Latest Past Seminars

Symbolic protocol verification with dice: process equivalences in the presence of probabilities

Abstract: Symbolic protocol verification generally abstracts probabilities away, considering computations that succeed only with negligible probability, such as guessing random numbers or breaking an encryption scheme, as impossible. This abstraction, sometimes referred to as the perfect cryptography assumption, has shown very useful as it simplifies automation of the analysis. However, probabilities may also appear in the control flow where they are generally not negligible. In this paper we consider a framework for symbolic protocol analysis with a probabilistic choice operator: the probabilistic applied pi calculus. We define and explore the relationships between several behavioral equivalences. In particular we show the need for randomized schedulers and exhibit a counter-example to a result in a previous work that relied on non-randomized ones. As in other frameworks that mix both non-deterministic and probabilistic choices, schedulers may sometimes be unrealistically powerful. We therefore consider two subclasses of processes that avoid this problem. In particular,…

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Not so AdHoc testing: formal methods in the standardization of the EDHOC protocol

Abstract: We believe that formal methods in security should be leveraged in all the standardisation's of security protocols in order to strengthen their guarantees. To be effective, such analyses should be:
* maintainable: the security analysis should be performed on every step of the way, i.e. each iteration of the draft;
* pessimistic: all possible threat models, notably all sort of compromise should be considered;
* precise: the analysis should notably include as many real life weaknesses of the concrete cryptographic primitives specified.

In this talk, we illustrate how such a goal may be approached by detailing our analysis of the current IETF draft standard of the EDHOC protocol, as well as our subsequent interactions with its LAKE working group.
We will proceed in three steps, first introducing the Sapic+ platform that allows from a single modeling of a protocol to benefit from all the capabilities of multiple automated verification tools (ProVerif,Tamarin,DeepSec). We will then introduce multiple recent advances on how to better model the cryptographic primitives and their real life weaknesses. We will finally show how we leveraged Sapic+ along with the advanced primitive models to analyze the EDHOC protocol and provide feedback to the LAKE working group that has been integrated in latter drafts.

A little more conversation, a little less action, a lot more satisfaction: Global states in ProVerif

ProVerif is a popular tool for the fully automatic analysis of security protocols, offering very good support to detect flaws or prove security. One exception is the case of protocols with global states such as counters, tables, or more generally, memory cells. ProVerif fails to analyse such protocols, due to its internal abstraction.

In the original paper of GSVerif, our key idea was to devise a generic transformation of the security properties queried to ProVerif. We proved the soundness of our transformation and implemented it into a front-end GSVerif. Our experiments showed that our front-end (combined with ProVerif) outperforms the few existing tools, both in terms of efficiency and protocol coverage. We successfully applied our tool to a dozen of protocols of the literature, yielding the first fully automatic proof of a security API and a payment protocol of the literature.

In the newest version of ProVerif, the generic transformations of GSVerif can be fully described in term of axioms, thus taking advantage of this new ProVerif feature.