things, one-time programs and memories. This is to our knowledge the first provably secure construction of such primitives from stateless tokens. As an application of disposable cryptographic backdoors we use our constructed primitive above to propose a middle-ground solution to the recent legislative push to backdoor cryptography: the conflict between Apple and FBI. We show that it is possible for Apple to create a one-time backdoor which unlocks any single device, and not even Apple can use it to unlock more than one, i.e., the backdoor becomes useless after it is used. We further describe how to use our ideas to derive a version of CCA-secure public key encryption, which is accompanied with a disposable (i.e., single-use, as in the above scenario) backdoor. View Full-Text
Keywords: one-time backdoors; one-time memories; disposable message authentication codes one-time backdoors; one-time memories; disposable message authentication codes
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MDPI and ACS Style

Chung, K.-M.; Georgiou, M.; Lai, C.-Y.; Zikas, V. Cryptography with Disposable Backdoors. Cryptography 2019, 3, 22. https://doi.org/10.3390/cryptography3030022

AMA Style

Chung K-M, Georgiou M, Lai C-Y, Zikas V. Cryptography with Disposable Backdoors. Cryptography. 2019; 3(3):22. https://doi.org/10.3390/cryptography3030022

Chicago/Turabian Style

Chung, Kai-Min; Georgiou, Marios; Lai, Ching-Yi; Zikas, Vassilis. 2019. "Cryptography with Disposable Backdoors" Cryptography 3, no. 3: 22. https://doi.org/10.3390/cryptography3030022

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