At the forefront of multimedia and security standards

Just as it is convenient when the same standards are used worldwide for weights and measures, or for shipping containers, it is convenient in the digital world when the same standards are used for things like multimedia and security software. Digital standards make the exchange of videos and the development of security software easier and guarantee a certain quality or security level.

In 2022 the U.S. National Institute of Standards and Technology (NIST) selected four new cryptographic schemes as upcoming standards for public-key encryption and digital signatures. Together with a large international team CWI senior researcher Léo Ducas contributed to two of these schemes: the public-key encryption scheme CRYSTALS-Kyber and the digital signature scheme CRYSTALS-Dilithium.

“The new schemes are absolutely necessary because the old ones are not secure against attacks with a quantum computer”, says Ducas. While a practical quantum computer is still under development, it is known that when adversaries will start to use it, today’s widely used digital security software can be broken.

Cryptographic schemes are always based on some extremely hard to crack mathematical problem. For decades the problem of factoring large numbers has been used in the so-called RSA-standard. CWI has a long track record in testing the security of RSA-based cryptographic standards. More recently elliptic curves have come to replace RSA, but they are not safe either for attacks by quantum computers.

Three out of the four so-called post-quantum cryptographic schemes chosen by NIST are based on lattices, including the two schemes Ducas worked on. Lattices are geometric structures of points that can be connected by lines. In lattice-based cryptography the geometric structure is used both for encoding and for decoding messages in a precisely defined mathematical way. Ducas: “While lattices are easy to visualize and work with in two dimensions, some problems become very hard in a large number dimension, in the hundreds or thousands, and this is what we harness for secure cryptography.”

Secure but not too expensive

More in particular, Ducas helped to analyze the security of the new lattice-based schemes CRYSTALS-Kyber and CRYSTALS-Dilithium. Ducas: “The larger the lattice, the longer the length of the cryptographic key and the more difficult the scheme is to break. But the longer the key, the more expensive encryption and decryption become. My work has helped to determine the optimal key length that is secure enough but not too expensive.”

Over the next few years, NIST will develop practical formats for the selected post-quantum cryptographic standards, Ducas says, which can then be gradually rolled out in practice. “Various bigger companies and governments are already switching to the new standards. In the long run the new standards will get to every computer and to all digital services.”

What Ducas is doing in the domain of digital security, CWI senior researcher Pablo César and his colleagues at the Distributed and Interactive Systems (DIS) group are doing in the domain of multimedia standards. “We focus on standards for three-dimensional video and on standards for the quality experienced by users”, says César.

For quality of experience standards, CWI is working on multi-party video conferencing. César: “Which factors determine the user experience? How does latency affect a video conversation? What are thresholds for a good user experience? How can we evaluate protocols in a standardized manner? These are some of the questions that we try to answer. In recent years the results of our work have already been used by the International Telecommunication Union (ITU), a standardization body of the United Nations responsible for information and communication technologies.”

For some applications, such as remote medical consultation, virtual classrooms, virtual museum visits or videoconferencing, communication via three-dimensional video would be superior to the traditionally used two-dimensional video. But to make three-dimensional video communication work, many scientific problems must be solved: What information is absolutely necessary to transmit and what information can be omitted for practical reasons? How to ensure that video communication can take place in real time? How to support all kinds of configurations and cameras? How to guarantee a rich user experience?

“We created compression algorithms that make the amount of data that needs to be transmitted much smaller”, says Cesar. “This work has been used by MPEG, the Moving Picture Experts Group, to benchmark computer programs, also called codecs, from various technology companies for encoding and decoding data streams. Our compression algorithms were the starting point of the Point Cloud Compression technologies, VPCC and GPCC, that were ultimately chosen by MPEG as the standards for immersive media coding.”

Very influential

The work on multimedia standards has a long and successful history at CWI. For example, the work of Dick Bulterman and Steven Pemberton on multimedia standards has been very influential in the World Wide Web Consortium (W3C). “Contributing to the development of standards fits perfectly in CWI’s mission”, says Cesar. “We have no commercial interest and we can often work on a topic much longer than commercial institutions can.”

Author: Bennie Mols