Speaker
Description
The goal of quantum key distribution is to establish a secure key between two or more parties. Depending on the exact task, different protocols are available. In the context of multiple parties, for example, we can distribute a common secret key among all participating parties [1]. Another task is to anonymously distribute a key between a subset of parties [2]. Both examples require multipartite entangled states, more precisely GHZ states. It is often assumed that the distribution of the state can be manipulated by an eavesdropper. Therefore, besides distributing a key, the parties would like to ensure that they actually received the assumed states. This can be accomplished if all parties have access to some measurement devices. State certification protocols are provided for different levels of assumptions. In the scenario where the measurement devices are well characterised, the GHZ state can be verified using the protocol presented in Ref. [3]. Also for the more secure device-independent (DI) scenario, where no assumptions are made about the quantum states or the working behaviour of the devices, the state can be certified [4].
Proving that a protocol, such as state certification or key distribution, is secure is already a demanding task. Most protocols are proven to be 'standalone secure'. However, this does not imply that the protocol remains secure when used as a subroutine for more complex tasks. A protocol is 'composable secure' if it can be used securely as a building block in any application. Since proving that a protocol is composable secure is even more challenging, only a few security proofs meet this standard. We aim to prove that DI state certification of multipartite states [4] is composable secure, even in the presence of dishonest parties. I will present intermediate results in my talk.
[1] Cabello, arXiv:quant-ph/0009025 (2000)
[2] Grasselli, PRX Quantum 3, 040306 (2022)
[3] Pappa, PRL 108, 260502 (2012)
[4] Murta, PRL 131, 140201 (2023)
