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Cryptography

Network-Compatible Unconditionally Secured Classical Key Distribution via Quantum Superposition-Induced Deterministic Randomness

Byoung Seung HAM

Published Jan 21, 2022• 2 citations
Publisher

Abstract

Based on the addressability of quantum superposition and its unitary transformation, a network-compatible, unconditionally secured key distribution protocol is presented for arbitrary networking in a classical regime with potential applications of one-time-pad cryptography. The network capability is due to the addressable unitary transformation between arbitrary point-to-point connections in a network through commonly shared double transmission channels. The unconditional security is due to address-sensitive eavesdropping randomness via network authentication. The proposed protocol may offer a solid platform of unconditionally secured classical cryptography for mass-data communications in a conventional network, which would be otherwise impossible.

DOI
10.3390/cryptography6010004

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Based on the addressability of quantum superposition and its unitary transformation, a network-compatible, unconditionally secured key distribution protocol is presented for arbitrary networking in a classical regime with potential applications of one-time-pad cryptography. The network capability is due to the addressable unitary transformation between arbitrary point-to-point connections in a network through commonly shared double transmission channels. The unconditional security is due to address-sensitive eavesdropping randomness via network authentication. The proposed protocol may offer a solid platform of unconditionally secured classical cryptography for mass-data communications in a conventional network, which would be otherwise impossible.
Over decades quantum cryptography has been intensively studied for unconditionally secured key distribution in a quantum regime. Due to the quantum loopholes caused by imperfect single photon detectors and/or lossy quantum channels, however, the quantum cryptography is practically inefficient and even vulnerable to eavesdropping. Here, a method of unconditionally secured key distribution potentially compatible with current fiber-optic communications networks is proposed in a classical regime for high-speed optical backbone networks. The unconditional security is due to the quantum superposition-caused measurement indistinguishability between paired transmission channels and its unitary transformation resulting in deterministic randomness corresponding to the no-cloning theorem in a quantum key distribution protocol.
Based on the detection loophole-free photon key distribution (PKD) compatible with classical optical systems, an optical key distribution (OKD) protocol is presented for unconditionally secured cryptography in fiber-optic communications networks using addressable continuous phase basis, where each communication channel is composed of paired transmission lines. The unconditional security in OKD lies in quantum superposition between the paired lines of each channel. The continuous phase basis in OKD can be applied for one-time-pad optical cryptography in networks, whose network address capacity is dependent upon the robustness of OKD to channel noises.
So far, unconditional security in key distribution processes has been confined to quantum key distribution (QKD) protocols based on the no-cloning theorem of nonorthogonal bases. Recently, a completely different approach, the unconditionally secured classical key distribution (USCKD), has been proposed for unconditional security in the purely classical regime. Unlike QKD, both classical channels and orthogonal bases are key ingredients in USCKD, where unconditional security is provided by deterministic randomness via path superposition-based reversible unitary transformations in a coupled Mach-Zehnder interferometer. Here, the first experimental demonstration of the USCKD protocol is presented.
Unconditionally secure physical key distribution schemes are very slow, and it is practically impossible to use a one-time-pad based cipher to guarantee unconditional security for the encryption of data because using the key bits more than once gives out statistical information, for example via the known-plain-text-attack or by utilizing known components of the protocol and language statistics. Here, we outline a protocol that reduces this speed problem and allows almost-one-time-pad based communication with an unconditionally secure physical key of finite length. The physical, unconditionally secure key is not used for data encryption but is employed in order to generate and share a new software-based key without any known-plain-text component. The software-only-based key distribution is then changed from computationally secure to unconditionally secure, because the communicated key-exchange data (algorithm parameters, one-way functions of random numbers, etc.) are encrypted in an unconditionally secure way with a one-time-pad. For practical applications, this combined physical/software key distribution based communication looks favorable compared to the software-only and physical-only key distribution based communication whenever the speed of the physical key distribution is much lower than that of the software-based key distribution. A mathematical security proof of this new scheme remains an open problem.
The unconditionally secured classical key distribution (USCKD) has been presented for an air turbulent free-space optical link. Even in the noisy air channels, the USCKD has shown nearly unconditionally secure communications in data transmission owing to double unitary transformation in a round-trip scheme, where the absolute phase noises in both air channels are replaced by a relative phase noise between them. Unlike classical cryptography, USCKD is based on basis randomness and thus resistant to the attack of quantum computers. Unlike quantum key distributions, USCKD is free from nonclassical light requirement such as a single photon, which is sensitive to quantum loopholes of channel loss and imperfect detectors.
The object of this research is the security of communication networks, particularly in decentralized, multi-user environments where robust data protection and integrity are critical. The issue under discussion is the rising vulnerability of conventional cryptography systems resulting from ever complex cyberattacks and the expected risks presented by quantum computing possibilities. The development of a QKD protocol employing quantum superposition to improve data security and resilience against both present and future quantum-based cyber-attacks is demonstrated by the achieved results of this work. Achieving scalability and autonomous eavesdropping detection, this protocol lets several communication nodes securely exchange randomly produced keys without centralized management. A quick analysis of the results reveals that main elements influencing the great durability, security, and adaptability of the protocol are quantum superposition and its distributed character. Without centralized authority, the characteristics of the obtained results – especially the use of optical components, detectors, and quantum sources in conjunction with classical communication channels – solve the problem of ensuring data confidentiality and integrity in a multi-user environment. This protocol's practical reach covers safe communication applications in both public and private sectors, therefore addressing situations calling for strong data protection against modern cyberattacks. Conditions for practical application include settings like government, financial, or health-related interactions when safe information flow is crucial. This QKD system offers a future-ready security solution for high-stakes environments and represents notable advancement toward protecting data from quantum and conventional attacks