Abstract: While classical encryption algorithms like RSA and ECC are based on mathematical complexity and are susceptible to attacks by quantum computers in the future, Quantum Key Distribution offers an information-theoretically secure protocol based on the laws of quantum physics. From its conception to today, Quantum Key Distribution technology has developed from a mere theory to practical implementations of quantum communication systems that implement Quantum Key Distribution through quantum states of photons.

This paper provides an overview of the existing Quantum Key Distribution technology, paying particular attention to the hardware aspects of these systems, including their building blocks, like photon sources, modulators, quantum channels, and single-photon detectors, along with implementation issues, including loss, noise, scalability, and overall complexity. Emphasis is paid to recent developments in integrated photonics and photonic integrated circuits.

In addition to conventional Quantum Key Distribution systems, this paper covers advanced Quantum Key Distribution protocols, such as Continuous-Variable Quantum Key Distribution, Measurement-Device-Independent Quantum Key Distribution and Twin-Field Quantum Key Distribution, as well as the related security threats, including side-channel and detector-related attacks. Moreover, this paper looks at how Quantum Key Distribution is evolving to quantum networks and how it can be integrated with post-quantum cryptography.

Finally, this paper addresses some of the emerging topics, including quantum internet and intelligent optimization of Quantum Key Distribution systems.

Keywords: Quantum Key Distribution, Quantum Cryptography, Measurement-Device-Independent Quantum Key Distribution, Twin-Field Quantum Key Distribution.

Downloads: | DOI: 10.17148/IJIREEICE.2026.14517