The race for quantum technology is increasingly intriguing. Google and IBM are beginning to develop quantum computers that would revolutionize computing at speeds now inconceivable. A much-awaited strength of quantum technology lies in cryptography. With the proliferation of IoT and the next 5G, it is extremely important to create secure channels. In contrast, quantum channels that carry information have security protocols built into the encrypted data. Each channel is uniquely different from one another, allowing the risk of interception during transmission to be reduced.

The safest and most widely used methods to protect the confidentiality and integrity of data transmission are today based on symmetric cryptography, while an even more reliable security is provided with a form of mathematically unbreakable cryptography called "one-time pad", in whereby the data is encrypted using a random key of the same length as the encrypted data.

With quantum cryptography, all the cryptographies techniques of today would be void. Today, in order to decrypt confidential, encrypted information, it is necessary to have the relative private key. And today, running a so-called "brute force" attack - trying all the possible combinations of letters, special characters and numbers - would be impossible to decipher an RSA key, because the computers we have available would take too long. With quantum technology, however, the same operation would take a few seconds.

Researchers at Nanyang Technological University in Singapore (NTU Singapore) have developed a quantum chip 1,000 times smaller than current quantum configurations. Led by Professor Liu Ai Qun of the NTU and associate professor Kwek Leong Chuan, the team's results were published in Nature Photonics.

The results offer a new opportunity for implementing quantum cryptography methods in many financial systems. This new chip will improve the security context in the various communication methods, from the withdrawal of cash from the ATM to the purchase of goods online (figure 1). These are technologies that today are not very safe and whose communications can be intercepted. Only 3-4 mm wide, the chip uses quantum communication algorithms and provides a higher level of security than existing standards thanks to quantum key distribution (quantum key distribution, QKD).

The Quantum Key Distribution (QKD) uses quantum properties for the exchange of secret information, such as an encrypted key, which can then be used to encrypt messages transmitted over an insecure channel. The security of the QKD is based on fundamental laws of nature and physics, which are invulnerable to increasing computing power, new attack algorithms, or quantum computers.

In the case of quantum cryptography, the key (the medium that allows a message to be encrypted and thus to become readable again) is encoded in a series of photons that are passed between the two parties who must share a message (for example through the optical fiber). According to the Heisenberg uncertainty principle (for which, simplifying, it is not possible to know two characteristics of a quantum object at the same time), anyone interested in obtaining the key cannot do it without disturbing these (polarized) photons. In fact, that is, anyone who interferes between the communication alters their characteristics, leaving a footprint that allows them to notice the intrusion to the interested parties.

Prof Liu, who is from NTU's School of Electrical and Electronic Engineering, said, "In today's world, cybersecurity is very important as so much of our data are stored and communicated digitally. Almost all digital platforms and repositories require users to input their passwords and biometric data, and as long as this is the case, it could be eavesdropped on or deciphered. Quantum technology eliminates this as both the password and information are integrated within the message being sent, forming a quantum key."

Quantum chip

Figure 1: the tiny 3mm quantum communication chip [Source: NTU Singapore]

The discoveries that quantum calculus could bring in areas such as artificial intelligence, medical diagnostics, and pharmacological therapies, just to name a few, are difficult even to imagine or predict would be a real IT revolution. A quantum computer is instead a tool where the number of operations required to achieve a particular result is exponentially lower. Innovation is not in the greater speed of every single operation, but in the smaller number of operations required to reach the result.

The security of our information, however, risks being thrown into crisis by the advent of future quantum computers, equipped with large computing resources, potentially able to overcome current cryptographic techniques. For this reason, quantum cryptography and post-quantum cryptography will become increasingly important.