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Quantum Key Distribution as a Service and Its Injection into TLS

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Information Security Practice and Experience (ISPEC 2023)


Quantum key distribution (QKD) is a key agreement method that relies on the laws of physics and ensures that the keys have not been eavesdropped on or modified by a third party. While commercial QKD devices are available, they are expensive, require specific infrastructure, and have high operational expenses. In this paper, we propose an architecture and a set of protocols that allow us to implement QKD as a service (QaaS). End users communicate with QaaS via classical TLS channels secured with post-quantum cryptography (PQC). We show how to further strengthen the security of these classical links to make them sustainable to active attacks (classical and quantum) on any single segment of QaaS. We also show how to integrate QaaS into the state-of-the-art TLS 1.3 protocol. As a result, QKD becomes available for a larger community of end-users. Furthermore, we show how QaaS can reduce the number of digital signatures within a TLS 1.3 handshake, which is essential since post-quantum signatures are much longer than the conventional RSA/ECC-based ones.

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  1. 1.

    Coherent One-Way protocol, patented by IDQ.

  2. 2.

    e.g., Toshiba Multiplexed and Long Distance, IDQ Clavis and Cerberis series, QTI Quell-X, LuxQuanta NOVA LQ, KEEQUANT Andariel, SeQre Aurora and Eclipse.

  3. 3.

    unless the link is physically broken, a hardware failure occurs, or there is constant eavesdropping or intrusion.

  4. 4.

    quantum random number generator.

  5. 5.

    One of the benefits of the equivalence property is that there is no advantage in attacking either of KDCs. Another benefit is the ability to design algorithms and protocols that can purposely choose the first receiver of the reserveKeyAndGetKeyHalf message.

  6. 6.

    TLS 1.3 terminology; actually, it is a key exchange method.

  7. 7.

    We choose T such that each of the three connections at the longest path (Aija \(\leftrightarrow \) User 1 \(\leftrightarrow \) User 2 \(\leftrightarrow \) Brencis) can survive the maximal TCP back-off; \(T\approx 3\times 30\) s \(\approx 3\times \) TCP re-transmission timeout for five tries.

  8. 8.

    A key is called a “zombie” if it is being stored at one KDC endpoint but is not present at the other, i.e., it has been reserved and deleted or hasn’t been received at all (due to server restart or network interruption). “Zombie” keys can also be deleted before TTL expires, e.g., by the Control Protocol.

  9. 9.

    e.g., due to too many key reservation requests or due to some technical failure, when new keys stop appearing from the QKD device.

  10. 10.

    A client can generate a key pair by himself and send a certificate signing request (CSR) to the CA, or the whole process can be performed by the CA.

  11. 11.

  12. 12.

    Technically, any string, e.g., a URI, can be used to identify the communicating parties. In this paper, we use the term “domain name” to represent such strings.

  13. 13.

    In the case of client certificates, the traditional certificate-based domain name validation is performed. In the case of JWT tokens, the check is performed by a database lookup or by verifying the hash-based JWT signature.

  14. 14.

    BouncyCastle provides pure Java implementations of cryptographic primitives, including the majority of PQC algorithms from NIST Rounds 3 and 4 in the latest releases. BouncyCastle can be downloaded from

  15. 15.

    Our scripts for building such HAProxy are available at

  16. 16.

    We used the same approach in our quantum random number generator service [15].

  17. 17.

    We use TLS v1.3 since it supports KEMs and reduces the number of round-trips in a TLS handshake. KEMs are promoted by NIST, while TLS is an IETF standard supported by all browsers and networking libraries.

  18. 18.

  19. 19.

    NIST PQC Round 3 winner, to be standardized.

  20. 20.

    NIST PQC Round 3 candidate, not participating in Round 4 but invented by renowned scientists.

  21. 21.

    since it is a standard, which is already being used for keys and certificates.

  22. 22.

    thus, hash functions can be upgraded in the future.

  23. 23.

    See also:

  24. 24.

    See also: and


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Research supported by the European Regional Development Fund, project No. “Applications of quantum cryptography devices and software solutions in computational infrastructure framework in Latvia”.

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Correspondence to Sergejs Kozlovičs .

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Kozlovičs, S., Petručeņa, K., Lāriņš, D., Vīksna, J. (2023). Quantum Key Distribution as a Service and Its Injection into TLS. In: Meng, W., Yan, Z., Piuri, V. (eds) Information Security Practice and Experience. ISPEC 2023. Lecture Notes in Computer Science, vol 14341. Springer, Singapore.

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