Quantum Cryptography
Quantum cryptography is one of the most promising applications of quantum information theory which is already available commercially. There are two aspects of quantum cryptography which need development. First is that in order to establish it at large distances, one has to use quantum repeaters, realization of which meets serious technical obstacles, and has not yet been achieved. Second, is that a user is not likely to trust specification of quantum-cryptographic device, which leads to novel domain – (quantum) device independent cryptography in opposed to traditional quantum cryptography which can be called device dependent. KCIK researchers have contributed to both of these two aspects.

KCIK researchers has contributed to finding that cryptographic key may not be “transitive” [1] one cannot distribute large amount of key in double distance via any repeater-like protocol using certain quantum states in spite of the fact that these states (called private states) enable point to point secure connection.

We have also introduced a semi-device independent protocol, in which only dimensionality of send signals is assumed to be known [2]. We has contributed to proving the security of such a protocol against detector blinding attacks [3]. KCIK researchers took part in development of a device independent analogue of the SARG protocol of quantum key distribution based on the Hardy’s paradox [4].

[1] S. Bäuml, M. Christandl, K. Horodecki, A. Winter, Limitations on Quantum Key Repeaters, Nature Communications 6, Article number: 6908 (2015).
[2] M. Pawlowski, N. Brunner, Semi-device-independent security of one-way quantum key distribution, Phys. Rev. A 84, 010302(R) (2011).
[3] A. Chaturvedi, M. Ray, R. Veynar, M. Pawlowski, Security of QKD protocols against detector blinding attacks, Preprint at http://arxiv.org/abs/1504.00939 (2015).
[4] R. Rahaman, M.G. Parker, P. Mironowicz, M. Pawłowski, Device-independent quantum key distribution based on measurement inputs, Journal-ref: Phys. Rev. A 92, 062304 (2015).