Security loophole induced by photorefractive effect in continuous-variable quantum key distribution system

Area of Science:

• Quantum Information Science
• Optical Engineering
• Materials Science

Background:

• Mach-Zehnder interferometer (MZI) modulators are crucial for continuous-variable quantum key distribution (CVQKD).
• These modulators control coherent state signal intensity but are susceptible to performance degradation from non-linear effects and temperature.
• Lithium niobate (LN) crystals, commonly used in modulators, exhibit photorefractive effects (PE).

Purpose of the Study:

• To analyze the security loophole in CVQKD systems arising from the photorefractive effect in LN modulators.
• To investigate how PE-induced refractive index changes impact secret key rate estimation.
• To propose countermeasures against PE-induced security vulnerabilities in CVQKD.

Main Methods:

• Analysis of security vulnerabilities in CVQKD systems.
• Investigated the impact of photorefractive effect-induced refractive index changes in MZI modulators.
• Development and proposal of countermeasures against identified security risks.

Main Results:

• The photorefractive effect in LN modulators can cause refractive index changes.
• These changes lead to an inaccurate estimation (overestimate or underestimate) of the secret key rate in CVQKD.
• This inaccuracy creates a security loophole exploitable by eavesdroppers (Eve) using methods like intercept-resend attacks.

Conclusions:

• The photorefractive effect in LN-based CVQKD modulators presents a significant security loophole.
• Accurate estimation of secret key rates is compromised by PE-induced refractive index fluctuations.
• Proposed countermeasures effectively mitigate the identified security risks, enhancing CVQKD system security.