QNu Labs, in collaboration with BISAG-N and IIT Gandhinagar, has conducted field tests of a 5.56-kilometer quantum key distribution (QKD) line in free space.

The keys generated during the test were utilized alongside post-quantum cryptography (PQC) for the encryption and decryption of test messages.

Quantum Channel Through the Atmosphere

The experiment took place overnight from September 27 to 28, connecting the BISAG-N and IIT Gandhinagar sites in Gujarat. Instead of using fiber optics, the participants transmitted quantum signals through the atmosphere, employing QNu Labs’ Pointing, Acquisition and Tracking (PAT) system to accurately direct the optical channel.

During the trial, the quantum bit error rate (QBER) remained below 5%, with a secure key generation rate ranging from 230 to 260 bits per second. According to India’s Ministry of Electronics and IT, this marks the first demonstration of a free-space QKD channel of this magnitude in the country.

Integration of QKD with Post-Quantum Cryptography

A significant aspect of the trial was not only the transmission of quantum keys but also their integration with QNu Labs’ Vedic Kavach software, which supports PQC and the generation of quantum random numbers.

The system featured dual layers of protection. QNu Labs’ Armos device provided a hardware QKD channel, while Vedic Kavach offered a software layer based on post-quantum cryptographic algorithms. The resulting 256-bit keys were transmitted via the ETSI GS QKD 014 interface, allowing for the successful encryption, transmission, and decryption of a test message.

This architecture is designed to function even if the quantum channel becomes temporarily unavailable, indicating that QKD and PQC are viewed not as competing technologies but as complementary layers of security.

From 5.56 km to Satellite Communication

The participants view the tests as a stepping stone towards longer quantum channels. They aim to leverage the insights gained to develop multi-kilometer networks, increase the number of nodes, and eventually facilitate satellite quantum communication.

It is worth noting that in September, Sparkle and the European space communication operator Hellas Sat established a quantum-resistant satellite link between Greece and Cyprus.

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