How India plans to make satellite communication hack-proof

The Indian Space Research Organisation (ISRO) aims to launch a satellite with ultra-secure quantum communication capabilities. The system is expected to be impenetrable by hackers.

The satellite, based on Quantum Key Distribution (QKD) or quantum cryptography, will contribute to the creation of a communication network, which connects quantum computers processing information in unison. The agency is yet to announce a launch date.

Though QKD is not yet recommended for secure communication by the US National Security Agency or endorsed for government or military applications by the United Kingdom's National Cyber Security Centre, India has decided to invest in the technology in the face of increasing global quantum computing power, which can easily disrupt conventional encryption methods. The level of investment, however, will be difficult for a country like India, and it may take about ten years to develop QKD as a standard.

The basic idea of QKD is to use the quantum states of photons to share secret keys between two distant parties. Therefore, photonic quantum computers, based on or using quantum states of photons, could be the most efficient choice, offering a seamless integration of communication and computing. India needs to act fast in developing a state-of-the-art laboratory devoted to photonic platforms for quantum computing and other possibilities.

QKD uses principles of quantum mechanics to generate and distribute keys that can encrypt messages, audio, video, or text. Communication through quantum states, and measuring associated physical observables, is the backbone of QKD.

In 2021, ISRO and Physical Research Laboratory (PRL), Ahmedabad successfully demonstrated free-space quantum communication over a distance of 300 metres through live video conferencing using quantum-key-encrypted signals between two buildings inside the Space Applications Centre, Ahmedabad campus. The sender could encrypt a file (audio, video, text) while the receiver could decrypt it using the same quantum keys generated at both ends in real time. Free-space QKD is a precursor to satellite-based QKD.

In 2022, PRL showed quantum entanglement-based real-time QKD over a 300-metre atmospheric channel featuring quantum-secure text, image transmission and quantum-assisted two-way video calling. PRL also observed the effect of atmospheric aerosols on the key rate. Single photons and entangled photons — at the heart of photonic quantum computing —were used in these demonstrations.

Why tighter encryption is needed in a quantum world

Current encryption schemes based on mathematical calculations are easy to hack for someone with quantum computing knowledge — putting personal data, strategic national secrets, and online financial transactions at risk. But using QKD to encrypt messages makes it impossible even for experts in quantum computing to decrypt.

We need secure communications on a larger scale wherever we move or connect through phones. In the age of mobile phones and enhanced mobility, securing messages between two or more stations does not make sense. We need to have a global quantum communication network.

Our current network relies on optical fibres; information loss in transmitting quantum signals over long distances is one of the challenges of quantum communication. These losses occur due to inherent properties of the fibre material itself, such as absorption and scattering. In classical communication, one can compensate for these losses by amplifying the signal. However, amplifying signals in the form of quantum states is impossible because quantum mechanics prevents making a perfect copy of an arbitrary state, the cornerstone for preventing eavesdropping.

Satellite-based quantum communication can overcome this limitation by distributing quantum states to far-off ground stations and keys for secure transmission.

Quantum communication over long distances

China led satellite-based QKD by launching the Micius satellite in 2016. In 2017, scientists at the Chinese Academy of Sciences in Beijing and the Austrian Academy of Sciences in Vienna used a satellite link to carry out the world's first intercontinental quantum-safe video chat. The country has the largest space-to-ground quantum communication network with three satellites and four ground stations.

In 2015, Japan was the first to send a very compact payload for QKD on a microsatellite SOCRATES, though results from the voyage were published in July 2017. Although Germany didn't launch a satellite or payload, it used a plane to demonstrate QKD from space to ground in 2012. Italy was the first to report satellite-to-ground QKD using satellite retroreflectors in 2015.

India’s quantum-based satellite will likely use the BB84 (encoding every bit of the secret key in the polarization state of a single photon) and BBM92 (use of entangled photon pairs) quantum key distribution protocols.