Information theory is overwhelmed by Quantum Logic; a logic that is difficult to apprehend because its counter intuitive notions seem to be opposite to our apparent world.
This Quantum Logic offers a strong contribution to IT Security, but reveals itself to be a double-edged tool: indeed, it calls into question classical cryptography, making vulnerable our encrypted data, while proposing a new data protection supposed to be perennial.
Its characteristics bring several technological breakthroughs: Quantum Computing, Quantum Cryptography and of course Quantum Communication Networks. We will try to develop further on both the implications and the limits of these applications.
Quantum Logic Characteristics
Quantum computing relies mostly on two properties: Quantum superposition and Quantum entanglement.
Quantum superposition means that a qubit, quantum equivalent to a bit, may simultaneously have a value of 0 and 1.
Quantum Entanglement implies that if we consider two entangled quantum particle, any action that fixes the state of one particle leads to the instantaneous determination of the state of the other particle, however distant they are from one another. This principle is essential for Quantum communication.
Another principle inescapable to anyone wishing to tackle Quantum computing: Quantum decoherence. A Quantum bit may never be copied, because its sole measurement brings its “destruction”: it looses its quantum characteristics to become a simple bit. Such is the effect of quantum decoherence.
This loss of coherence is due to the interaction of the quantum particle with its environment. The measurement of this particle constitutes precisely an interaction that provokes quantum decoherence: quantum superposition of states disappears and results in only one state, here either a 0 or a 1.
We are interested by quantum coherence time, which corresponds to the duration for which quantum state superposition is maintained by the qubit. This is the most difficult challenge that scientists must face in order to tackle Quantum computing and long distance Quantum communication.
Quantum Computing: first and foremost a weapon
Solutions brought by classical cryptography, which is currently employed to secure Internet communication, transactions included, relies on algorithms which implies factorization operations to crack, a task for which standard computers are inefficient.
In communication security, the current paradigm is about regular increases of asymmetrical encryption keys’ size, in order to stay ahead of current computing ability to break them. This system is therefore limited when it comes to protect information for a long duration.
Quantum computing does away with this kind of cryptography and operates a first paradigm shift: prime number factorization may now happen within polynomial time. Indeed, quantum computing needs only a fraction of the number of operations previously required to achieve a solution, therefore rendering obsolete asymmetric cryptography. For most scientists, quantum computing is no longer an issue of fundamental research, but one of R&D.
This change significantly impacts the securitization of long life data, which must be thought right away.
Quantum cryptography constitutes a return to symmetric cryptography: a sole encryption key allows the encryption and decryption of data. And in order to validate a protocol based on a symmetric encryption key, one must demonstrate that the exchange of key may be done in absolute secrecy.
This assurance is given by the laws of quantum physics itself, from the moment of creation of the key to its transportation and reception. To transmit information through quantum particles, usually a photon, is the warranty to be able to detect any spying attempt. Such an attempt would provoke errors within the data, thanks to quantum decoherence.
Quantum communication is used to transmit the encryption key, never to transmit the message itself. If no spying attempt has been made, which we may theoretically be certain, then the key may be used to encrypt the message which will then be sent on a traditional canal.
First envisaged applications and quantum computing race
Quantum computing is already a reality. Quantum devices capable of generating truly random keys, as well as quantum communication networks are commercially available. Indeed, fundamental research has advanced to the point that numerous small companies, usually rather small, are specialized in the design and distribution of such devices.
State and banking networks are the first targets of companies selling these solutions, which may use optical fiber networks already made for the Internet; however this requires the establishment of quantum repeaters that take part in quantum teleportation to cover long distances. These include for example the project of quantum communication network from Beijing to Shanghai extending over almost 2,000 km, which should be finalized in 2016. China would also have the ability to conduct the launch of a satellite equipped with a quantum communication system, for which it will be a precursor.
On quantum computing, IT giants have already invested significantly. IBM, which has been working on the subject for 30 years, was also the first company to present a quantum computer, in 1998. The computer was then constituted by two qubits. Founded in 1999, the American company D-Wave Systems is specialized in the construction of quantum computers. Today a partner of Google, it has launched this year the D-Wave-2X, supposed to host more than 1000 qubits. Yet many researchers doubt the reality of D-Wave Systems exploits. The reason for this: the company never provided any definitive proof, for reasons of protection of manufacturing secrets. Unless their teams have managed to solve one of the fundamental problems of this discipline, i.e. decoherence, it could be that this is merely a marketing operation, and that this computer has more to do with quantum simulation. This has not prevented the company to sell to Lockheed Martin a calculator comprised of 128 qubits in May 2011, or to equip in May 2013 the laboratory launched by Google in partnership with NASA and USRA, the Quantum Artificial Intelligence Lab. Its purpose is to advance research in quantum computing, particularly in regard to Machine Learning.
Indeed, if those companies are so interested in quantum computing, this is not solely for cryptography. Quantum logic allows in fact solving certain types of issues that are burdensome with traditional computing: Data mining, Machine Learning and other optimization problems in which quantum algorithm shine. Those subjects are among the core business of those companies.
Offensive capabilities are not put aside by everyone. Quantum computing strongly attracts intelligence agencies.
It is therefore no surprise that the NSA a massively invested in a project called “Penetrating Hard Targets”. Its purpose is to build a quantum computer able to break every kind of public keys, including RSA, which is used to secure websites and encrypted email communication.
Yet it is not certain that the collapse of asymmetric encryption will occur in the near future. For Seth Lloyd, a researcher at MIT and first to have proposed a technologically viable architecture to build quantum computers, a quantum computer must gather ten thousands of qubit to be able to achieve the breaking of encryption keys used today. And this is no small matter: the more qubits there are, the more the risk of interaction with the environment and self-interference increases, causing them to become decoherent.
Furthermore, the quantum computer is not intended to replace current computers, because it brings no performance gain for most uses. It is however very possible that our computers will be equipped with modules for secure exchanges by the quantum way.
A paradigm shift
The advent of quantum computing is a complete paradigm shift, because it changes the rules of defensive and offensive techniques. All data accessible on the Internet today, and which is believed to be protected by their encryption, could be laid bare, quantum computers posing as an absolute “locksmith”. In contrast, quantum communication also provides absolute security.
Obviously it concerns above all the States and large companies, including banks, since the applications imagined today are tailored for strategic sectors.
Only later quantum devices will reach the general public. Therefore, one should not expect an abrupt change in the way our computers operate in the near future.
No doubt this race in quantum offensive and defensive capabilities will be a major challenge for the next cyber war.
 Information theory, or quantum information, is a development of Shannon’s information theory that exploits the properties of quantum mechanics. The measure unit used to quantify information is the qubit.
Annex 1 : Fundamental principles of quantum physics
Quantum physics, which study has started at the end of the 19th century, aims to describe the fundamental principles operating within physical systems, especially at atomic and subatomic levels. Quantum is the minimum amount of any physical entity involved in an interaction, meaning it is an indivisible quantity of energy, movement quantity or mass. It relies mostly on:
- Wave-particle duality: Each physical object may feature properties of wave or of particle, depending on the experimental protocol used ;
- Quantum superposition:A particle may be in several different states simultaneously;
- Quantum entanglement and its corollary, Quantum nonlocality: The state of two entangled quantum particles must be described globally. Provoking a change of state of one particle induces a change of the other particle, however distant the two particles are. This is formally opposed to the local realism principle of Einstein;
- The uncertainty principle: It is impossible to know simultaneously both the location and the speed of a particle, at most may the statistical distribution of those values.
The double-slit experiment of Thomas Young had originally proved that light is a wave phenomenon. A light is placed in front of a plate pierced by two slits that allow light to pass through to the screen placed behind it. The interference pattern of the resulting image then showed light to be a wave phenomenon. This is due to the light beams passing through each slit to interfere with one another.
Later on, technological breakthroughs allowed a refinement of this experiment. By emitting light one photon at a time, we slowly begin to observe the same phenomenon: the screen is being filled one point at a time, drawing the same image that was previously observed. Though one might have initially thought that those interferences would have disappeared once photons are sent one at a time, we do see that the particle is actually interfering with itself. This confirms that the particle is present at every place it might be, as long as it is not directly observed.
Experimenting with other particles, such as electrons, shows that all particles are subject to this duality.
Annex 2 : Quantum intrication, quantum superposition and nonlocality principle
Techniques de l’Ingénieur, july 2015, L’ordinateur quantique est-il l’avenir de l’informatique ?
SAMINADAVAYR, Laurent. « Qu’est-ce qu’un ordinateur quantique et quelles possibilités laisse-t-il entrevoir ? », http://www.techniques-ingenieur.fr/actualite/articles/interview-quest-ce-quun-ordinateur-quantique-et-quelles-possibilites-laisse-t-il-entrevoir-1715/
TREGOUET, René. « L’Aventure quantique », RTFLASH, http://www.rtflash.fr/l-aventure-quantique/article
CARIOU, Gautier. « Rêve et réalité de l’ordinateur Quantique », in La Recherche N°501-502. July-august 2015, p.61.
ALLEAUME, Romain. MARKHAM, Damian. « Cryptographie : la confiance retrouvée », dans La Recherche N°501-502. July-august 2015, p.42-44.