Quantum Key Distribution: Vulnerabilities and Solutions

In quantum technology, a technique called quantum key distribution (QKD) allows two users to safely exchange encryption keys. But for the process to take place it requires fully quantum devices, which are not currently widely available. To ensure efficiency and feasibility of the process, we can implement semi-quantum key distribution (SQKD). It is a technique that combines traditional and quantum resources. However, SQKD comes with notable flaws.

The Key Vulnerability of Semi-Quantum Key Distribution (SQKD)

In quantum cryptography information is encoded in qubits. They are carried by single photons. Hence, weak lasers pose a significant security threat. This vulnerability arises due to the photon-number-splitting (PNS) attack. Here’s an example

  • Imperfect photon emitting sources: Real-world lasers are most likely to produce multiple photon pulses with varying probabilities. Since single photon lasers are not possible with real-world lasers, eavesdropping attackers can stop this chance.
  • Attacking strategy: Using advanced technology, the attackers intercept the signal and divide multi-photon pulses. Their method separates one photon, which contains a portion of the encoded data, while sending the other photons to the authorized recipient.
  • Information leakage: By measuring the stolen photon, attackers can ascertain a part of the key. They can continue this process for many pulses, gathering enough information to break the encryption.

Available Solutions Against SQKD Vulnerability

Compared to known classical security key vulnerabilities, SQKD possess more devastating disadvantages as follows

  • Silent and stealthy: Unlike other attacks, PNS leaves no detectable trace on the transmitted signal, making it particularly insidious.
  • Availability to exploit: Currently available practical quantum key distribution (QKD) systems use weak lases indicating the devastating nature of mass implementation of SQKD.

Experts have proposed a limited number of solutions to address the threat.

  • Decoy state protocols: By sending “decoy” pulses with known photon numbers alongside the actual signal, the sender can statistically detect attacker’s interference and abort the communication if necessary.
  • Single-photon sources: Developing source which can accurately emit single-photons can minimize the prevalence of multi-photon pulses, reducing the attack surface for PNS.

PNS represents a critical challenge in the ongoing quest for secure quantum communication. Understanding its mechanics and implementing effective countermeasures is crucial for realizing the full potential of this revolutionary technology.

Recent Findings on Decoy States

Researchers conducted an experiment to evaluate the safety of SQKD when using a weak laser. They determined that highly attenuated lasers and threshold detectors can still safely utilize the method at a range of 150 km. The findings of the research define the limits of SQKD more accurately ensuring secure key distribution. It can further assist to improve the security measurements of quantum technology.

The Future of QKD

Effective key distribution is the backbone of any data security system. Traditional encryption methods, though robust, face a looming threat from the rising potential of quantum computers. By exploiting the inherent randomness and fragility of quantum states, QKD guarantees an unbreakable encryption key exchange. Any attempt to eavesdrop on the quantum signal inevitably disturbs it, leaving a telltale sign and alerting the sender and receiver. This “quantum eavesdropping detection” renders QKD immune to the vulnerabilities of classical cryptography.

This revolutionary quantum technology holds immense potential in various sectors:

  • Financial institutions: Safeguarding private customer data and very sensitive financial operations.
  • Government organisations: Maintaining safe communication for vital infrastructure and information exchanges in order to protect the country’s security.
  • Healthcare: Protecting patient privacy and facilitating safe medical record transmission.
  • Critical infrastructure: Defending against cyberattacks on control systems for transport networks, electricity grids, and other essential infrastructure.
  • Beyond the exchange of keys: The application of QKD goes beyond key exchange. It opens the door to a network connected by quantum channels that is impervious to hacking efforts, a future-proof quantum internet. This promises a new era of secure communication, collaboration, and information exchange.

Challenges and Advancements in QKD

  • Cost and complexity: QKD systems face constraints in achieving widespread adoption due to their relatively high cost and technical complexity.
  • Limitations on distance: Long-distance deployments of quantum signals require repeaters or new protocols because the quality of these signals deteriorates with distance.
  • Standardisation: Establish industry-wide standards to ensure interoperability and a smooth transition into the current infrastructure.

Researchers continually make significant advancements to address these challenges.

  • As a result of technological advancements, QKD components are becoming more affordable and smaller, increasing accessibility to the technology.
  • Research into long-distance QKD solutions, such as satellite and free-space communication, has the potential to increase the technology’s reach.
  • Groups like the Quantum-Safe Cryptography Standardisation Initiative (QCSI) are actively defining industry-wide standards for Quantum Key Distribution (QKD).

The future of QKD is bright. As the technology matures and overcomes its present hurdles, it will become an indispensable tool for securing our digital world in the quantum age. This technology will impact industries, safeguard critical infrastructure, protect sensitive data, and enable a new era of secure communication and collaboration.

Source : https://doi.org/10.1140/epjqt/s40507-023-00175-0

Dr Sukitha Kothalawala - Author
Dr Sukitha Kothalawala
PhD in Materials Engineering, University of Queensland
Jan. 13th, 2024 — 4m read

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