Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Quantum cryptography theory has a proven security defect

07.08.2012
Researchers at Tamagawa University, Quantum ICT Research Institute, (Director: Osamu Hirota, 6-1-1 Tamagawa Gakuen, Machida, Tokyo, Japan), announced today that they had proved the incompleteness and limit of the security theory in quantum key distribution. They showed that the present theory cannot guarantee unconditional security.

Details will be described at the SPIE conference on Quantum Communication and Quantum Imaging held in San Diego on August 15, 2012.

Until now, the majority of researchers in quantum information science have believed that quantum cryptography (quantum key distribution) can provide unconditional security. The guarantee of its unconditional security is given by the trace distance, which is a quantum version of the evaluation of a mathematical cipher.

However, since 2006, new developments in the field have cast criticism over the meaningful security of cryptography ensured only by the trace distance. Despite these criticisms, many papers have continued to claim that the trace distance guarantees unconditional security in quantum key distribution.

Researchers at Quantum ICT have now succeeded in clarifying a logical path between the present theory and criticisms of it. Consequently, they have proved that the present theory does not work to quantify security, and cannot provide the unconditional security given in Shannon’s theory, the theory that rigorously defines the security for an unbreakable cipher.

The details of this work will be presented at the SPIE conference on Quantum Communication and Quantum Imaging held in San Diego on August 15, 2012.

The title of the talk is “Incompleteness and Limit of Quantum Key Distribution Theory”.

Result Summary
Many papers claim that the trace distance, d, guarantees unconditional security in quantum key distribution (QKD). In our paper, first we explain explicitly the main misconception in the claim of unconditional security for QKD theory. In general terms, the cause of the misunderstanding in the security claim is the Lemma in Renner’s paper. It suggests that the generation of a perfect random key is assured by the probability (1-d), and that its failure probability is d. Thus, it concludes that the generated key provides a perfect random key sequence when the protocol succeeds. In this way QKD provides perfect secrecy (unconditional security) to a type of encryption termed ‘the one-time pad’.
H. P. Yuen at Northwestern University proved that the trace distance quantity does not give the probability of such an event. If d is not small enough, the generated key sequence is never perfectly random. The evaluation of the trace distance now requires reconstruction if it is to be used. However, QKD theory groups have not accepted this criticism, and have invented many upper-bound evaluation theories for the trace distance.
We clarified that the most recent upper bound theories for the trace distance are constructed again by the reasoning of Renner, who originally introduced the concept. It is thus unsuitable to quantify the information theoretic security of QKD, and the unconditional security defined by Shannon is not satisfied.

Consequently, Yuen’s theory is correct, and at present there is no theoretical proof of the unconditional security for any QKD.

Background

Quantum information science holds enormous promise for entirely new kinds of computing and communications, including important problems that are intractable using conventional digital technology. The most expected field is quantum cryptography. But realizing that promise will depend on theoretical guarantee of the security and the ability to transfer an extremely fragile quantum condition. Recently it has been pointed out sometimes that, in general, scientists are not familiar with practical applications. The quantum cryptography (quantum key distribution: QKD) is a typical example of the stern realities.

Now, despite enormous progress in theoretical QKD, many theory groups are still discussing the security proof for QKD based on Renner’s trace distance theory. One of reasons is that H.P.Yuen (Northwestern University) pointed out that the present theory does not guarantee the security of the real QKD system [1,2].

Recently, Renner et al announced that in any practical implementation, the generated key length is limited by the available resources, and the present security proofs are not established rigorously in such a situation. And they published own improvement result in Nature Communication in 2012 [3]. However, without the review of the incompleteness of the theory, it is repeatedly and persistently claimed that a specific trace distance criterion would guarantee unconditional security in QKD. And, unfortunately, almost all the theory groups on QKD ignored the criticisms. This is disagreeable in the development of science and technology. Researchers are obliged to clarify "what is going on" in the discussion of the scientific theory.

At present, there is no review on such a dispute. Our purpose is to clarify a story of the argument on the recent theory of QKD and the criticism against them. We introduced the Shannon theory on the cryptography to confirm the basis of the concept of the unconditional security. And we compared the fundamental concept of the current security theory of QKD by R.Renner and. the outline of the Yuen's criticism. Finally, we provided evidence on which there is no theoretical proof of the unconditional security for any QKD, despite that many theoretical papers claimed the perfect proof of the unconditional security.

[1] H.P.Yuen, Key generation: Foundation and a new quantum approach,
IEEE J. Selected topics in Quantum Electronics, vol-15, no-6, pp1630-1645, 2009.
[2] H.P.Yuen, Fundamental quantitative security in quantum key distribution,
Physical Review A, vol-82, 062304, 2010.
[3] M.Tomamichel, C.Lim, N.Gisin, and R.Renner, Tight finite-key analysis for quantum cryptography,

Nature Communication, vol-3, p639, 2012.

Tamagawa University Contact:
Osamu Hirota
Director of Quantum ICT Research Institute, Tamagawa University
6-1-1 Tamagawa Gakuen, Machida, Tokyo, 194-8610, Japan
E-mail: hirota@lab.tamagawa.ac.jp

Osamu Hirota | Tamagawa University
Further information:
http://www.tamagawa.ac.jp

More articles from Physics and Astronomy:

nachricht Transportable laser
23.01.2018 | Physikalisch-Technische Bundesanstalt (PTB)

nachricht New for three types of extreme-energy space particles: Theory shows unified origin
23.01.2018 | Penn State

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Optical Nanoscope Allows Imaging of Quantum Dots

Physicists have developed a technique based on optical microscopy that can be used to create images of atoms on the nanoscale. In particular, the new method allows the imaging of quantum dots in a semiconductor chip. Together with colleagues from the University of Bochum, scientists from the University of Basel’s Department of Physics and the Swiss Nanoscience Institute reported the findings in the journal Nature Photonics.

Microscopes allow us to see structures that are otherwise invisible to the human eye. However, conventional optical microscopes cannot be used to image...

Im Focus: Artificial agent designs quantum experiments

On the way to an intelligent laboratory, physicists from Innsbruck and Vienna present an artificial agent that autonomously designs quantum experiments. In initial experiments, the system has independently (re)discovered experimental techniques that are nowadays standard in modern quantum optical laboratories. This shows how machines could play a more creative role in research in the future.

We carry smartphones in our pockets, the streets are dotted with semi-autonomous cars, but in the research laboratory experiments are still being designed by...

Im Focus: Scientists decipher key principle behind reaction of metalloenzymes

So-called pre-distorted states accelerate photochemical reactions too

What enables electrons to be transferred swiftly, for example during photosynthesis? An interdisciplinary team of researchers has worked out the details of how...

Im Focus: The first precise measurement of a single molecule's effective charge

For the first time, scientists have precisely measured the effective electrical charge of a single molecule in solution. This fundamental insight of an SNSF Professor could also pave the way for future medical diagnostics.

Electrical charge is one of the key properties that allows molecules to interact. Life itself depends on this phenomenon: many biological processes involve...

Im Focus: Paradigm shift in Paris: Encouraging an holistic view of laser machining

At the JEC World Composite Show in Paris in March 2018, the Fraunhofer Institute for Laser Technology ILT will be focusing on the latest trends and innovations in laser machining of composites. Among other things, researchers at the booth shared with the Aachen Center for Integrative Lightweight Production (AZL) will demonstrate how lasers can be used for joining, structuring, cutting and drilling composite materials.

No other industry has attracted as much public attention to composite materials as the automotive industry, which along with the aerospace industry is a driver...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

10th International Symposium: “Advanced Battery Power – Kraftwerk Batterie” Münster, 10-11 April 2018

08.01.2018 | Event News

See, understand and experience the work of the future

11.12.2017 | Event News

Innovative strategies to tackle parasitic worms

08.12.2017 | Event News

 
Latest News

Rutgers scientists discover 'Legos of life'

23.01.2018 | Life Sciences

Seabed mining could destroy ecosystems

23.01.2018 | Earth Sciences

Transportable laser

23.01.2018 | Physics and Astronomy

VideoLinks Science & Research
Overview of more VideoLinks >>>