We examine security of a protocol on cryptographic key distribution viaclassical noise proposed by Yuen and Kim (Phys. Lett. A 241 135 (1998)).Theoretical and experimental analysis in terms of the secure key distributionrate shows that secure key distribution is possible even if the eavesdroppercould receive more photons than the legitimate receiver, as long as thesignal-to-noise-ratio (SNR) of the receiver is better than -9dB of theeavesdropper's SNR. Secure key distribution was demonstrated at the maximumrate of 0.04 bit per sender's bit and transmission rate of 2 Mb/s in theexperiment employing conventional fiber optics. The present protocol hasadvantages of the efficient key distribution and the simple implementation overother quantum key distribution protocols. However, careful design andmanagement are necessary to keep the security of the crypto-system.
We examine security of a protocol on cryptographic key distribution viaclassical noise proposed by Yuen and Kim (Phys. Lett. A 241 135 (1998)).Theoretical and experimental analysis in terms of the secure key distributionrate shows that secure key distribution is possible even if the eavesdroppercould receive more photons than the legitimate receiver, as long as thesignal-to-noise-ratio (SNR) of the receiver is better than -9dB of theeavesdropper's SNR. Secure key distribution was demonstrated at the maximumrate of 0.04 bit per sender's bit and transmission rate of 2 Mb/s in theexperiment employing conventional fiber optics. The present protocol hasadvantages of the efficient key distribution and the simple implementation overother quantum key distribution protocols. However, careful design andmanagement are necessary to keep the security of the crypto-system.
We examine security of a protocol on cryptographic key distribution via classical noise proposed by Yuen and Kim (Phys. Lett. A 241 135 (1998)). Theoretical and experimental analysis in terms of the secure key distribution rate shows that secure key distribution is possible even if the eavesdropper could receive more photons than the legitimate receiver, as long as the signal-to-noise-ratio (SNR) of the receiver is better than -9dB of the eavesdropper's SNR. Secure key distribution was demonstrated at the maximum rate of 0.04 bit per sender's bit and transmission rate of 2 Mb/s in the experiment employing conventional fiber optics. The present protocol has advantages of the efficient key distribution and the simple implementation over other quantum key distribution protocols. However, careful design and management are necessary to keep the security of the crypto-system.
The secure distribution of the secret random bit sequences known as `key' material, is an essential precursor to their use for the encryption and decryption of confidential communications. Quantum cryptography is an emerging technology for secure key distribution with single-photon transmissions: Heisenburg's uncertainty principle ensures that an adversary can neither successfully tap the key transmissions, nor evade detection (eavesdropping raises the key error rate above a threshold value). We have developed experimental quantum cryptography systems based on the transmission of non-orthogonal single-photon states to generate shared key material over multi-kilometer optical fiber paths and over line-of-sight links. In both cases, key material is built up using the transmission of a single- photon per bit of an initial secret random sequence. A quantum-mechanically random subset of this sequence is identified, becoming the key material after a data reconciliation stage with the sender. In our optical fiber experiment we have performed quantum key distribution over 24-km of underground optical fiber using single-photon interference states, demonstrating that secure, real-time key generation over `open' multi-km node-to-node optical fiber communications links is possible.
Abstract Cryptography is a scientific method that is used to transmit secret information. In contrast, quantum cryptography depends on physical laws to encrypt information; when the quantum computer appeared, the classic encryption method becomes inefficient. The quantum method is commonly used to distribute keys, a process called as quantum key distribution (QKD). In this paper, we consider the efficiency of the quantum method compared to classical methods. Also, we discuss the security of QKD against several attacks and provide security analysis based on probabilistic models. Additionally, the paper explains how to encrypt random numbers into a sequence of photons using a QKD system for the distribution of a key. This research demonstrates the efficiency and security of QKD in sending and distributing keys between communication parties. Thus, both the sender and the receiver would be able to obtain a security key using the quantum method rather than classical methods.
Abstract Quantum key distribution (QKD) has established itself as a groundbreaking technology, showcasing inherent security features that are fundamentally proven. Qubit-based QKD protocols that rely on binary encoding encounter an inherent constraint related to the secret key capacity. This limitation restricts the maximum secret key capacity to one bit per photon. On the other hand, qudit-based QKD protocols have their advantages in scenarios where photons are scarce and noise is present, as they enable the transmission of more than one secret bit per photon. While proof-of-principle entangled-based qudit QKD systems have been successfully demonstrated over the years, the current limitation lies in the maximum distribution distance, which remains at 20 km fiber distance. Moreover, in these entangled high-dimensional QKD systems, the witness and distribution of quantum steering have not been shown before. Here we present a high-dimensional time-bin QKD protocol based on energy-time entanglement that generates a secure finite-length key capacity of 2.39 bit/coincidences and secure cryptographic finite-length keys at 0.24 Mbits s −1 in a 50 km optical fiber link. Our system is built entirely using readily available commercial off-the-shelf components, and secured by nonlocal dispersion cancellation technique against collective Gaussian attacks. Furthermore, we set new records for witnessing both energy-time entanglement and quantum steering over different fiber distances. When operating with a quantum channel loss of 39 dB, our system retains its inherent characteristic of utilizing large-alphabet. This enables us to achieve a secure key rate of 0.30 kbits s −1 and a secure key capacity of 1.10 bit/coincidences, considering finite-key effects. Our experimental results closely match the theoretical upper bound limit of secure cryptographic keys in high-dimensional time-bin QKD protocols (Mower et al 2013 Phys. Rev. A 87 062322; Zhang et al 2014 Phys. Rev. Lett. 112 120506), and outperform recent state-of-the-art qubit-based QKD protocols in terms of secure key throughput using commercial single-photon detectors (Wengerowsky et al 2019 Proc. Natl Acad. Sci. 116 6684; Wengerowsky et al 2020 npj Quantum Inf. 6 5; Zhang et al 2014 Phys. Rev. Lett. 112 120506; Zhang et al 2019 Nat. Photon. 13 839; Liu et al 2019 Phys. Rev. Lett. 122 160501; Zhang et al 2020 Phys. Rev. Lett. 125 010502; Wei et al 2020 Phys. Rev. X 10 031030). The simple and robust entanglement-based high-dimensional time-bin protocol presented here provides potential for practical long-distance quantum steering and QKD with multiple secure bits-per-coincidence, and higher secure cryptographic keys compared to mature qubit-based QKD protocols.
Cryptography - the art of secure communications, has been developed at leastover 2500 years. Still at present, no perfectly secure as well as practicallysuitable classical or quantum cryptosystems exist. Statistically encoding theindividual bit, here we present a practical key distribution technique which isabsolutely secure both for classical and quantum keys. To achieve perfectsecurity, noise has to be strategically introduced. Noise, a detrimentalfactor, which never becomes helpful anywhere in classical and quantuminformation theory, can be used as a gift of nature in our cryptosystem sincefundamentally the coding of this cipher system does not follow the standardtechnique of classical and quantum information processing.
The quantum key distribution (QKD) system can provide the absolutely secure communication for distant users [C. H. Bennett and G. Brassard, Proc. of the IEEE Int. Conf. on Computers, Systems, and Signal Processing, pp. 175–179, 1984]. But it requires single photon sources, highly sensitive detectors, and newly constructed quantum channel between the legitimate users. On the other hand, classical (or quantum) noise based key distribution system is one of the candidates to realize the key distribution system with today’s technology [U. M. Maurer, IEEE Trans. Inform. Theory, 39, No.3, pp.733–742, 1993, H. P. Yuen and A. M. Kim, Phys. Lett. A, 241, pp.135–138, 1998]. In such a system, the independence of the noise between a legitimate receiver and an eavesdropper is presupposed. For long haul distant communication, however, amplification of the carrier is indispensable. This amplification process generates correlated fluctuations between them.We analyze how much correlation occurs when a coherent state is amplified and split. Then, the influence on the security level is shown in contrast to the non correlated case.