In the coming years, large-scale quantum computers will make most of the current cryptography techniques insecure. To avoid this, two major global directions are being pursued.

In the digital age, every day each one of us carries out activities that would be impossible without cryptographic techniques. The security of our information, however, risks being thrown into crisis by the advent of future quantum computers, equipped with vast computing resources, potentially able to overcome current cryptographic techniques. A new generation of devices under development by companies such as Microsoft, Google and IBM, which will multiply the computing capabilities of computers, and will probably make obsolete the encryption systems currently in use, based on the transmission of radio waves.

Quantum cryptography is a method of transmitting secret information that offers the guarantee of maximum security. Unlike conventional cryptography based on calculation hypotheses, quantum cryptography has a significant advantage: its security is based on the laws of physics proving to be unconditionally safe with quantum cryptographic techniques. Quantum mechanics aims to describe the heart of matter, where natural phenomena occur on a subatomic scale. Current systems of Quantum Cryptography rely on encoding a computer bit in a property of a single photon, which is the fundamental constituent of light and electromagnetic radiation.

The collaboration agreement between Imec and the National University of Singapore (NUS) aims to jointly develop scalable, robust, and efficient quantum technologies for the distribution of secure keys for the internet of the future. In the coming years, large-scale quantum computers will make most of the current cryptography techniques insecure. To avoid this, two major global directions have been pursued: a post-quantum cryptography approach and another hardware-based approach called quantum cryptography.

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Post-quantum cryptography is essentially about updating existing algorithms and cryptographic standards. It still maintains a security profile that is still based on unproven hypotheses. It consists of the definition and the study of cryptographic systems capable of guaranteeing high levels of security even against attackers equipped with quantum computers. The first challenge in this area consists of identifying mathematical problems that are difficult to solve for an attacker who is not significantly affected by the existence of quantum computers.

Quantum cryptography, on the other hand, offers a much stronger security guarantee. With this approach, two essential constitutive elements are the quantum key distribution (QKD) and the quantum random numbers generation (QRNG). Now, however, the methods and processes that enable these quantum technologies are limiting and expensive. As a result, these bottlenecks have made quantum cryptography unattractive for widespread diffusion. Imec and NUS aim to solve some of these bottlenecks (Figure 1).

*Figure 1: block diagram of quantum cryptography*

“Our approach consists of developing and integrating all QKD key components in a single silicon-photonics based chip, which ensures a cost-effective solution,” said Joris Van Campenhout, R&D Program director at imec. Dr. Charles Lim, Assistant Professor at NUS said: “The development of chip-based prototypes will allow us to turn today’s QKD technologies into an efficient communication networking solution.

The quantum distribution of keys makes it possible to transmit a secret key from one user to another, reaching the condition of perfect secrecy from a mathematical point of view, and therefore making any interception attempts useless. Furthermore, the quantum characteristics of the physical phenomena used make it intrinsically inevitable to detect the presence of any passive attackers. Quantum Cryptography is an alternative to the use of Public Key protocols, such as RSA, to generate and exchange secret keys.

The objective of QKD is to guarantee the secrecy of a distributed key. In turn, legitimate subjects can use this key for encryption. The confidentiality of the transmission data is guaranteed by a systemic chain through the quantum-distributed key and the encryption algorithm. If one of these two "parameters" fails, the entire chain is compromised.

Quantum cryptography is thought to be secure for various reasons. One, the quantum no-cloning states that an unknown quantum state cannot be cloned. Moreover, in a quantum system, which can be in one of the two states, any attempt to measure it will disturb the system itself. If a quantum message is intercepted by malicious users, it will become useless to the recipient. The measurements of a quantum property are irreversible, which means that the quantum message cannot return to its original state.

Fundamentally, the no-cloning theorem protects the uncertainty principle of quantum mechanics, effectively representing an essential ingredient in quantum cryptography, prohibiting interceptors from creating copies of a transmitted quantum cryptographic key.

The futuristic vision of a quantum communication with the QKD implementation could be the ideal choice, also given the advent of quantum computers and therefore of optoelectronics/photonics (Figure 2).

*Figure 2: classical and quantum communication*

Cryptography is increasingly considered a protection tool for cyber security, becoming essential for banks and financial institutions that, being responsible for managing a large amount of sensitive data, are confirmed as one of the main objectives of cyber attacks.