Long-distance device-independent quantum key distribution

Besides being a beautiful idea, device-independent quantum key distribution (DIQKD) is probably the ultimate solution to defeat quantum hacking. To guarantee security, it requires, however, that the fair-sampling loophole is closed, which results in a very limited maximum achievable distance. To overcome this limitation, DIQKD must be furnished with fair-sampling devices like, for instance, qubit amplifiers. These devices can herald the arrival of a photon to the receiver and thus decouple channel loss from the selection of the measurement settings. Consequently, one can safely postselect the heralded events and discard the rest, which results in a significant enhancement of the achievable distance. In this work, we investigate photonic-based DIQKD assisted by two main types of qubit amplifiers in the finite data block size scenario, and study the resources -- particularly, the detection efficiency of the photodetectors and the quality of the entanglement sources -- that would be necessary to achieve long-distance DIQKD within a reasonable time frame of signal transmission.Comment: 37 pages, 15 figure

Quantum authentication of classical messages

Although key distribution is arguably the most studied context on which to apply quantum cryptographic techniques, message authentication, i.e., certifying the identity of the message originator and the integrity of the message sent, can also benefit from the use of quantum resources. Classically, message authentication can be performed by techniques based on hash functions. However, the security of the resulting protocols depends on the selection of appropriate hash functions, and on the use of long authentication keys. In this paper we propose a quantum authentication procedure that, making use of just one qubit as the authentication key, allows the authentication of binary classical messages in a secure manner.Comment: LaTeX, 6 page

Heralded qubit amplifiers for practical device-independent quantum key distribution

Device-independent quantum key distribution does not need a precise quantum mechanical model of employed devices to guarantee security. Despite of its beauty, it is still a very challenging experimental task. We compare a recent proposal by Gisin et al. [Phys. Rev. Lett. 105, 070501 (2010)] to close the detection loophole problem with that of a simpler quantum relay based on entanglement swapping with linear optics. Our full-mode analysis for both schemes confirms that, in contrast to recent beliefs, the second scheme can indeed provide a positive key rate which is even considerably higher than that of the first alternative. The resulting key rates and required detection efficiencies of approx. 95% for both schemes, however, strongly depend on the underlying security proof.Comment: 5 pages, 3 figure

Secure quantum key distribution with a subset of malicious devices

The malicious manipulation of quantum key distribution (QKD) hardware is a serious threat to its security, as, typically, neither end users nor QKD manufacturers can validate the integrity of every component of their QKD system in practice. One possible approach to re-establish the security of QKD is to use a redundant number of devices. Following this idea, we introduce an efficient distributed QKD post-processing protocol and prove its security in a variety of corruption models of the possibly malicious devices. We find that, compared to the most conservative model of active and collaborative corrupted devices, natural assumptions lead to a significant enhancement of the secret key rate and considerably simpler QKD setups. Furthermore, we show that, for most practical situations, the resulting finite-size secret key rate is similar to that of the standard scenario assuming trusted devices.Comment: 35 pages, 6 figure