Quantum Cryptography Lecture

Centre for Quantum Information and Quantum Computing
                   Indian Institute of Science
                           Bangalore


Announces its lecture

By

Dr. Prabha Mandayam
Institute for Quantum Information
California Institute of Technology, Pasadena, USA

Title:
" Uncertainty and Complementarity in Quantum Cryptography: Security in the Noisy Storage model"

       On Wednesday the 8th  December, 2010 at 4.00 pm

Venue: Lecture Hall - I, Department of Physics, Indian Institute of Science.

Abstract

Historically, uncertainty relations have played an important role in our understanding of quantum mechanics. Recently, entropic uncertainty relations have gained prominence in the field of quantum information. In particular, they play a crucial role in analyzing the security of quantum cryptographic protocols such as quantum key-distribution and information locking. While optimal entropic uncertainty relations have been obtained for two measurements, not much is known in a general setting with more than two outcomes. We outline a novel construction of symmetric mutually unbiased bases (MUBs), using the 2n generators of the Clifford algebra in dimension d = 2^n.  These bases satisfy the symmetry property that they are cyclically permuted under a unitary transformation. We prove a lower bound for entropic uncertainty relations for any set of MUBs and show that symmetry plays a central role in obtaining tight bounds. Finally, we describe a two-party protocol based on recent cryptographic models  -- the "bounded-storage model" and  the "noisy-storage model" -- whose security is directly related to a lower bound on the average entropy of complementary bases. While the security of most cryptographic systems in use today is based on the premise that certain computational problems are hard to solve for the adversary, these models are based on the physical assumption that no large-scale reliable quantum storage is available to the cheating party. Our protocol achieves security in the bounded-storage model even if the cheating party can store all but a constant fraction of the transmitted information, thus resolving an open question on the achievable physical limits of this model. In the general setting of the noisy-storage model, our protocol extends the range of storage devices for which security can be achieved.

All are Welcome