Thèse de Matthieu Bettinger

Sujet :
Blockchain Interoperability/composability

Date de début : 01/11/2021
Date de fin (estimée) : 01/11/2024

Encadrant : Sonia Ben Mokhtar
Co-encadrant : Lionel Brunie

Résumé :

Blockchain is a truly disruptive paradigm that is impacting the way applications are designed in

virtually every domain, from voting to insurance, banking and identity management, through mobility,

healthcare and education. By removing the need for any trusted party, blockchains provide developers

with trust assumptions that are radically different from the ones of traditional applications.

While blockchains and decentralization technologies foreshadow the cornerstone infrastructure for the

future economy, they gain both in functionality and in complexity. Initially developed for

cryptocurrencies, blockchains now have strong requirements for scalability and privacy brought by

their industrial usage. This has led to the development of a variety of novel Blockchain technologies.

However, the field reality is that the heterogeneity of current blockchain implementations, the fast pace

of their development, and the critical nature of decentralized applications keep blockchains out of the

reach of most practitioners. Indeed, blockchain frameworks such as Ethereum and Hyperledger come

in many different flavors of consensus algorithms (Proof-of-Work, Proof-of-Authority, BFT protocols

etc.), of cryptographic techniques (Zero-Knowledge proofs, MPC, etc.) and of membership management

(public vs permissioned).

These blockchain flavors, such as the Enterprise Ethereum Alliance (EEA) projects (e.g., Parity,

Quorum) typically address a single use case, meaning that they are available off-the-shelf, but

monolithic. This situation creates a true gap between practitioners’ constraints and the projects that

are readily available. Therefore, practitioners tend to either take off-the-shelf (relatively stable)

blockchain implementations (e.g., Bitcoin, Ethereum, Hyperledger Fabric) despite their possible

inadequacy with respect to their own needs, or (for the more adventurous ones) launch expensive, time

consuming and often unsuccessful developments for designing their own blockchain.

The main objective of this PhD thesis is to investigate novel solutions for Blockchain composition. To

reach this objective the PhD student shall follow the following phases:

1. Blockchain characterisation: the first challenge that will be addressed in this PhD thesis lies in

a thorough investigation of modern/popular blockchains (e.g., blockchains under the

Hyperledger consortium of the Linux foundation) both theoretically (e.g., extracting their

underlying security/dependability assumptions/properties) and practically (e.g., by assessing

their effective performance in the wild using well-defined benchmarks).

2. Blockchain interoperability: one major issue when it comes to composing existing blockchains

is their heterogeneity and hence their incapacity to interoperate. In this phase, the PhD student


will investigate blockchain interoperability mechanisms, assess the effectiveness and limitations

of existing solutions and propose novel bridging techniques.

3. Blockchain composition: in this phase, the PhD student will identify compatible and

incompatible blockchains from a functional perspective, and the impact of their composition on

the non-functional properties (e.g., security properties do not necessarily sum up when

composing two blockchains). He will further investigate semi-automatic composition

mechanisms from a specification of functional and non-functional properties and by relying on

the bridging techniques devised in step 2