Léo Perrin, a researcher in Cryptography at the Inria Paris centre, was recently awarded a Starting Grant by the European Research Council. He will spend the next five years developing the mathematical and algorithmic foundations of innovative methods used in cryptography as part of the Rescale project, addressing new challenges facing cybersecurity.
Issues with online security
From encrypted messages and transaction tools to access cards and QR codes, cryptographyis a hidden component of digital services and applications that we use every day, helping to keep sensitive information (such as military intelligence or banking details) and personal information (e.g. medical or social information) private, authenticated and safe. It also contributes to online security in a broader sense, and is central to the cybersecurity of businesses, local authorities and the civil service.
The work carried out by the Cosmiq project team at the Inria Paris centre and Léo Perrin, a young research fellow from the team, is focused on developing cryptography algorithms. Perrin has been awarded a prestigious and selective ERC Starting Grant for 2022. Starting Grants give young scientists (two to seven years after completing their PhD) the opportunity to build a research team to work on an original subject. As part of the Rescale project (an acronym which stands for “Reinventing Symmetric Cryptography for Arithmetization over Large fiEld”), Léo Perrin will spend the next five years fine-tuning a mathematical theory and next-generation cryptographic algorithms.
As Léo Perrin explains, “Cryptography is constantly changing, as a result of regular advances made in cryptanalysis(the methods used in an attempt to decipher coded messages) and the emergence of new technology, such as the quantum computer,which could potentially make security for certain encryption methods obsolete. The work carried out by Cosmiq, a mix of both basic and practical aspects of information privacy (cryptanalysis, algorithm design and IT implementation), involves developing methods combining security and performance, meeting new needs in cryptography”.
The majority of the team's researchers come from mathematics or IT backgrounds, and one area in which they specialise is “lightweight cryptography”. This involves implementing cryptography algorithms using the minimum amount of computational resources - in order, for example, to secure objects operating with little available energy, such as embedded sensors or computers.
A new approach to cryptography
“Lightweight cryptography is based on concepts from traditional computing, in which algorithms use logic gates and encode information using bits”, explains Léo Perrin. “We have had good results in this field, as demonstrated by the achievements of some of our algorithms, which have regularly been put through their paces atcompetitions organised by the NIST(during which cryptography methods are tested): one of the algorithms I helped to designreached the final.”
But there is a growing need for more complex protocols, where the “traditional” demands of cryptography (keeping information private, authenticated and safe) will not just apply to a single message, but to an entire operation.
“This might eventually be used with the algorithm for Parcoursup, for example, for which a ‘black box’ is currently used. This would involve certifying the result of an operation (the posting offered) by ensuring that it had been carried out properly, factoring in all of the necessary information but without revealing values, in order to keep information on candidates private
 Parcoursup is an application process designed by both the French Ministry of National Education and the French Ministry of Higher Education, Research and Innovation to allocate undergraduate places to high school students and other candidates, mainly undergraduate students wanting a reorientation (https://en.wikipedia.org/wiki/Parcoursup)
A collective and individual scientific adventure
This requires a new type of cryptography, one in which the building blocks are no longer bits but rather abstract objects (“Galois groups”, mathematical units with rules for calculation, such as addition or multiplication, with specific properties). From a scientific perspective, Rescale has its sights set on rethinking cryptographic algorithms in light of these new approaches, and developing a theoretical framework that will make it possible to showcase their capacities. The aim will also be to share these theoretical results with a broad scientific community and to develop calculation libraries that will allow these new methods to be implemented.
Given the scale of the task facing Léo Perrin, the money allocated to the Rescale project by the ERC - a million and a half euros over the next five years - will not go to waste! The young researcher, who was able to count on the support of his colleagues from Cosmiq when it came to putting together his application for the grant, will draw on the skill sets of three PhD students and two postdocs.“In terms of the direction the research will take, ourearly results have been quite promising, and we will be able to explore the subject in greater detail over the next few years”, explains Léo Perrin. Aside from the individual achievement of being awarded an ERC Starting Grant, this brilliant young researcher is carrying a whole team along with him, the aim being to invent the next generation of cryptography.
A brief bio
Léo Perrin first became interested in cryptography while studying at the École Centrale de Lyon. Torn between specialising in mechanics or applied mathematics, he eventually opted for the latter out of an intellectual affinity with algebra and discrete sets. He also got a degree from the KTH Royal Institute of Technology in Sweden as part of an agreement between the two schools. In 2014 he spent a Master’s internship dealing with the theoretical side of cryptography at Aalto University in Finland. In 2017 he graduated with a PhD from the University of Luxembourg, researching attack and defence algorithms in symmetric cryptography.
This helped to launch his career as a researcher. After spending a few months at the Ruhr University Bochum in Germany and the University of Copenhagen in Denmark, he completed two postdoctorates as a member of the Secret team at Inria Paris. He notably invented a method for analysing algorithms, updating the hidden structure in the latest Russian crypto standards. Having joined Inria in 2019 as a research fellow, his work has included exploring new algorithms in symmetric cryptography, as well as more fundamental problems in discrete mathematics.
The Cosmiq project team in brief
The bulk of the research carried out by the project team Cosmiq, a successor to the project teams Code and Secret, concerns designing and analysing security for cryptographic algorithms, whether in traditional or quantum computing. Academic in nature, this covers both theoretical (the framework and the mathematical properties of algorithms) and applied aspects (algorithm design and implementation).