Quantum Cryptography in Norway

and quantum information
research at the Department of Electronics and Telecommunications, NTNU, Trondheim

Publications

Vadim Makarov and Johannes Skaar, “Faked states attack using detector efficiency mismatch on SARG04, phase-time, DPSK, and Ekert protocols,” quant-ph/0702262.
Vadim Makarov, Andrey Anisimov, and Johannes Skaar, “Effects of detector efficiency mismatch on security of quantum cryptosystems,” Phys. Rev. A 74, 022313 (2006): PDF (360KB); preprint at quant-ph/0511032.
Vadim Makarov and Dag R. Hjelme, “Faked states attack on quantum cryptosystems,” J. Mod. Opt. 52, 691-705 (2005).
Johannes Skaar, Juan Carlos Garcia Escartin, and Harald Landro, “Quantum mechanical description of linear optics,” Am. J. Phys. 72, 1385-1391 (2004).
Vadim Makarov, Alexey Brylevski, and Dag R. Hjelme, “Real-time phase tracking in single-photon interferometers,” J. Appl. Opt. 43, 4385-4392 (2004).
Artem Vakhitov, Vadim Makarov, and Dag R. Hjelme, “Large pulse attack as a method of conventional optical eavesdropping in quantum cryptography,” J. Mod. Opt. 48, 2023-2038 (2001).

Presentations and articles

Poster “Faked states attack exploiting detector efficiency mismatch on BB84, phase-time, DPSK, and Ekert protocols” (2006).
Presentation “Attacks via optical loopholes” from a quantum information theory workshop (2004).
Lecture “Quantum cryptography” given in Fiber Components course (2003).
Artikkel “Bombesikker kryptokode” i Teknisk Ukeblad (2002).
Presentation “Quantum cryptography” from the Norwegian Cryptographic Seminar (2002).

Note: if you want to read a good popular introduction into quantum cryptography, you may check a concise introduction by Artur Ekert. Actually, the best intros that popularly explain how quantum key distribution equipment works have been published in printed journals and are not available on the internet... well, here is one on-line article with pictures.

Doctoral theses

Quantum cryptography and quantum cryptanalysis. Doktor ingeniør thesis by Vadim Makarov (2007).

Master theses

Quantum cryptography systems. Master thesis by Mikhail Chizhov (2004).
Quantum cryptography and faked states attack on systems using active basis choice. Master thesis by Bendik Vignes (2004).
Quantum key distribution: Real-time compensation of interferometer phase drift. Master thesis by Alexey Brylevski (2002).
Evaluation of security against unauthorized access for practical fiber-based quantum cryptosystems. Master thesis by Artem Vakhitov (2000).
High-speed single photon detector for quantum cryptosystems. Master thesis by Kirill Vylegjanine (2000).
Single photon detection using avalanche photodiode. Master thesis by Torbjørn Nesheim (1999).

People
	Vadim Makarov, makarov@vad1.com Adjunct Professor Dag R. Hjelme Associate Professor Astrid Dyrseth Professor Johannes Skaar [everybody’s contact info & former members]

Courses
	FE8100 Quantum computers and quantum communication

About our research

In Trondheim, we are building a quantum cryptosystem that works over optical fiber, test technologies useful for practical applications of quantum cryptography, and study practical security of today’s quantum cryptosystems.

Quantum key distribution experiment

We chose interferometric (Townsend’s) scheme and BB84 protocol for our quantum key distribution channel. The setup has been fully completed and tested in the laboratory.

We have developed and used in our setup two new techniques: Tracking a rather fast phase drift in the interferometer at the single-photon level using the data from the detector, without introducing additional components into the system and without active thermostabilization measures. This may make production of hardware like the one we’re using cheaper. Single-photon detector with afterpulse blocking — a technique that overcomes pulse rate limitation of avalanche photo diodes. It allows to run the detector at 20 MHz gating rate in our setup, and in principle at much higher gating rates than that.

We have been a bit unfortunate with the experiment that demonstrates quantum key distribution. As of today, the quantum bit error rate remains rather high (4% or more, unstable) which we suspect is due to a faulty optical component in Alice’s interferometer, and the setup has not been tested with a real transmission line. We hope to eventually resolve this problem and do a ‘proper’ quantum key distribution with up to 20 km long fiber loop.

Artem Vakhitov tunes up eavesdropper's setup

Quantum cryptanalysis

This is perhaps the most interesting part of our research. We specialize on attacks via optical loopholes in quantum key distribution schemes. Several new attacks have been studied and protection measures against them proposed: Faked states attack, in which the eavesdropper doesn’t try to reconstruct the original quantum states after intercepting them, but rather constructs light pulses that look exactly like Alice’s quantum states to Bob but cause in fact the detection results determined and known by the eavesdropper. Various imperfections in Bob’s optical scheme are utilized to construct such faked states (examples are also given in the 2004 presentation; one specific imperfection — variations in detector efficiency — is analysed in two papers: 1, 2. Large pulse attack, in which modulators in Alice’s and Bob’s setups are interrogated with external light pulses without disrupting transmission of the key. This study included an eavesdropping experiment.

A little of history: Project description (PDF, 71KB) submitted to the Norwegian Research Council in 1998. It did get accepted under the Basic Telecommunications research programme, which provided us funding until 2001. Most of the work in this project was done at the Department of Electronics and Telecommunications at NTNU in Trondheim, but Telenor R&D in Oslo also participated at the early stages.