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Postdoc - Constructions, Security and Impossibilities in Quantum Cryptography -F / H- over 12 months


Your role is to work on the construction, security and impossibility results in quantum cryptography.
It is now well known that the advent of quantum computers would break all of the public key cryptography mechanisms deployed today in our mobile phones, bank cards or Internet browsers. Even if there is not yet a consensus that this “catastrophe” will happen, the risk is there, and significantly important that it is necessary to work on. In this context, several solutions exist, and a recent call for proposals from NIST will allow, in the coming years, to better study these alternatives and define new standards.
But we also know that quantum physics can also bring new approaches to cryptography. In fact, in the 1980s, researchers showed that it was theoretically possible to carry out a perfectly secure cryptographic key exchange (QKD). The idea is that the presence of an eavesdropper listening to the communications creates disturbances which can be recognized by the legitimate participants of the communication protocol. From a security point of view, this exchange of a “quantum key” is ideal in the sense that:
– the key is generated in a pure randomly way;
– even with an unlimited computing capacity, an attacker cannot obtain any information on the key that is finally exchanged.
This provides long-term security, unlike most cryptographic mechanisms deployed today. However, there are still many open problems in order to put such a system into practice, such as the financial cost of the equipment allowing such an exchange, or even the limitation of the possible distances between the two interlocutors, requiring the use of some repeaters which deteriorate the security of the communication, which is no longer unconditional. Besides, the only thing that we are really capable of doing within the so-called “quantum cryptography” is such key exchange. Once shared, it is then necessary to use conventional cryptographic systems, which are not always perfectly secure.
From a cryptographic point of view, there is still plenty of work to be carried out in this area. On the security proof aspects, there are still gaps regarding the identification, unification, advancement and application of assumptions and security proofs, in order to ensure the theoretical security of the implemented QKD protocol.
Moreover, the key exchange requires an authenticated channel, and once the key has been exchanged, it must be used to ensure the confidentiality and/or integrity of the exchanged data. The choice made on these cryptographic mechanisms should not deteriorate the ideal security that QKD brings.
It is also important to see the possibilities and limitations of quantum cryptography, by looking at mechanisms that can bring other properties, different from key exchange. Some constructions exist such as Merkle systems, position-based cryptography, oblivious transfer or secure two-party computation, but these still have many problems. In addition, certain impossibility results have shown that quantum cryptography cannot be a universal solution, and should be used with classical solutions to as to give the right cryptographic properties.
The objective of the post doc will be to study all these issues in order to fully understand what is possible or not using quantum cryptography, from both a theoretical and a practical point of view.

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42 rue des Coutures,
14000 Caen, France

Published on May 08, 2020

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