Quantum key distribution (QKD) is intended to produce cryptographic secret keys between two remote parties, usually called Alice and Bob. Even though QKD has been proven to be unconditionally secure against the eavesdropper, commonly called Eve, practical implementations of QKD may contain vulnerabilities that may lead to the generated secret keys being compromised. In order to detect the presence of the eavesdropper in the channel, in our proposal Alice introduces an interleaved sequence of decoy states which produce a characteristic distribution at Bob's station. Thus, in analyzing such distribution in presence and absence of the eavesdropper Eve, her activity in the channel is detected. This protocol doesn’t require changes at the quantum physical level, but it can be incorporated at the high software level.
Quantum key distribution (QKD) is intended to produce cryptographic secret keys between two remote parties, usually called Alice and Bob. Even though QKD has been proven to be unconditionally secure against the eavesdropper, commonly called Eve, practical implementations of QKD may contain vulnerabilities that may lead to the generated secret keys being compromised. In order to detect the presence of the eavesdropper in the channel, in our proposal Alice introduces an interleaved sequence of decoy states which produce a characteristic distribution at Bob's station. Thus, in analyzing such distribution in presence and absence of the eavesdropper Eve, her activity in the channel is detected. This protocol doesn’t require changes at the quantum physical level, but it can be incorporated at the high software level.
Quantum Key Distribution (QKD) is an innovative technology which exploits the laws of quantum physics to generate and distribute shared secret key for use in cryptographic devices. Quantum Key Distribution offers the advantage of ‘unconditionally secure’ key generation with the unique ability to detect eavesdropping on the key distribution channel and shows promise for high-security applications such as those found in banking, government, and military environments. However, Quantum Key Distribution is a nascent technology where realized systems suffer from implementation non-idealities, which may significantly impact system performance and security. In this article, we discuss the modeling of a decoy state enabled Quantum Key Distribution system built to study the impact of these practical limitations. Specifically, we present a thorough background on the decoy state protocol, detailed discussion of the modeled decoy state enabled Quantum Key Distribution system, and evidence for component and sub-system verification, as well as, multiple examples of system-level validation. Additionally, we bring attention to practical considerations associated with implementing the decoy state protocol security condition gained from these research activities.
Employing the fundamental laws of quantum physics, Quantum Key Distribution (QKD) promises the unconditionally secure distribution of cryptographic keys. However, in practical realisations, a QKD protocol is only secure, when the quantum bit error rate introduced by an eavesdropper unavoidably exceeds the system error rate. This condition guarantees that an eavesdropper cannot disguise his presence by simply replacing the original transmission line with a less faulty one. Unfortunately, this condition also limits the possible distance between the communicating parties, Alice and Bob, to a few hundred kilometers. To overcome this problem, we design a QKD protocol which allows Alice and Bob to distinguish system errors from eavesdropping errors. If they are able to identify the origin of their errors, they can detect eavesdropping even when the system error rate exceeds the eavesdropping error rate. To achieve this, the proposed protocol employs an alternative encoding of information in two-dimensional photon states. Errors manifest themselves as quantum bit and as index transmission errors with a distinct correlation between them in case of intercept-resend eavesdropping. As a result, Alice and Bob can tolerate lower eavesdropping and higher system error rates without compromising their privacy.
Abstract Secure communication protocols are becoming increasingly important, e.g. for internet-based communication. Quantum key distribution (QKD) allows two parties, commonly called Alice and Bob, to generate a secret sequence of 0s and 1s called a key that is only known to themselves. Classically, Alice and Bob could never be certain that their communication was not compromised by a malicious eavesdropper. Quantum mechanics however makes secure communication possible. The fundamental principle of quantum mechanics that taking a measurement perturbs the system (unless the measurement is compatible with the quantum state) also applies to an eavesdropper. Using appropriate protocols to create the key, Alice and Bob can detect the presence of an eavesdropper by errors in their measurements. As part of the QuVis Quantum Mechanics Visualisation Project, we have developed a suite of four interactive simulations that demonstrate the basic principles of three different QKD protocols. The simulations use either polarised photons or spin 1/2 particles as physical realisations. The simulations and accompanying activities are freely available for use online or download, and run on a wide range of devices including tablets and PCs. Evaluation with students over three years was used to refine the simulations and activities. Preliminary studies show that the refined simulations and activities help students learn the basic principles of QKD at both the introductory and advanced undergraduate levels.
Despite the unconditionally secure theory of quantum key distribution (QKD), several attacks have been successfully implemented against commercial QKD systems. Those systems have exhibited some flaws, as the secret key rate of corresponding protocols remains unaltered, while the eavesdropper obtains the entire secret key. We propose a new theoretical approach called quantum flows to be able to detect the eavesdropping activity in the channel without requiring additional optical components different from the BB84 protocol because the system can be implemented as a high software module. In this approach, the transmitter interleaves pairs of quantum states, referred to here as parallel and orthogonal (non-orthogonal) states, while the receiver uses active basis selection.
Quantum key distribution allows two parties, traditionally known as Alice and Bob, to establish a secure random cryptographic key if, firstly, they have access to a quantum communication channel, and secondly, they can exchange classical public messages which can be monitored but not altered by an eavesdropper, Eve. Quantum key distribution provides perfect security because, unlike its classical counterpart, it relies on the laws of physics rather than on ensuring that successful eavesdropping would require excessive computational effort. However, security proofs of quantum key distribution are not trivial and are usually restricted in their applicability to specific protocols. In contrast, we present a general and conceptually simple proof which can be applied to a number of different protocols. It relies on the fact that a cryptographic procedure called privacy amplification is equally secure when an adversary's memory for data storage is quantum rather than classical.
It seems that quantum key distribution (QKD) may be completely insecure when the message sender Alice always encodes her key bits in a fixed basis. In this paper, we present a QKD protocol with classical Alice, i.e. Alice always encodes her key bit in the {|0〉,|1〉} basis (we call it classical {0,1} basis) and the eavesdropper Eve knows this fact. We prove that our protocol is completely robust against any eavesdropping attack and present the amount of tolerable noise against Eve's individual attack. Next, we present a QKD protocol to demonstrate that secure key bits can be distributed even if neither Alice nor Bob has quantum capacities, and extend this idea to a QKD network protocol with numerous parties who have only classical capacities. Finally, we discuss that quantum is necessary in QKD for security reasons, but both Alice and Bob may be classical.