3.2.1 Generic proof techniques

Most automated tools for verifying security properties rely on techniques stemming from automated deduction. Often existing techniques do however not apply directly, or do not scale up due to state explosion problems. For instance, the use of Horn clause resolution techniques requires dedicated resolution methods 3335. Another example is unification modulo equational theory, which is a key technique in several tools, e.g. 42. Security protocols however require to consider particular equational theories that are not naturally studied in classical automated reasoning. Sometimes, even new concepts have been introduced. One example is the finite variant property 37, which is used in several tools, e.g., Akiss  35, Maude-NPA 42 and TAMARIN  46. Another example is the notion of asymmetric unification 41 which is a variant of unification used in Maude-NPA to perform important syntactic pruning techniques of the search space, even when reasoning modulo an equational theory. For each of these topics we need to design efficient decision procedures for a variety of equational theories.

3.2.2 Dedicated procedures and tools

We design dedicated techniques for automated protocol verification. While existing techniques for security protocol verification are efficient and have reached maturity for verification of confidentiality and authentication properties (or more generally safety properties), our goal is to go beyond these properties and the standard attacker models, verifying the properties and attacker models identified in Section 3.1. This includes techniques that:

• can analyse indistinguishability properties, including for instance anonymity and unlinkability properties, but also properties stated in simulation-based (also known as universally composable) frameworks, which express the security of a protocol as an ideal (correct by design) system;
• take into account protocols that rely on a notion of mutable global state which does not arise in traditional protocols, but is essential when verifying tamper-resistant hardware devices, e.g., the RSA PKCS#11 standard, IBM's CCA and the trusted platform module (TPM);
• consider attacker models for protocols relying on weak secrets that need to be copied or remembered by a human, such as multi-factor authentication.

These goals are beyond the scope of most current analysis tools and require both theoretical advances in the area of verification, as well as the design of new efficient verification tools.

3.3.1 General design techniques

Design techniques include composition results that allow one to design protocols in a modular way 38, 36. Composition results come in many flavours: they may allow one to compose protocols with different objectives, e.g. compose a key exchange protocol with a protocol that requires a shared key or rely on a protocol for secure channel establishment, compose different protocols in parallel that may re-use some key material, or compose different sessions of the same protocol.

Another area where composition is of particular importance is Service Oriented Computing, where an “orchestrator” must combine some available component services, while guaranteeing some security properties. In this context, we work on the automated synthesis of the orchestrator or monitors for enforcing the security goals. These problems require the study of new classes of automata that communicate with structured messages.

3.3.2 New protocol design

We also design new protocols. Application areas that seem of particular importance are:

• External hardware devices such as security APIs that allow for flexible key management, including key revocation, and their integration in security protocols. The security fiasco of the PKCS#11 standard 34, 40 witnesses the need for new protocols in this area.
• Election systems that provide strong security guarantees. We have been working (in collaboration with the Caramba team) on a prototype implementation of an e-voting system, Belenios.
• Mechanisms for publishing personal information (e.g. on social networks) in a controlled way.

6.1.1 Belenios

• Name:
  Belenios - Verifiable online voting system
• Keyword:
  E-voting
• Functional Description:

  Belenios is an open-source online voting system that provides vote confidentiality and verifiability. End-to-end verifiability relies on the fact that the ballot box is public (voters can check that their ballots have been received) and on the fact that the tally is publicly verifiable (anyone can recount the votes). Vote confidentiality relies on the encryption of the votes and the distribution of the decryption key (no one detains the secret key).

  Belenios supports various kind of elections. In the standard mode, Belenios supports simple elections where voters simply select one or more candidates. It also supports arbitrary counting functions at the cost of a slightly more complex tally procedure for the authorities. For example, Belenios supports Condorcet, STV, and Majority Judgement, where voters order candidates and grade them.

  Belenios is available in several languages for the voters as well as the administrators of an election. More languages can be freely added by users.

• News of the Year:

  In 2021, our platform was used for the organization of about 2000 elections, with about 70,000 ballots counted.

  This year, we modified the voting platform to make it more user-friendly and responsive: it automatically adapts on a cell phone, for example. We also developed two new interfaces to vote by ranking the candidates (Condorcet) or by rating them (majority judgment). Following several requests, Belenios now offers weighted votes, where each voter has a certain number of votes. Less visible to users, an important change was the update of the cryptographic core, in order to better link a ballot to the context of the election. Finally, we initiated the development of a REST API and modernized the management of administrator accounts.

• URL:
  https://­www.­belenios.­org/
• Contact:
  Stéphane Glondu
• Participants:
  Pierrick Gaudry, Stéphane Glondu, Véronique Cortier
• Partners:
  CNRS, Inria

6.1.2 Tamarin

• Name:
  Tamarin prover
• Keywords:
  Security, Verification
• Functional Description:
  The Tamarin prover is a security protocol verification tool that supports both falsification and unbounded verification of security protocols specified as multiset rewriting systems with respect to (temporal) first-order properties and a message theory that models Diffie-Hellman exponentiation, bilinear pairing, multisets, and exclusive-or (XOR), combined with a user-defined convergent rewriting theory. Its main advantages are its ability to handle stateful protocols and its interactive proof mode. Moreover, it has been extended to verify equivalence properties. The tool is developed jointly by the PESTO team, the Institute of Information Security at ETH Zurich, and CISPA. In a joint effort, the partners wrote and published a user manual in 2016, available from the Tamarin website.
• News of the Year:
  One major strength of Tamarin is that it offers an interactive mode, allowing to go beyond what pushbutton tools can typically handle. Tamarin is for example able to verify complex protocols such as TLS or the authentication protocols from the 5G standard. However, one of its drawback is its lack of automation. For many simple protocols, the user often needs to help Tamarin by writing specific lemmas, called "sources lemmas", which requires some knowledge of the internal behaviour of the tool. Last year, Cortier and Dreier, in collaboration with Delaune, proposed a technique to automatically generate sources lemmas in Tamarin. They proved formally that the lemmas indeed hold, for arbitrary protocols that make use of cryptographic primitives that can be modelled with a subterm convergent equational theory (modulo associativity and commutativity). They have implemented their approach within Tamarin. Experiments show that, in most examples of the literature, suitable sources lemmas can now be automatically generated, in replacement of the handwritten lemmas. As a direct application, many simple protocols can now be analysed fully automatically, while they previously required user interaction. This year the same authors, together with Klein, improved their previous technique so that now sources lemmas can be generated in even further cases.
• URL:
  http://­tamarin-prover.­github.­io/
• Publications:
  hal-02991286, hal-02358878
• Contact:
  Jannik Dreier
• Participants:
  Jannik Dreier, Elise Klein, Maiwenn Racouchot, Véronique Cortier
• Partner:
  CISPA Helmholtz Center for Information Security

6.1.3 ProVerif

• Keywords:
  Security, Verification, Cryptographic protocol
• Functional Description:

  ProVerif is an automatic security protocol verifier in the symbolic model (so called Dolev-Yao model). In this model, cryptographic primitives are considered as black boxes. This protocol verifier is based on an abstract representation of the protocol by Horn clauses. Its main features are:

  It can verify various security properties (secrecy, authentication, process equivalences).

  It can handle many different cryptographic primitives, specified as rewrite rules or as equations.

  It can handle an unbounded number of sessions of the protocol (even in parallel) and an unbounded message space.

• News of the Year:
  Vincent Cheval and Bruno Blanchet finished their work on several extensions of ProVerif: 1) support for integer counters, with incrementation and inequality tests, 2) lemmas and axioms to give intermediate results to ProVerif, which it exploits to help proving subsequent queries, by deriving additional information in the Horn clauses that it uses to perform the proofs, 3) proofs by induction on the length of the trace, by giving as lemma the property to prove, but obviously for strictly shorter traces, 4) temporal queries, which allow to order events. The soundness of these features is proved (by hand). Moreover, they optimized many algorithms used in ProVerif (generation of clauses, resolution, subsumption ...) resulting in impressive speedups on large examples. These features are included in ProVerif 2.02pl1 and a paper by Bruno Blanchet, Vincent Cheval, and Véronique Cortier has been published at Security and Privacy 2022.
• URL:
  http://­proverif.­inria.­fr/
• Publications:
  hal-03366962, hal-01947972, hal-01423742, hal-01306440, hal-01423760, hal-01102136, hal-01575920, hal-01528752, hal-01575923, hal-01527671, hal-01575861
• Contact:
  Bruno Blanchet
• Participants:
  Bruno Blanchet, Marc Sylvestre, Vincent Cheval

6.1.4 Jasmin

• Name:
  Jasmin compiler and analyser
• Keywords:
  Cryptography, Static analysis, Compilers
• Functional Description:

  The Jasmin programming language smoothly combines high-level and low-level constructs, so as to support “assembly in the head” programming. Programmers can control many low-level details that are performance-critical: instruction selection and scheduling, what registers to spill and when, etc. The language also features high-level abstractions (variables, functions, arrays, loops, etc.) to structure the source code and make it more amenable to formal verification. The Jasmin compiler produces predictable assembly and ensures that the use of high-level abstractions incurs no run-time penalty.

  The semantics is formally defined to allow rigorous reasoning about program behaviors. The compiler is formally verified for correctness (the proof is machine-checked by the Coq proof assistant). This justifies that many properties can be proved on a source program and still apply to the corresponding assembly program: safety, termination, functional correctness…

  Jasmin programs can be automatically checked for safety and termination (using a trusted static analyzer). The Jasmin workbench leverages the EasyCrypt toolset for formal verification. Jasmin programs can be extracted to corresponding EasyCrypt programs to prove functional correctness, cryptographic security, or security against side-channel attacks (constant-time).

• News of the Year:

  Year 2021 has brought several improvements to the Jasmin programming language, enabling the implementation of more complex programs: local functions (preserved during compilation), sub-arrays, etc. The release of a new major version is scheduled for early 2022.

  Preparatory works to the support of several target architectures have also been carried.

  The correctness theorem of the compiler has been made more precise. It now allows to reason at source level about some non-functional properties of the program produced by the compiler. In particular, there is now a formal proof (in Coq) that the compiler always preserves the “constant-time” security property.

• URL:
  https://­github.­com/­jasmin-lang/­jasmin
• Publications:
  hal-03430789, hal-02974993, hal-01649140
• Contact:
  Benjamin Grégoire
• Participants:
  Gilles Barthe, Benjamin Grégoire, Adrien Koutsos, Vincent Laporte, Jean-Christophe Lechenet, Swarn Priya

7.1.1 Foundations of Automated Verification: Semantics, Decidability and Complexity

Participants: Véronique Cortier, Steve Kremer, Raphaëlle Crubillé, Christophe Ringeissen.

Security properties of cryptographic protocols are typically expressed as reachability or equivalence properties. Secrecy and authentication are examples of reachability properties while privacy properties such as untraceability, vote secrecy, or anonymity are generally expressed as behavioral equivalence in a process algebra that models security protocols.

Cortier, Delaune and Sundararajan 9 identify a new decidable class of security protocols, both for reachability and equivalence properties. The result holds for an unbounded number of sessions and for protocols with nonces. It covers all standard cryptographic primitives. The class sets up three main assumptions. (i) Protocols need to be without else branch and “simple”, meaning that an attacker can precisely identify from which participant and which session a message originates from. (ii) Protocols should be type-compliant which is intuitively guaranteed as soon as two encrypted messages of the protocol cannot be confused. (iii) Finally, the dependency graph of the protocol must be acyclic. The dependency graph is a new notion that characterises how actions depend on each other. Revisiting this approach, Cortier, Dallon, and Delaune 17 show that it is possible to significantly bound the number of sessions for a similar class of protocols, for both reachability and equivalence properties. Experiments show that on most basic protocols of the literature, the proposed algorithm computes a small number of sessions (a dozen). As a consequence, tools for a bounded number of sessions like DeepSec can then be used to conclude that a protocol is secure for an unbounded number of sessions.

Cheval (Inria Paris), Crubillé and Kremer study probabilistic process equivalences for security protocols. Symbolic models are classically purely non-deterministic. Indeed, generating random keys and nonces, or using randomized cryptographic primitives (like any secure encryption scheme) is idealized in symbolic models, replacing random numbers that can be guessed with only a negligeable probability with perfectly fresh values that cannot be guessed at all. This abstraction has been widely used and has shown its usefulness. Another source of randomness may however come from the control flow. Typically, protocols aiming at anonymity, such as the Dining Cryptographers protocol, require users to take one action or another probabilistically. In this work we propose an extension of the applied pi calculus with a probabilistic choice operator (${+}_p$) and corresponding process equivalences. We show that it is essential that schedulers in such a probabilistic calculus are randomized, as non-randomized schedulers lead to definitions that have undesirable properties. We for instance show that typical behavioral relations would not be transitive and point out a flaw in the main theorem of a previous framework  44 that chose non-randomized schedulers. Mixing non-determinism and probabilistic choices generally leads to unsatisfactory behavioral equivalences: as the non-deterministic choices can leak the probabilistic choices, the resulting equivalences is too strong, modelling unrealistic attacker capabilities. We therefore investigate two sub-classes of protocols. We first consider the class of protocols that do not make any probabilistic choices, but allow the attacker to do so. Even though the honest processes may be purely non-deterministic, the resulting may testing equivalence is strictly stronger by allowing a probabilistic attacker. We show that for a bounded number of sessions may-testing with a probabilistic attacker coincides with purely possibilistic similarity. Second, we consider a class of simple processes, with a very limited non-determinism. For this class, we show that trace equivalence coincides with may-testing where attackers are sequential processes (no parallel, nor non-deterministic choice).

In collaboration with Erbatur (UT Dallas, USA) and Marshall (Univ Mary Washington, USA), Ringeissen studies decision procedures for equational theories used in protocol analysis. In 19, 29 hierarchical unification procedures have been developed for non-disjoint unions of theories closed by equational paramodulation such as paramodulation modulo Associativity-Commutativity. Beyond the decision problems related to equational unification and (intruder) theories, Ringeissen is also working on SMT (Satisfiability Modulo Theories) solvers to model verification conditions. In collaboration with Sheng, Zohar, Lange, Barrett (Stanford, USA) and Fontaine (Veridis project-team and University of Liège, Belgium), Ringeissen has published a new short paper showing that the theory of datatypes is strongly polite and so it can be combined with arbitrary disjoint theories to get a satisfiability procedure using polite combination 21. In collaboration with Sheng, Zohar, Barrett (Stanford, USA) together with Reynolds and Tinelli (U. Iowa, USA), Ringeissen has been involved into a new contribution to the study of polite combination. In 22, the difference between polite and strongly polite theories has been proven and an optimization is proposed to the polite combination method. This optimization allows us to reduce the number of guessings to be considered, in a way similar to the Nelson-Oppen method. Preliminary evidence is shown for this by demonstrating a speed-up on a smart contract verification benchmark.

7.1.2 Improving Verification Tools

Participants: Véronique Cortier, Jannik Dreier, Lucca Hirschi, Elise Klein, Steve Kremer.

7.1.3 Analysis of Deployed Protocols

Participants: Jannik Dreier, Lucca Hirschi, Steve Kremer, Vincent Laporte.

7.1.4 Symbolic Methods in Computational Cryptography Proofs

Participants: Steve Kremer.

In a paper published in ACM TOCL 8, Barthe (MPI Security and Privacy), Jacomme (CISPA) and Kremer study decidability problems for equivalence of probabilistic programs, for a core probabilistic programming language over finite fields of fixed characteristic. The programming language supports uniform sampling, addition, multiplication and conditionals and thus is sufficiently expressive to encode boolean and arithmetic circuits. We consider two variants of equivalence: the first one considers an interpretation over the finite field ${𝔽}_q$, while the second one, which we call universal equivalence, verifies equivalence over all extensions ${𝔽}_{q^k}$ of ${𝔽}_q$. The universal variant typically arises in provable cryptography when one wishes to prove equivalence for any length of bitstrings, i.e., elements of ${𝔽}_{2^k}$ for any $k$. While the first problem is obviously decidable, we establish its exact complexity which lies in the counting hierarchy. To show decidability, and a doubly exponential upper bound, of the universal variant we rely on results from algorithmic number theory and the possibility to compare local zeta functions associated to given polynomials. We then devise a general way to draw links between the universal probabilistic problems and widely studied problems on linear recurrence sequences. Finally we study several variants of the equivalence problem, including a problem we call majority, motivated by differential privacy. We also define and provide some insights about program indistinguishability, proving that it is decidable for programs always returning 0 or 1.

7.1.5 Symbolic Model Guided Fuzzing of Cryptographic Protocols

Participants: Max Ammann, Lucca Hirschi, Steve Kremer.

Fuzzing implementations of cryptographic protocols is challenging. In contrast to traditional fuzzing of file formats, cryptographic protocols require a specific flow of cryptographic and mutually dependent messages to reach deep protocol states. Moreover, the state-of-the-art fuzzing techniques are adequate to find safety vulnerabilities (sometimes with potential security implications) but are unfortunately unable to find logical attacks in protocols, i.e., attacks that exploit protocol logic flaws. Indeed, most of these techniques generate random operations such as bit-flips on network packets, which make logical attack finding overwhelmingly unlikely, and use a code-based notion of coverage, which is a poor feedback as it falls short of capturing the diversity of executions corresponding to different adversarial behaviours that reach the same code coverage.

In his master thesis, Max Ammann has designed, implemented, and evaluated a new fuzzing engine tailored to capture logical attacks in cryptographic protocols and applied it to the TLS 1.2 and TLS 1.3 protocols. The core idea of this fuzzing engine is to consider the input space to be fuzzed to be symbolic traces in a Dolev-Yao-style model that are executed by target TLS libraries such as OpenSSL through concretizing of symbolic messages as bitstrings. Although the TLS specifications have been formally verified multiple times establishing strong security guarantees, those guarantees do not apply on the actual implementations that are in use. Because the development of cryptographic protocols is error-prone, multiple security vulnerabilities have already been discovered in implementations in TLS which are not present in its specification. The goal of this fuzzing methodology is to explore this blind spot in between formal verification and testing.

Inspired by symbolic protocol verification, the thesis presents a reference implementation of a fuzzer named TLSPuffin which employs a concrete semantic to execute TLS 1.2 and 1.3 symbolic traces. This method allows us to utilise a genetic fuzzing algorithm to fuzz protocol flows. The novel approach allows rediscovering known vulnerabilities in TLS, which are out-of-scope for classical bit-level fuzzers.

7.1.6 Security of Cryptographic Implementations

Participants: Vincent Laporte.

7.1.7 Protocol Design

Participants: Jannik Dreier.

In 1968, Liu described the problem of securing documents in a shared secret project. In an example, at least six out of eleven participating scientists need to be present to open the lock securing the secret documents. Shamir proposed a mathematical solution to this physical problem in 1979, by designing an efficient $k$-out-of-$n$ secret sharing scheme based on Lagrange's interpolation. Liu and Shamir also claimed that the minimal solution using physical locks is clearly impractical and exponential in the number of participants.

In this work accepted for the Journal of Computer Security 10 Dreier, Dumas, Lafourcade, and Robert relax some implicit assumptions in Liu and Shamir's claim and propose an optimal physical solution to the problem of Liu that uses physical padlocks, but the number of padlocks is not greater than the number of participants. Then, we show that no device can do better for $k$-out-of-$n$ threshold padlock systems as soon as $k\ge \sqrt{2n}$, which holds true in particular for Liu's example. More generally, we derive bounds required to implement any threshold system and prove a lower bound of $Olog\left(n\right)$ padlocks for any threshold larger than 2. For instance we propose an optimal scheme reaching that bound for 2-out-of-$n$ threshold systems which requires less than $2{log}_2\left(n\right)$ padlocks. We also discuss more complex access structures, a wrapping technique, and other sublinear realizations like an algorithm to generate 3-out-of-$n$ systems with $2.5\sqrt{n}$ padlocks. Finally we give an algorithm building $k$-out-of-$n$ threshold padlock systems with only $Olog{\left(n\right)}^{k-1}$ padlocks. Apart from the physical world, our results also show that it is possible to implement secret sharing over small fields.

7.2.1 Design of E-Voting Protocols

Participants: Véronique Cortier, Alexandre Debant, Jannik Dreier, Mathieu Turuani, Quentin Yang.

As a part of a contract with Idemia, Cortier, Debant, Dreier, Turuani and Yang are designing a novel electronic voting system, tailored to the voting context envisioned by Idemia. The system is made for on-site elections, with the use of smart cards. However, the goal is that the trust should not be placed in one single part of the system, hence smart cards can not be trusted. One originality of the approach is the possibility to re-use existing techniques, in conjunction with the use of smart-cards and paper ballots. The designed protocol is meant to achieve vote secrecy, coercion resistance, and cast as intended. Coercion resistance is eased by the fact that voters enter a physical voting booth. Cast-as-intended was more difficult to achieve since Idemia aimed at two strong guarantees: all cast ballots should be audited by voters (this is not an option left to the choice of the voter) and whenever the system attempts to cheat, its misbehavior can be proved to a third party, possibly yielding to a punishment of the system. The proposed protocol has been proved secure with the ProVerif tool using some of its new features as explained in Section 7.1.2. A challenge was to cover three families of properties (vote secrecy, verifiability, and accountability) under various corruption scenarios, in a unified way.

There are two main approaches for tallying an election in the context of electronic voting. The first one is the homomorphic tally. Thanks to the homomorphic property of the encryption scheme (typically ElGamal), the ballots are combined to compute the (encrypted) sum of the votes. Then only the resulting ciphertext needs to be decrypted to reveal the election result, without leaking the individual votes. However, it can only be applied to simple vote counting functions. The second main approach is based on mixnets. The encrypted ballots are shuffled and re-randomized such that the resulting ballots cannot be linked to the original ones. Several mixers are successively used and then each (randomized) ballot is decrypted, yielding the original votes in clear, in a random order. It can be used for any vote counting function but it reveals much more information than the result itself (the winner(s) of the election) and is subject to so-called Italian attacks. Quentin Yang, co-supervised by Cortier and Gaudry (Caramba project-team), has studied the possibility to compute the election result from a set of encrypted ballots, without leaking any other information. This can be seen as an instance of Multi-Party Computation (MPC). Cortier, Gaudry and Yang 27 have unveiled several flaws or limitations of the existing works and they have provided a toolbox to implement, at a reasonable cost, several key counting functions of the literature: Majority Judgement, Condorcet, and STV. One of the surprises of the work lies in the fact that they show that it is often preferable to use the very standard El Gamal encryption instead of Paillier encryption, that is typically considered as the Swiss-knife for MPC.

7.2.2 Security analyses of E-Voting Protocols

Participants: Véronique Cortier, Alexandre Debant, Lucca Hirschi.

7.3.1 Privacy Protection in Social Networks

Participants: Bizhan Alipour, Noreddine Belhadj-Cheikh, Abdessamad Imine, Michaël Rusinowitch.

Social media such as Facebook provide a new way to connect, interact and learn. Facebook allows users to share photos and express their feelings by using comments. However, Facebook users are vulnerable to attribute inference attacks where an attacker intends to guess private attributes (e.g., gender, age, political view) of target users through their online profiles and/or their vicinity (e.g., what their friends reveal). Given user-generated pictures on Facebook, Alipour, Imine and Rusinowitch show how to launch gender inference attacks on their owners from picture metadata composed of: (i) alt-texts generated by Facebook to describe the content of pictures, and (ii) comments posted by friends, friends of friends or regular users. They assume these two types of meta-data are the only available information to the attacker. Evaluation results demonstrate that an adversary can infer the gender with high accuracy by combining alt-texts and comments. Moreover they can identify sensitive words in the meta-data and hide them to decrease drastically the adversary's prediction accuracy. To our knowledge, this is the first inference attack on Facebook that exploits comments and alt-texts solely. Moreover by computing several vector representations for the same word or emoji, each one being specific to an attribute value, the machine algorithms can select the best one to boost the model accuracy 18. In our experiments, the attributes of Facebook users can be inferred from commenters’ reactions to their publications with an AUC from 94% to 98%, depending on the traits (gender, age, relationship status). Bizhan Alipour's thesis to be defended in February 2022 will present in more detail the employed techniques and the results. Protection against these attribute inference attacks has been investigated using machine learning explainability and adversarial defense strategies. More precisely, effective adversarial reactions have been generated to fool sensitive attribute (blackbox) classifiers 14. Experiments show that the resulting FOX system successfully fools (about 99.7% and 93.2% of the time) the classifiers, improving set-of-the-art baselines with a good transferability of adversarial features.

7.3.2 Privacy-Preserving Big Data Management

Participants: Abdessamad Imine, Ala Eddine Laouir.

Nowadays, big data management is gaining momentum within the research community. Basically, the main issue of supporting privacy-preserving big data management plays a first-class role, especially with respect to the wide class of emerging big data applications, such as social networks, bio-informatics and web recommendation systems. Co-supervised with Pr Alfredo Cuzzocrea (Excellence Chair in Computer Engineering, Lorraine University), the main objectives of Ala Eddine Laouir's thesis consist in devising new models and methods for effectively supporting privacy-preserving big data management in distributed environments, and providing significant realizations in reference case studies.

7.3.3 Efficient Management of Filtering Rules in Software-defined Networking

Participants: Ahmad Abboud, Michaël Rusinowitch.

In a joint project with the Resist project-team and the Numeryx company, Abboud, Lahmadi (Resist) and Rusinowitch are working on the design, implementation and evaluation of a double-mask technique for building compressed, verifiable filtering rules in Software Defined Networks. As an alternative solution to the memory limitation of switches they investigate the distribution of filtering rules among several devices while preserving the network policy semantics. They also apply the rules distribution algorithm to design an efficient update strategy for varying sets of rules and topologies 24.

9.1.1 Other european programs/initiatives

Participant: Steve Kremer.

• COST ACTION CA19122 EUGAIN — European Network For Gender Balance in Informatics, duration: 4 years, since 2020, participant and leader of Working Group 3 – From PhD to Professor: Steve Kremer

  Women are underrepresented in Informatics at all levels, from undergraduate and graduate studies to participation and leadership in academia and industry. The main aim and objective of EUGAIN is to improve gender balance in Informatics at all levels through the creation of a European network of colleagues working on the forefront of the efforts for gender balance in Informatics in their countries and research communities.

9.2.1 ANR

• ANR Chaire IA ASAP Tools for automated, symbolic analysis of real-world cryptographic protocols, duration: September 2020 – August 2024, leader: Steve Kremer.

  The goal of this project is the development of efficient algorithms and tools for automated verification of cryptographic protocols, that are able to comprehensively analyse detailed models of real-world protocols building on techniques from automated reasoning. Automated reasoning is the subfield of AI whose goal is the design of algorithms that enable computers to reason automatically, and these techniques underlie almost all modern verification tools. Current analysis tools for cryptographic protocols do however not scale well, or require to (over)simplify models, when applied on real-world, deployed cryptographic protocols. We aim at overcoming these limitations: we therefore design new, dedicated algorithms, include these algorithms in verification tools, and use the resulting tools for the security analyses of real-world cryptographic protocols.

• ANR TECAP Protocol Analysis — Combining Existing Tools, duration: January 2018 – June 2022, leader: Vincent Cheval, other partners: ENS Cachan, Inria Paris, Inria Sophia Antipolis, IRISA, LIX.

  Despite the large number of automated verification tools, several cryptographic protocols (e.g. stateful protocols) still represent a real challenge for these tools and reveal their limitations. To cope with these limits, each tool focuses on different classes of protocols depending on the primitives, the security properties, etc. Moreover, the tools cannot interact with each other as they evolve in their own model with specific assumptions. The aim of this project is to get the best of all these tools, that is, to improve the theory and implementation of each individual tool towards the strengths of the others and to build bridges that allow the cooperation of the methods/tools. We will focus in this project on CryptoVerif, EasyCrypt, Scary, ProVerif, TAMARIN, Akiss and APTE. In order to validate the results, we will apply them to several case studies such as the Authentication and Key Agreement protocol from the telecommunication networks, the Scytl and Helios voting protocols, and the low entropy 3D-Secure authentication protocol. These protocols have been chosen to cover many challenges that the current tools are facing.

• ANR SEVERITAS Secure and Verifiable Test and Assessment System, duration: Mai 2021 – April 2025, local coordinator: Jannik Dreier, other partners: LIG/University Grenoble Alpes (coordinator France), SnT/University of Luxembourg (coordinator Luxembourg), LIMOS/Université Clermont Auvergne.

  SEVERITAS advances information socio-technical security for Electronic Test and Assessment Systems (e-TAS). These systems measure skills and performances in education and training. They improve management, reduce time-to-assessment, reach larger audiences, but they do not always provide security by design. This project recognizes that the security aspects for e-TAS are still mostly unexplored. We fill these gaps by studying current and other to-be-defined security properties. We develop automated tools to advance the formal verification of security and show how to valide e-TAS security rigorously. We develop new secure, transparent, verifiable and lawful e-TAS procedures and protocols. We also deploy novel run-time monitoring strategies to reduce frauds and study the user experience about processes to foster e-TAS usable security. Thanks to connections with players in the business of e-TAS, such as OASYS, this project will contribute to the development of secure e-TAS.

10.1.1 Scientific events: selection

10.1.2 Journal

10.1.3 Invited talks

• Véronique Cortier. Invited talk at the Isaac Newton Institute workshop on Verified software: from theory to practice (virtual), May 2021.
• Véronique Cortier. Invited talk at Laboratoire Méthodes Formelles (LMF, Saclay), December 2021.
• Véronique Cortier. Invited talk at SnT - Interdisciplinary Centre for Security, Reliability and Trust, University of Luxembourg, November 2021.
• Jannik Dreier. Invited lecture at GDR Sécurité winter school (virtual), February 2021, France.
• Lucca Hirschi. Invited lecture at GDR IM summer school (virtual), July 2021, France.
• Lucca Hirschi. Invited lecture at GDR Sécurité winter school (virtual), February 2021, France.
• Steve Kremer. Invited talk at the Académie des Sciences, Mai 2021.
• Vincent Laporte. Invited talk at the Coq workshop (virtual), July 2021.

10.1.4 Leadership within the scientific community

• Véronique Cortier: vice-chair of ACM Special Interest Group on Logic and Computation (SigLog)
• Véronique Cortier: member of IFIP WG-1.7 Foundations of Security Analysis
• Véronique Cortier: member of the research council of ANSSI
• Jannik Dreier: Co-chair of the working group on formal methods for security (GT MFS) of the GdR Sécurité Informatique
• Steve Kremer: member of IFIP WG-1.7 Foundations of Security Analysis
• Steve Kremer: member of the scientific directorate of the International Computer Science Meeting Center Schloss Dagstuhl
• Michaël Rusinowitch: member of the IFIP WG-11.14 Secure Engineering
• Michaël Rusinowitch: member of the Skolem Award committee in 2021

10.1.5 Scientific expertise

• Véronique Cortier: member of the expert panel on Computer Science of the Research Foundation – Flanders (FWO)
• Véronique Cortier: external expertises for the Swiss National Science Foundation

10.1.6 Research administration

• Steve Kremer: co-chair of Inria's Committee on Gender Equality and Equal Opportunities

10.2.1 Teaching

• Licence:

  J. Dreier, Introduction to Logic, Fall 2021, 20 hours (ETD), TELECOM Nancy

  V. Laporte, Introduction to Theoretical Computer Science (Logic, Languages, Automata), Spring 2021, 42 hours (ETD), TELECOM Nancy

  V. Laporte, Introduction to Logic, Fall 2021, 20 hours (ETD), TELECOM Nancy

• Master:

  J. Dreier, Protocol Security and Verification, 39 hours (ETD), M2 Computer Science, TELECOM Nancy

  J. Dreier, Advanced Cryptography, 37 hours, M2 Computer Science, TELECOM Nancy

  A. Imine, Security for XML Documents, 12 hours (ETD), M1, Univ Lorraine

  S. Kremer, Security Theory, 24 hours (ETD), M2 Computer science, Univ Lorraine

  C. Ringeissen, Decision Procedures for Software Verification, 8 hours (ETD), M2 Computer science, Univ Lorraine

  L. Vigneron, Introduction to cryptography, 17 hours (ETD), Polytech Nancy – Information Systems and Networks, Univ Lorraine

  L. Vigneron, Advanced Security, 30 hours (ETD), Polytech Nancy – Information Systems and Networks, Univ Lorraine

  L. Vigneron, Security of information systems, 28 hours (ETD), M2 MIAGE – Audit and Design of Information Systems, Univ Lorraine

• Summer School:

  J. Dreier and L. Hirschi. Symbolic verification of cryptographic protocols using Tamarin. “Cyber In Saclay” French Cybersecurity Doctoral School on formal methods for security, virtual, February 2021.

  V. Laporte. Machine-Checked Cryptography with EasyCrypt and Jasmin, Summer School of the SAC 2021 conference (Selected Areas in Cryptography), virtual, October 2021.

10.2.2 Supervision

• PhD defended in 2021:

  Ahmad Abboud, Efficient Rules Management Algorithms In Software Defined Networking 24, December 9th 2021, Univ. Lorraine (Abdelkader Lahmadi and Michaël Rusinowitch)

  Itsaka Rakotonirina, Symbolic verification of cryptographic protocols: theory and practice 25, February 1st 2021, Univ. Lorraine (S. Kremer and V. Cheval).

• PhD in progress:

  Elise Klein, Automatic Synthesis of Cryptographic Protocols, started in October 2021. (J. Dreier and S. Kremer)

  Bizhan Alipour Pijani, Attribute Inference Attacks on Social Network Publications started in October 2018 (A. Imine and M. Rusinowitch)

  Maïwenn Racouchot, Automated Learning of Proof Strategies in Tamarin, started in October 2021. (J. Dreier and S. Kremer)

  Quentin Yang, Design of a cast-as-intended, verifiable, and coercion-resistant electronic voting protocol, started in November 2020. (V. Cortier and P. Gaudry)

10.2.3 Juries

10.3.1 Articles and contents

• V. Cortier has co-authored, with P. Gaudry (Caramba) a book on electronic voting, that will be published by Odile Jacob, in Spring 2022.

10.3.2 Interventions

• V. Cortier
  • interview on e-voting by various medias: Le Monde, Le Figaro, El Pais, France Info, Numerama, CNRS Le Journal
  • hearing at Commission Supérieure du Numérique et des Postes" (commission parlementaire bicamérale) on e-voting
  • invited talk at the CNIL (Commission Nationale Informatique et Libertés) on e-voting
  • hearing by a think tank of La République En Marche, on e-voting
  • “How to explain security protocols to your children” 23, 12 pages article written with Itsaka Rakotonirina, in Essays Dedicated to Joshua Guttman on the Occasion of his 66.66th Birthday, LNCS, Springer.
• S. Kremer
  • Interview on e-voting for a documentary by LCP (La Chaine Parlementaire).

International journals

• 8 articleG.Gilles Barthe, C.Charlie Jacomme and S.Steve Kremer. Universal Equivalence and Majority of Probabilistic Programs over Finite Fields.ACM Transactions on Computational Logic231January 2022, 1-42
  HALDOIback to text
• 9 articleV.Véronique Cortier, S.Stéphanie Delaune and V.Vaishnavi Sundararajan. A decidable class of security protocols for both reachability and equivalence properties.Journal of Automated Reasoning652021
  HALDOIback to text
• 10 articleJ.Jannik Dreier, J.-G.Jean-Guillaume Dumas, P.Pascal Lafourcade and L.Léo Robert. Optimal Threshold Padlock Systems.Journal of Computer Security2021, 1-34
  HALDOIback to text
• 11 articleC.Charlie Jacomme and S.Steve Kremer. An Extensive Formal Analysis of Multi-factor Authentication Protocols.ACM Transactions on Privacy and Security242February 2021, 1-34
  HALDOIback to text

International peer-reviewed conferences

• 12 inproceedingsG.Gilles Barthe, B.Benjamin Grégoire, V.Vincent Laporte and S.Swarn Priya. Structured Leakage and Applications to Cryptographic Constant-Time and Cost.CCS '21: 2021 ACM SIGSAC Conference on Computer and Communications SecurityCCS '21: Proceedings of the 2021 ACM SIGSAC Conference on Computer and Communications SecurityVirtual Event, South KoreaACMNovember 2021, 462-476
  HALDOIback to text
• 13 inproceedingsD.David Basin, J.Jannik Dreier, S.Sofia Giampietro and S.Saša Radomirović. Verifying Table-Based Elections.CCS '21: 2021 ACM SIGSAC Conference on Computer and Communications SecurityCCS '21: Proceedings of the 2021 ACM SIGSAC Conference on Computer and Communications SecurityVirtual Event, South KoreaACMNovember 2021, 2632-2652
  HALDOIback to text
• 14 inproceedingsN.Noreddine Belhadj-Cheikh, A.Abdessamad Imine and M.Michaël Rusinowitch. FOX: Fooling with Explanations Privacy Protection with Adversarial Reactions in Social Media.18th Annual International Conference on Privacy, Security and Trust (PST2021)Auckland/Virtual, New ZealandDecember 2021
  HALback to text
• 15 inproceedingsB.Bruno Blanchet, V.Vincent Cheval and V.Véronique Cortier. ProVerif with Lemmas, Induction, Fast Subsumption, and Much More.43RD IEEE Symposium on Security and Privacy (S&P'22)San Francisco, United StatesMay 2022
  HALback to text
• 16 inproceedingsY.Yannick Chevalier and M.Michaël Rusinowitch. Implementing Security Protocol Monitors.Proceedings SCSS 20219th International Symposium on Symbolic Computation in Software Science (SCSS 2021)342Linz/virtual, AustriaSeptember 2021, 22-34
  HALDOI
• 17 inproceedingsV.Véronique Cortier, A.Antoine Dallon and S.Stéphanie Delaune. A small bound on the number of sessions for security protocols.35th IEEE Computer Security Foundations Symposium- CSF 2022Haifa, IsraelAugust 2022
  HALback to text
• 18 inproceedingsS.Sanaz Eidizadehakhcheloo, B. A.Bizhan Alipour Pijani, A.Abdessamad Imine and M.Michaël Rusinowitch. Divide-and-Learn: A Random Indexing Approach to Attribute Inference Attacks in Online Social Networks.Data and Applications Security and Privacy XXXV - 35th Annual IFIP WG 11.3 Conference, DBSec 2021Calgary, CanadaJuly 2021
  HALback to text
• 19 inproceedingsS.Serdar Erbatur, A.Andrew Marshall and C.Christophe Ringeissen. Non-disjoint Combined Unification and Closure by Equational Paramodulation.Frontiers of Combining Systems - 13th International Symposium, FroCoS 202112941Lecture Notes in Computer ScienceBirmingham, United KingdomSpringerSeptember 2021, 25-42
  HALDOIback to text
• 20 inproceedingsL.Lucca Hirschi, L.Lara Schmid and D.David Basin. Fixing the Achilles Heel of E-Voting: The Bulletin Board.IEEE 34th Computer Security Foundations Symposium (CSF)Dubrovnik/Virtual, CroatiaIEEEJune 2021, 1-17
  HALDOIback to text
• 21 inproceedingsY.Ying Sheng, Y.Yoni Zohar, C.Christophe Ringeissen, J.Jane Lange, P.Pascal Fontaine and C.Clark Barrett. Politeness for the Theory of Algebraic Datatypes (Extended Abstract).Thirtieth International Joint Conference on Artificial Intelligence, IJCAI-21Proceedings of the Thirtieth International Joint Conference on Artificial Intelligence, Sister Conferences Best PapersMontreal, CanadaInternational Joint Conferences on Artificial Intelligence OrganizationAugust 2021, 4829-4833
  HALDOIback to text
• 22 inproceedingsY.Ying Sheng, Y.Yoni Zohar, C.Christophe Ringeissen, A.Andrew Reynolds, C.Clark Barrett and C.Cesare Tinelli. Politeness and Stable Infiniteness: Stronger Together.28th International Conference on Automated Deduction, CADE 2812699Lecture Notes in Computer SciencePittsburgh, United StatesSpringerJuly 2021, 148-165
  HALDOIback to text

Scientific book chapters

• 23 inbookV.Véronique Cortier and I.Itsaka Rakotonirina. How to explain security protocols to your children.13066Protocols, Strands, and Logic -Essays Dedicated to Joshua Guttman on the Occasion of his 66.66th BirthdayLNCSSpringer2021, 112-123
  HALDOIback to text

Doctoral dissertations and habilitation theses

• 24 thesisA.Ahmad Abboud. Efficient Rules Management Algorithms in Software Defined Networking.University of LorraineDecember 2021
  HALback to textback to text
• 25 thesisI.Itsaka Rakotonirina. Efficient verification of observational equivalences of cryptographic processes : theory and practice.Université de LorraineFebruary 2021
  HALback to text

Reports & preprints

• 26 reportV.Véronique Cortier, A.Alexandre Debant and P.Pierrick Gaudry. A privacy attack on the Swiss Post e-voting system.Université de Lorraine, CNRS, Inria, LORIANovember 2021
  HALback to text
• 27 miscV.Véronique Cortier, P.Pierrick Gaudry and Q.Quentin Yang. A toolbox for verifiable tally-hiding e-voting systems.April 2021
  HALback to text
• 28 miscJ.Jannik Dreier, J.-G.Jean-Guillaume Dumas, P.Pascal Lafourcade and L.Léo Robert. Optimal Threshold Padlock Systems.March 2021
  HAL
• 29 miscS.Serdar Erbatur, A. M.Andrew M Marshall and C.Christophe Ringeissen. Non-disjoint Combined Unification and Closure by Equational Paramodulation (Extended Version).2021
  HALDOIback to text
• 30 reportI.Idmhand Fatiha, I.Ioana Galleron, A. E.Ala Eddine Laouir, A.Andres Echavarria and L.Laurent Passion. FAIRiser vos données : mémorandum.CAHIER - Consortium CAHIEROctober 2021
  HAL

Scientific popularization

• 31 articleI.Itsaka Rakotonirina. Les livraisons dangereuses.IntersticesJanuary 2021
  HAL