Damián Pitalúa-Garcia (DAMTP, Cambridge) | Quanta Seminar

Multiphoton and side-channel attacks in mistrustful quantum cryptography, and practical quantum tokens without quantum memories and experimental tests (Quantum Cryptography) My talk will comprise two parts. In the first part I discuss multiphoton attacks in mistrustful quantum cryptography [1], where malicious Alice can send and track multiphoton pulses and thereby gain information about Bob’s measurement choices, violating the protocols’ security. A theoretical framework for analysing such multiphoton attacks is given, and known and new attacks are presented. The power of these attacks is illustrated with an experiment, and their application to earlier experimental demonstrations of mistrustful quantum cryptography is discussed. Countermeasures based on selective reporting are analysed and proved inadequate. I also discuss side-channel attacks where Alice controls further degrees of freedom or sends other physical systems. In the second part I describe quantum token schemes [2] based on Kent’s S-money [3], which do not require quantum memories and/or long-distance quantum communication and are therefore practical to implement with current technology. Security is analysed in the presence of noise, losses, and experimental imperfection. These schemes satisfy near-instant validation without cross-checking and are thus useful in setting where relativistic signalling constraints are important. It is shown that, given standard assumptions in mistrustful quantum cryptographic implementations, unforgeability and user privacy could be guaranteed with attainable refinements of our off-the-shelf setup.Finally, if time allows it, I will briefly discuss the problem of quantum position authentication. [1] M. Bozzio, A. Cavailles, E. Diamanti, A. Kent and D. Pitalúa-García, “Multi-photon and side-channel attacks in mistrustful quantum cryptography”,PRX Quantum 2, 030338 (2021). [2] A. Kent, D. Lowndes, D. Pitalúa-García and J. Rarity, “Practical quantum tokens without quantum memories and experimental tests”, npj Quantum Inf 8, 28 (2022). [3] A. Kent, “S-money: virtual tokens for a relativistic economy”, Proc. R. Soc. A 475, 20190170 (2019). Quantum Information Group Website: https://www.qi.phy.cam.ac.uk/