Quantum Communications in Space

The modern world more and more relies on information exchange using data transfer technologies.

Words and phrases such as “5G”, “internet of things”, “blockchain”, “Bitcoin”, “Artificial Intelligence”, “Big Data Analytics” and “qubit” are often used in every day conversation, despite people not always understanding their meanings. Private and secure communications are fundamental for the Internet, national defence and e-commerce, thus justifying the need for a secure network with the global protection of data. Information exchange through existing data transfer channels is becoming prone to hacker attacks causing problems on an international scale, such as interference with democratic elections, etc. The apocalyptic scenario of hackers’ breaching national cyber-security has even been used as the premise for Hollywood action thrillers such as “Swordfish” in 2001 and “Live Free or Die Hard in 2007, raising public awareness albeit in a misleading way.

In reality the scale of the “hacking” problem is continual, in 2019 British companies were reportedly hit by about 5,000 “ransomware” attacks that paid out more than £200 million to cyber criminals [1]. During the first half of 2020, $144.2 million has already been lost in 11 of the biggest ransomware attacks [2]. Communications privacy is therefore of great concern at present.

The reasons for the growing privacy concerns are [3]: the planned increase of secure information (requiring encryption) data traffic rates from the current 10 to future 100 Gbit/s; annual increases in data traffic of 20-25% and the application of fibre optic cables not only for mainstream network lines by also for the “final mile” to the end-user. These developments are accompanied by [3]: growing software vulnerabilities; more powerful computational resources available to hackers at lower costs; possible quantum computer applications for encryption cracking and the poor administration of computer networks.

Conventional public key cryptography relies on the computational intractability of certain mathematical functions.

Applied conventional encryption algorithms (DH, RSA, ECDSA TLS/SSL, HTTPS, IPsec, X.509) are good in that there is currently no way to find the key (with a sufficient length) for any acceptable time. Nevertheless, in principle it is possible, and there are no guarantees against the discovery in the future of a fast factorization algorithm for classical computers or from the implementation of already known algorithms on a quantum computer, which will make conventional encryption “hacking” possible. Another “hacking” strategy involves original data substitution. A final vulnerability comes from encryption keys being potentially stolen. Hence, the demand exists for a truly reliable and convenient encryption system.

Quantum communications are expected to solve the problem of secure communications first on international and national scales and then down to the personal level.

Quantum communication is a field of applied quantum physics closely related to quantum information processing and quantum teleportation [4]. It’s most interesting application is protecting information channels against eavesdropping by means of quantum cryptography [4].

Quantum communications are considered to be secure because any tinkering with them is detectable. Thus, quantum communications are only trustful and safe in the knowledge that any eavesdropping would leave its mark.

By quantum communications two parties can communicate secretly by sharing a quantum encryption key encoded in the polarization of a string of photons.

This quantum key distribution (QKD) idea was proposed in the mid-1980s [5]. QKD theoretically offers a radical new way of an information secure solution to the key exchange problem, ensured by the laws of quantum physics. In particular, QKD allows two distant users, who do not share a long secret key initially, to generate a common, random string of secret bits, called a secret key. Using the one-time pad encryption, this key has been proven to be secure [6] to encrypt/decrypt a message, which can then be transmitted over a standard communication channel. The information is encoded in the superposition states of physical carriers at a single-quantum level, where photons, the fastest traveling qubits, are usually used. Any eavesdropper on the quantum channel attempting to gain information of the key will inevitably introduce disturbance to the system that can be detected by the communicating users.