Prabhanjan Ananth: Secure Software Leasing

Friday, March 26, 2021 - 1:00pm to 2:30pm
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Prabhanjan Ananth
Abstract: Formulating cryptographic definitions to protect against software piracy is an important research direction that has not received much attention. Since natural definitions using classical cryptography are impossible to achieve (as classical programs can always be copied), this directs us towards using techniques from quantum computing. The seminal work of Aaronson [CCC'09] introduced the notion of quantum copy-protection precisely to address the problem of software anti-piracy. However, despite being one of the most important problems in quantum cryptography, prior to our work, there were no known provably secure solutions of quantum copy-protection for any class of functions.

We formulate an alternative definition for tackling software piracy, called secure software leasing (SSL). While weaker than quantum copy-protection, SSL is still meaningful and has interesting applications in software anti-piracy.
We present a construction of SSL for a subclass of evasive circuits (that includes natural implementations of point functions, conjunctions with wild cards, and affine testers) based on concrete cryptographic assumptions. Our construction is the first provably secure solution, based on concrete cryptographic assumptions, for software anti-piracy. To complement our positive result, we show, based on cryptographic assumptions, that there is a class of quantum unlearnable functions for which SSL does not exist. In particular, our impossibility result also rules out quantum copy-protection for an arbitrary class of quantum unlearnable functions; resolving an important open problem on the possibility of constructing copy-protection for arbitrary quantum unlearnable functions. 
Joint work with Rolando L. La Placa (MIT).