Dissertation Defense - Melis Pahalı (PHDEE)

Melis Pahalı – Ph.D. Electrical and Electronics Engineering

Asst. Prof. Kadir Durak – Advisor

Date: 30.12.2022

Time: 11:00

Location: AB4 B428

“TIMING SIDE CHANNEL ISSUES AND PHOTON BUDGET OPTIMIZATION IN QKD”

Asst. Prof. Kadir Durak, Özyeğin University

Prof. H. Fatih Uğurdağ, Özyeğin University

Prof. Sadi Turgut, Middle East Technical University

Asst. Prof. Ahmed Akgiray, Özyeğin University

Prof. Özgür M. Müstecaplıoğlu, Koç University

Abstract:

Prepare-and-measure and entanglement-based quantum-key-distribution (QKD) protocols are known to be vulnerable to a side-channel attack that exploits the time difference in detectors’ responses used to obtain key bits. The recommended solution against this timing side-channel attack is to use a large time bin width instead of high-resolution timing information. A common notion is that using a large bin width reduces the resolution of detectors’ responses, hence supposedly minimizing the information leakage to an eavesdropper. We challenge this conventional wisdom and demonstrate that increasing the bin width does not monotonically reduce the mutual information between the key bits and the eavesdropper’s observation of detectors’ responses. Second, we discover another parameter and show the characteristic behavior of the mutual information with respect to it. Third, we examine the effect of full-width half maximums of the detectors’ responses on mutual information. Our findings about these three points should be found in the thesis study and should be taken into account in order to estimate leakage information to a possible eavesdropper correctly.

Additionally, there is a huge effort to improve data transfer capacity in QKD technologies to make it deployable in various size establishments and on a global scale. We propose a method to increase the raw key rate in discrete-variable entanglement-based QKD systems in which a Bell’s inequality is employed for security check. We focus on a standardized E91 QKD system. This method relies on the optimization of photon budget allocation among different types of bits generated purposely and occurred unavoidably in the QKD system. Additionally, we examine the optimized values of core variables depending on various photon budgets. Meanwhile, we remind the dependencies and limitations of the photon counting process.

Bio:

Melis Pahalı received her BSc degree in Meteorological Engineering from İstanbul Technical University in 2009 and her MSc degree in Physics Engineering from İstanbul Technical University in 2017. She worked as a Teaching Assistant at Özyeğin University between October 2018 and 2022 along with her Ph.D. education. Her research focus is on quantum key distribution systems.