Sebastien Lord, University of Ottawa, Canada
Recently, there has been a growing interest in using the no-cloning principle to create uncloneable functionalities. Such an example is the notion of Secure Software Leasing (SSL) introduced by Ananth and La Placa in 2020. In an SSL scheme, a Vendor encodes a circuit $C$ as a quantum state $\rho_C$ which is then given to a User. While holding this state, the User can evaluate the circuit on any input. Furthermore, the User can return the state to the Vendor who, after successfully verifying the return, can be assured that the User no longer has the ability to evaluate the circuit $C$.
In this work, we present the first SSL scheme which is provably secure without any assumptions against unbounded adversaries. Our construction uses total authentication schemes to encode point functions. By prior work, this can then be used to construct an SSL scheme for compute-and-compare functions.
We proceed by studying quantum copy-protection, which is a notion related to SSL, but where the encoding procedure inherently prevents the splitting of a single copy of an encoding for $C$ into two parts, each allowing separate Users to evaluate $C$. We show that our construction copy-protects point functions against one honest and one malicious evaluator. We then show a generic construction of an SSL scheme from an honest-malicious copy-protection scheme.
This is joint work with Anne Broadbent, Stacey Jeffery, Supartha Podder, and Aarthi Sundaram. A manuscript is available at https://arxiv.org/abs/2101.12739.Recording of the talk