A semiquantum key distribution (SQKD) protocol makes it possible for a quantum party and a classical party to generate a secret shared key. However, many existing SQKD protocols are not experimentally feasible in a secure way using current technology. An experimentally feasible SQKD protocol, "classical Alice with a controllable mirror" (the "Mirror protocol"), has recently been presented and proved completely robust, but it is more complicated than other SQKD protocols. Here we prove a simpler variant of the Mirror protocol (the "simplified Mirror protocol") to be completely non-robust by presenting two possible attacks against it. Our results show that the complexity of the Mirror protocol is at least partly necessary for achieving robustness.
A semiquantum key distribution (SQKD) protocol makes it possible for a quantum party and a classical party to generate a secret shared key. However, many existing SQKD protocols are not experimentally feasible in a secure way using current technology. An experimentally feasible SQKD protocol, "classical Alice with a controllable mirror" (the "Mirror protocol"), has recently been presented and proved completely robust, but it is more complicated than other SQKD protocols. Here we prove a simpler variant of the Mirror protocol (the "simplified Mirror protocol") to be completely non-robust by presenting two possible attacks against it. Our results show that the complexity of the Mirror protocol is at least partly necessary for achieving robustness.
Quantum key distribution (QKD) protocols make it possible for two quantum parties to generate a secret shared key. Semiquantum key distribution (SQKD) protocols, such as ``QKD with classical Bob'' and ``QKD with classical Alice'' (that have both been proven robust), achieve this goal even if one of the parties is classical. However, existing SQKD protocols are not experimentally feasible with current technology. Here we suggest a protocol, ``Classical Alice with a controllable mirror,'' that can be experimentally implemented with current technology (using four-level systems instead of qubits), and we prove it to be robust.
Semiquantum key distribution (SQKD) allows two parties (Alice and Bob) to create a shared secret key, even if one of these parties (say, Alice) is classical. However, most SQKD protocols suffer from severe practical security problems when implemented using photons. The recently developed “Mirror protocol” [1] is an experimentally feasible SQKD protocol overcoming those drawbacks. The Mirror protocol was proven robust (namely, it was proven secure against a limited class of attacks including all noiseless attacks), but its security in case some noise is allowed (natural or due to eavesdropping) has not been proved yet. Here we prove security of the Mirror protocol against a wide class of quantum attacks (the “collective attacks”), and we evaluate the allowed noise threshold and the resulting key rate.
The counter-intuitive features of quantum mechanics make it possible to solve problems and perform tasks that are beyond the abilities of non-quantum (classical) computers and communication devices. The field of quantum information processing studies how we can achieve such improvements by representing information as quantum states.One of the early achievements of quantum information processing is the development of quantum key distribution (QKD). QKD protocols allow two participants (Alice and Bob) to achieve the classically-impossible task of generating a secret shared key even if their adversary is computationally unlimited.Unfortunately, the security promises of QKD are true only in theory; practical implementations of QKD deviate from the theoretical protocols, and many of these deviations give rise to practical attacks. In this research thesis, we study the security properties of various QKD protocols in many practical settings:First, we study practical security of semiquantum key distribution (SQKD) protocols, where either Alice or Bob is non-quantum (classical). Following practical security problems in previous SQKD protocols, we suggest a new SQKD protocol (the "Mirror protocol") which can be securely implemented, and we prove it robust and secure against a wide range of attacks (the "uniform collective attacks").Then, we study "composable security" of the first QKD protocol created by Bennett and Brassard (BB84). BB84 has its unconditional security proved against adversaries performing the most general attacks in a theoretical (idealized) setting; however, some security approaches do not prove "composable security", which requires the secret key to remain secret even when Alice and Bob actually use it for cryptographic purposes. We generalize an algebraic security approach for BB84, making it prove composable security of BB84 (and many variants of BB84) against the most general attacks.Finally, we analyze an important practical attack (named "Bright Illumination"), showing how it can be modeled as a theoretical "Reversed-Space" attack.Overall, all results aim to enhance our understanding on how to bridge the gap between theory and practice in various sub-fields of QKD, and they may help solve a major open problem in the field of QKD: constructing a realistic QKD implementation that can be proved truly and unconditionally secure against any possible attack.
Semiquantum key distribution (SQKD) allows two parties to share a common string when one of them is quantum and the other has rather limited quantum capability. Almost all existing SQKD protocols have been proved to be robust in theory, namely that if an eavesdropper tries to gain information, he will inevitably induce some detectable errors. However, ideal devices do not exist in reality and their imperfection may result in side-channel attacks, which can be used by an adversary to get some information on the secret key string. In this paper, we design a measurement-device-independent SQKD protocol for the first time, which can remove the threat of all detector side-channel attacks and show that it is also robust. In addition, we discuss the possible use of the proposed protocol in real-world applications and in QKD networks.
Quantum cryptography has attracted much attention in recent years. In most existing quantum cryptographic protocols, players usually need the full quantum power of generating, manipulating or measuring quantum states. Semiquantum cryptography was proposed to deal with the issue that some players require only partial quantum power, such as preparing or measuring quantum states in the classical basis, which simplifies the implementations of quantum cryptography. However, the efficiency of the existing semiquantum cryptographic protocols was relatively low from a practical point of view. In this paper, we devise some new semiquantum key distribution (SQKD) protocols which highly improve the efficiency of the most well-known SQKD protocols [Phys. Rev. Lett. 99, 140501 (2007) & Phys. Rev. A 79, 052312 (2009)]. By letting players select their actions asymmetrically, the efficiency of our new protocols can be made asymptotically close to 100%. Besides, one of our proposed protocols also utilizes the discarded X-SIFT bits in the original SQKD protocol, which further improves the efficiency of SQKD. We prove that the proposed SQKD protocols are completely robust against the most general attack.
Abstract In this paper, a novel semiquantum key distribution (SQKD) protocol is proposed by using Bell state, where quantum Alice can sharesecret bits with classical Bob via quantum channel. Classical Bob is required to measure particles with thebasis, produce fresh particles within thebasis and send particles via quantum channel. Security analysis turns out that this protocol is immune to various attacks launched by the outside eavesdropper. Compared with present SQKD protocols using Bell states without a third party, on one hand, this protocol has the highest qubit efficiency; and on the other hand, the reflecting operations of the classical user in this protocol contribute to the generation of final shared key.