La Voz de
Galicia interviews Víctor Zapatero.

Víctor Zapatero, researcher: «In cryptography, grossness translates into security gaps»

For eight years, Víctor Zapatero has been working at Atlanttic, University of Vigo, doing research on quantum communications. For the last three years, he has been a postdoctoral researcher at the Vigo Quantum Communication Center. Recently, together with his team, he has developed a quantum communication system awarded by the “Real Academia das Ciencias” as the best research in technical sciences of Galicia. Regarding this award, he says he is “proud to be recognized in this way”, because the scientific career “is full of sacrifices and uncertainty”.

Why is it important for institutions to improve their encryption processes?

If an institution wants to ensure the confidentiality of its communications, then it must encrypt them. This involves altering a message to make it unintelligible to everyone except to an authorized recipient who must have a key enabling the retrieval of the original message. This causes a problem: the sender must exchange a key with the receiver reliably. Quantum key distribution is the only mathematically secure way to exchange a key through an insecure channel.

And how does quantum mechanics apply to this encryption procedure?

Quantum mechanics describes the behaviour of matter and radiation on very small scales. According to quantum mechanics, the information stored in a system at this scale cannot be copied. An example would be the photon, which is the indivisible unit of light. Imagine that I encode a 0 or a 1 in the polarization of a photon and send it to you. If someone tried to intercept the photon along the way to copy the encoded value, he/she would modify it statistically. Then, we would know that there is an eavesdropper. Ideally, by repeating this process for long enough, I could send you a secret key, that is, a random list of zeros and ones, with the certainty that no one else knows it.

You assure that this system is very expensive and that, moreover, it can lose its security guarantees if it is not implemented well.

In my opinion, the fundamental difficulty is common with other technologies, that we are very large creatures. Making quantum key distribution would be simple if we could precisely manipulate atomic-sized systems, but these are about one millionth of a centimeter or smaller. Our size makes us gross for this task and, in cryptography, grossness translates into security gaps.

And is your research proposal a simpler variant of this process?

What we have proposed is a passive quantum key distribution system, whereas the present systems are active. In an active system, a random number generator encodes the secret information into light pulses using optical modulators (devices that control the characteristics of a beam of light). On the contrary, in a passive system a quantum interference mechanism sequentially generates signals in a genuinely random way, and later on, the rounds of interest are filtered. This variant is more practical because it avoids the use of random number generators and optical modulators, whose functioning limits the frequency of operation of the system. In addition, by avoiding these modulators, a passive system circumvents certain leaks of information and is more robust to hacking attacks.

What new research paths will you take in relation to the new variant proposed by your team?

For the time being, we have done a couple of other theoretical works that extend the applicability of this variant, and we have even collaborated in the first experimental demonstration of our passive scheme, carried out by a group from the University of Science and Technology of China. However, the future of this line of research is yet to be determined.

Iago Castro-Pérez, La Voz de Galicia.

For more information, please visit: Víctor Zapatero, investigador: «La torpeza en criptografía se traduce en lagunas de seguridad»