kvanttikryptografiassa

Kvanttikryptografia, known in Finnish as kvanttikryptografiassa, is the study and application of quantum mechanical principles to secure communication. Its foundational concept is that quantum states can be used to generate cryptographic keys that are provably secure against eavesdropping.

The most widely studied protocol is the BB84 protocol, introduced by Charles Bennett and Gilles Brassard in 1984. It uses polarized photons sent through a quantum channel; the recipients choose measurement bases at random. After transmission, they publicly compare basis choices and keep only the bits where the bases match. An eavesdropper’s measurement inevitably disturbs the quantum states, revealing their presence. Other protocols, such as B92, E91 (based on entanglement), and device-independent QKD, expand on this basic idea by using different quantum resources and security proofs that do not assume trusted devices.

Quantum key distribution (QKD) in practice requires error correction and privacy amplification to produce a secret key from the raw measurement data. Losses in optical fibers and atmospheric turbulence impose limits on distance. Ground‑based fiber links up to about 500 kilometers have been demonstrated, while satellite links have extended QKD to intercontinental scales. Projects by China, Europe, and the United States have deployed operational QKD systems, and commercial vendors provide turnkey solutions.

Security in kvanttikryptografiassa is theoretically unconditional, assuming perfect implementation. However, side channels, imperfect detectors, and device flaws can compromise security. Consequently, ongoing research focuses on tamper‑resistant hardware, measurement‑device‑independent protocols, and integration with classical post‑processing frameworks.

With the advent of quantum computers that threaten traditional public‑key schemes, kvanttikryptografiassa offers a complementary approach: it can secure keys that can later be used with classical cryptographic systems. Future developments aim to create large‑scale quantum networks, interconnect them with conventional internet infrastructure, and ensure robust defense against both classical and quantum adversaries.