Myrto Arapinis

Physical Unclonable Functions (PUFs) are physical devices that have unique behaviour which is hard to clone. These hardware structures are considered as an effective and feasible security primitive. The application of a wide variety of PUF structures for different security purposes such as identification and key generation has been widely studied in the context of Classical PUFs. In addition, the quantum-readout PUF (QR-PUF) has been studied as a proposition for a quantum version of classical PUFs. In this paper, we do a comprehensive study on Quantum Physical Unclonable Functions with quantum cryptographic tools. We use a quantum game-based security framework for our analysis and we define a new class of quantum attacks, called General Quantum Emulation Attack (GQEA), applicable on current quantum-readout and hybrid quantum-classical PUFs. This class of attacks are based on using a database of inputs and outputs to emulate the action of an unknown quantum transformation on a new input. We define a concrete attack based on an existing emulation algorithm and use it to show the vulnerability of the current schemes under this attack. Furthermore, we formally define a QPUF for the first time and discuss the security of Unitary QPUFs (UQPUFs) by formally defining the unforgeability property of UQPUFs. We prove any UQPUF provides selective unforgeability property while they cannot provide unconditional and existential unforgeabilities.

We introduce a secure hardware device named a QEnclave that can secure the remote execution of quantum operations while only using classical controls. This device extends to quantum computing the classical concept of a secure enclave which isolates a computation from its environment to provide privacy and tamper-resistance. Remarkably, our QEnclave only performs single-qubit rotations, but can nevertheless be used to secure an arbitrary quantum computation even if the qubit source is controlled by an adversary. More precisely, attaching a QEnclave to a quantum computer, a remote client controlling the QEnclave can securely delegate its computation to the server solely using classical communication. We investigate the security of our QEnclave by modeling it as an ideal functionality named Remote State Rotation. We show that this resource allows blind delegated quantum computing with perfect security. Our proof relies on standard tools from delegated quantum computing. Working in the Abstract Cryptography framework, we show a construction of remote state preparation from remote state rotation preserving the security. An immediate consequence is the weakening of the requirements for blind delegated computation. While previous delegated protocols were relying on a client that can either generate or measure quantum states, we show that this same functionality can be achieved with a client that only transforms quantum states without generating or measuring them. Combined with known impossibility results for implementing remote state preparation with classical communication, our construction suggests a new way for blind secure delegated computation. Computational assumptions that circumvent this impossibility induce large overheads that prevent their practical use. But our approach does not increase the complexity of the problem, and relies on hardware assumptions that are already used in practice for classical computations. It hence provides a better way of implementing blind remote delegation on real quantum computing systems.

In this paper, we continue the line of work initiated by Boneh and Zhandry at CRYPTO 2013 and EUROCRYPT 2013 in which they formally define the notion of unforgeability against quantum adversaries. We develop a general and parameterised quantum game-based security model unifying unforgeability for both classical and quantum constructions allowing us for the first time to present a complete quantum cryptanalysis framework for unforgeability. In particular, we prove how our definitions subsume previous ones while considering more fine-grained adversarial models, capturing the full spectrum of superposition attacks. The subtlety here resides in the characterisation of a forgery. We show that the strongest level of unforgeability in our framework, namely existential unforgeability, can only be achieved if only orthogonal to previously queried messages are considered to be forgeries. We further show that deterministic constructions can only achieve the weaker notion of unforgeability, that is selective unforgeability, against such adversaries, but that selective unforgeability breaks if more general quantum adversaries (capable of general superposition attacks) are considered. On the other hand, we show that PRF is sufficient for constructing a selective unforgeable classical primitive against full quantum adversaries. Moreover, we show similar positive results relying on Pseudorandom Unitaries (PRU) for quantum primitives. \\ These results demonstrate the generality of our framework that could be applicable to other primitives beyond the cases analysed in this paper.