New way to improve the security of quantum cryptography

US, WASHINGTON (ORDO NEWS) — Scientists at the NTI Quantum Communications Competence Center Consortium, which includes specialists from NUST MISiS, have developed a way to increase the security level of quantum cryptography. Thanks to a special verification algorithm, extraneous “noises” that can affect the random number generator operation are allocated and deleted. This completely excludes the possibility of external influence on the encryption process.

An article on development is published in Optics Express magazine. Behind every process of sending and receiving information in the modern world is cryptography – a data encryption system that ensures their security. The most common is the so-called asymmetric encryption, which uses not one secret key, but two: public and private.

The private (secret) key is stored only at one of the participants of the cryptographic system who wants to receive an encrypted message. To do this, he sends a public key through a regular (non-classified) information channel, which is used to encrypt the message. To decrypt the message, it is not enough to have only the public key – you need to know the private key also.

This situation is similar to the fact that if a person, wanting to receive a secret message, distributed small locks to everyone, but would not give anyone the keys to these locks. Anyone who would like to share their secret with him could put a secret message in the box and lock it with this lock. Obviously, now no one except him will be able to open the box and read the secret message, even if the box falls into the hands of the attacker.

The asymmetric encryption system relies on an unproven mathematical statement about the impossibility of decomposing an integer into simple factors in polynomial time. Therefore, it is believed that the power of a modern computer is not enough to crack such a system, however, such a possibility may appear in the near future with a quantum computer. This casts doubt on the safety of classical cryptography techniques in the approaching era of quantum superiority.

In contrast to the possible technologies of quantum hacking, scientists are actively developing and implementing methods of quantum cryptography – encryption based not on computer algorithms, but on the laws of quantum mechanics. Quantum cryptography systems solve the problem of securely distributing a secret key between participants in a cryptographic system. The secret key is transmitted through the optical channel using single photons.

According to the laws of quantum mechanics, an attacker will not be able to quietly intercept individual photons, so that any time he tries to find out the secret key, the system will signal a danger. In addition to the source and detector of single photons, an important element of the quantum cryptography system is the so-called quantum random number generator. Since the attacker cannot intercept single photons, he can try to attack precisely this element of the system.

Researchers at the NTI Quantum Communications Competency Center Consortium (NUST MISiS, QRate, and the Russian Quantum Center) have developed a way to increase the security level of quantum cryptography systems using a special algorithm that can detect attacks against a quantum random number generator.

To generate random bit sequences, scientists proposed using noise arising in a semiconductor laser and associated with spontaneous emission. Since spontaneous emission is caused by the so-called zero-point oscillations of the electromagnetic field, it can be argued that such noises in the laser are of a purely quantum nature, and therefore it is fundamentally impossible to learn to predict them and, most importantly, they are immune to any attempts to “subordinate” them to external control .

However, since it is impossible to directly use these noises without conventional (classical) measuring instruments, quantum noises are “polluted” with classical noises that an attacker could potentially use to compromise random bits obtained with the help of these noises.

Scientists from the company QRate and NUST “MISiS” have developed a protocol that allows on-the-fly to evaluate the contribution of classical noise and thus determine the level of potential threat. Moreover, the protocol they proposed allows us to convert the output random bit sequence to “true quantum” without the use of complex post-processing algorithms such as hashing, which are usually used for these purposes. According to the developers, their algorithm can now be used in existing and planned quantum random number generators for quantum cryptography installations.

The competence center of the STI “Quantum Communications” was created in 2018 by the NUST “MISiS” and the Russian Quantum Center. The consortium also included the Steklov Institute of Mathematics, RANEPA, TSU, as well as small innovative enterprises specializing in quantum communications, including QRate.

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The article is written and prepared by our foreign editors from different countries around the world – material edited and published by Ordo News staff in our US newsroom press.