1. Overview¶

1.1. Background¶

Quantum Key Distribution (QKD) promises quantum secret keys that are unpredictable and indeterministic. But the transient (one-time-use) and point-to-point nature of QKD is not suitable for all types of use cases.

Store-and-forward protocols (e.g., secure email), permanent storage (e.g., file transfer), periodic usage (e.g., payment master keys) are some use cases that will benefit from using quantum secret keys, but require a more persistent means to store these keys for subsequent usage.

This is where QKDLite comes in. Using QKDLite together with a Hardware Security Module (HSM) infrastructure and a QKD infrastructure, we are able to bridge the difference in key management requirements between what QKD provides versus what business applications need.

QKDLite also supports quantum-safe communications alongside existing HSM and QKD infrastructures. This is achieved with the seamless integration of pQCee’s quantum-safe TLS proxy, which acts as a bridge to enable quantum-safe protocols with QKDLite nodes while maintaining backward compatibility with classical Transport Layer Security (TLS) provided in existing IT infrastructure.

1.2. Key Terms and Concepts¶

This manual uses key words and concepts from the quantum cybersecurity domain, in particular, from the ESTI standards context. For readers who are not familiar in this area, you are encouraged to read this section before proceeding to the other parts of the manual.

1.2.1. Quantum Key Distribution Entity¶

The Quantum Key Distribution Entity (QKDE), usually, refers to a QKD hardware appliance that provides quantum key distribution function. A minimum of two QKDEs are required to perform quantum key distribution to each other using QKD protocols. At the end of the QKD process, both QKDEs will possess knowledge of the same quantum secret key.

1.2.2. Quantum Random Number Generator¶

The Quantum Random Number Generator (QRNG) is a device that utilises a quantum physical process to generate (quantum) secret keys. A QRNG can also be considered as a True Random Number Generator or a Hardware Random Number Generator.

1.2.3. Quantum-safe Communications¶

Network communications between computers on the internet today largely relies on secure communications protocols (e.g., TLS and SSH) that utilises classical ciphers to secure network data. Quantum-safe communications, are secure communication protocols that utilises post-quantum cryptography (PQC) ciphers to secure network data. Some examples of PQC ciphers are ML-KEM (aka Kyber) and ML-DSA (aka Dilithium).

1.2.4. Security Application Entity¶

The Security Application Entity (SAE) refers to a software or device that performs a security function. An SAE can be standalone or work together with other SAEs as a group to perform a security function.

1.2.5. Key Management Entity¶

The Key Management Entity (KME) is a software application or hardware device that performs key management operations, such as handling requests for new secret keys from business applications or SAEs. QKDEs and QKDLite nodes can function as a KME for others to request for quantum secret keys.

1.3. Technical Architecture¶

A QKDLite node connects to both a HSM appliance to a QKD appliance. A QKDLite node can connect to another QKDLite node, in a daisy-chain configuration, to provide key activity replication from the main node to the rest of the nodes down the chain.

Each QKDLite node contains the core QKDLite software package, which consists of:

QKDLite Transport Key Utility - a program named Insert2HSM that inserts a Transport Key into the HSM. The Transport Key is a 256-bit random key to wrap exported keys or unwrap imported keys. Multiple HSMs having the same Transport Key are able to replicate keys across one another.
QKDLite Utility - a program named QKD2HSM that interfaces with both HSM appliance and QKD appliance to generate and push QKD keys into the HSM. The QKDLite Utility can also be used to list and delete keys in the HSM.
QKDLite Scripts - a suite of shell scripts that facilitate key management workflows via the QKDLite Utility and perform fail-safe replication of key activity across QKDLite nodes.

QKDLite nodes connect to one another using quantum-safe SSH. A QKDLite node uses a quantum-safe key encapsulation algorithm to securely send sensitive key material to HSM appliances. The QKDLite node uses quantum-safe TLS to communicate with QKD appliances.

1.4. Deployment Configuration¶

QKDLite is designed for seamless integration with network appliances that support the quantum-safe TLS. This deployment scenario is described in Configuration #1 below.

Although some network appliances are limited to classical TLS, quantum-safe TLS can be achieved by placing a pQCee Quantum-safe TLS Proxy in front of the network appliance. This deployment scenario is described in Configuration #2 below.

1.4.1. Configuration #1: QKDLite with PQC TLS Capable Appliance¶

        block-beta
   columns 7

   space
   space

   block
      columns 1
      UAA["Business App"] HA["HSM A"]
   end

   space

   block
      columns 1
      UAB["Business App"] HB["HSM B"]
   end

   space

   block
      columns 1
      UAC["Business App"] HC["HSM C"]
   end

   space space space space space space space

   QM["QKDLite Management"]
   space QA["QKDLite Node A"]
   space QB["QKDLite Node B"]
   space QC["QKDLite Node C"]

   space space space space space space space

   space
   space

   block
      columns 1
      KA["KME A"] SA["SAE A"]
   end

   space

   block
      columns 1
      KB["KME B"] SB["SAE B"]
   end

   space
   space

   QM --"PQC SSH"--> QA
   QA --"PQC SSH"--> QB
   QB --"PQC SSH"--> QC
   QA --"PQC payload"--> HA
   QB --"PQC payload"--> HB
   QC --"PQC payload"--> HC
   QA --"PQC TLS"--> KA
   QB --"PQC TLS"--> KB
   SB --> SA
   SA --"QKD"--> SB

Each HSM Entity consists of a Business App and the HSM appliance itself. The Business App consumes secret keys from the HSM appliance to perform secure business transactions daily.

The QKD Entity consists of a Key Management Entity (KME) and a Secure Application Entity (SAE). QKDLite interfaces with the KME to derive new QKD quantum key material between a pair of connected SAEs.

Within each QKD-enabled site, QKDLite communicates with both HSM and KME to generate and store QKD quantum secret keys. QKDLite can be paired to replicate key management activity from one site to another site in a quantum-safe and fail-safe manner. This pairing can also be extended to sites without access to a QKD infrastructure.

In the context of a triple-site-replication setup, QKDLite can be deployed to HSM and QKD infrastructures as shown in the diagram above. Site A (left column containing HSM A) and Site B (middle column containing HSM B) are operational HSM sites located in regions that have connections to a common QKD infrastructure. Site C (right column containing HSM C) is an operational HSM site located in a different region that has no QKD infrastructure. QKDLite replicates key management activity from Site A to Site B, and from Site B to Site C. In this manner, although Site C has no access to a QKD infrastructure, QKD quantum secret keys remain accessible to the Business App at Site C.

1.4.2. Configuration #2: QKDLite with pQCee Quantum-safe TLS Proxy¶

        block-beta
   columns 7

   space
   space

   block
      columns 1
      UAA["Business App"] HA["HSM A"]
   end

   space

   block
      columns 1
      UAB["Business App"] HB["HSM B"]
   end

   space

   block
      columns 1
      UAC["Business App"] HC["HSM C"]
   end

   space space space space space space space

   QM["QKDLite Management"]
   space QA["QKDLite Node A"]
   space QB["QKDLite Node B"]
   space QC["QKDLite Node C"]

   space space space space space space space

   space space PA["PQC TLS Proxy A"] space PB["PQC TLS Proxy B"] space space

   space space space space space space space

   space
   space

   block
      columns 1
      KA["KME A"] SA["SAE A"]
   end

   space

   block
      columns 1
      KB["KME B"] SB["SAE B"]
   end

   space
   space

   QM --"PQC SSH"--> QA
   QA --"PQC SSH"--> QB
   QB --"PQC SSH"--> QC
   QA --"PQC payload"--> HA
   QB --"PQC payload"--> HB
   QC --"PQC payload"--> HC
   QA --"PQC TLS"--> PA
   QB --"PQC TLS"--> PB
   PA --"Classical TLS"-->KA
   PB --"Classical TLS"-->KB
   SB --> SA
   SA --"QKD"--> SB

The deployment setup is similar to Configuration #1 earlier with one difference: the inclusion of pQCee Quantum-safe TLS Proxy.

pQCee Quantum-safe TLS Proxies will be co-located with the QKD appliances in a higher trust zone and will front all external incoming traffic on behalf of the QKD appliances. QKDLite will communicate with the QKD appliances using quantum-safe TLS via these proxies, thus enabling quantum-safe communication with the QKD appliances.