Suchetana Goswami - Quantum Software Lab, School of Informatics, University of Edinburgh, UK

Designing safe quantum networks: A journey from quantum state discrimination to authentication

In this talk, I will present the connection between fundamental quantum state discrimination and quantum cryptography. While quantum state discrimination is a broad field of interest in the quantum information research community, it finds application in several cryptographic protocols. We use the basic properties of quantum state discrimination to build several information processing tasks and authentication protocols. In distributed set-ups, the involved parties are generally considered to be spatially separated and restricted to

perform local operation and classical communication (LOCC) on their corresponding subsystems. We design data hiding protocols based on this feature. In these protocols, the aim is to hide classical information across quantum states in such a way that it remains hidden even when it is distributed among multiple parties. Additionally, this hidden information can be revealed to the trusted parties in a resource-efficient manner when

required. The foundation of designing such protocol is established by finding suitable sets of quantum states (either in qubit or higher dimension) that are indistinguishable when the corresponding parties are restricted to perform LOCC. Next, we design entanglement-based entity authentication protocols. Authentication protocols are universal notions which involve the identification of an entity Prover by another entity (considered to be the trusted party) called the Verifier. Based on the notion of quantum unclonability, we introduce hybrid entangled physically unclonable function that is used as the underlying hardware during the protocol. We prescribe two different protocols, online and offline protocols. While the offline protocol does not require any quantum communication after the protocol starts, the online one requires sharing entanglement during the verification process. The security of the protocol is governed by the properties of local indistinguishability of quantum states. We show that our protocols are secure against adversaries equipped with unbounded quantum

computational power and also require minimal hardware assumptions.