Blockchain à faible empreinte énergétique adaptée au domaine financier

Abstract

Blockchain technology, and more broadly distributed ledger systems, hold the promise of transforming financial infrastructures by enabling more transparent, auditable, and tamper-resistant systems. It is used to facilitate cross-border payments, bond issuance, and insurance processes. This technology has also fostered the emergence of decentralized finance (DeFi), which allows financial operations, such as lending and asset tokenization, to be conducted without relying on traditional financial intermediaries. However, beyond this ambition of disintermediation, the economic and technical reality reveals a more nuanced landscape. While the original promise of blockchain was to eliminate trusted third parties, in practice we are witnessing a transformation rather than a disappearance of their role. The landscape of trust has been reshaped around new intermediaries, such as cryptocurrency exchanges, digital asset custodians, and stablecoin issuers, which now play central roles within the ecosystem. The adoption of blockchain technology nonetheless remains constrained by energy costs, scalability limitations, and strict regulatory requirements. Achieving a sustainable balance between performance, security, and compliance therefore represents a key challenge for blockchains in financial applications. In this context, this thesis explores how the judicious integration of trusted components can enhance the efficiency and resilience of financial blockchains. It makes three main contributions. First, we demonstrate that adding a trusted component to each node is insufficient to improve Byzantine Reliable Broadcast resilience: even with attestations preventing equivocation, the threshold remains at n >= 3t+1 because malicious processes retain the selective omission strategy. This negative result establishes that naive integration of trusted hardware is ineffective and that a fundamental protocol redesign is necessary. Second, it introduces new Byzantine Reliable Broadcast protocols that leverage a minimal trusted component, a Trusted Monotonic Counter at the initiator, to achieve optimal resilience with only n >= 2f+1 processes, while reducing message complexity by nearly half compared to classical approaches. Third, it introduces TenderTEE, a new consensus protocol extending Tendermint (recently renamed Ignite) through TEE attestations, thereby reducing the number of required validators and communication costs while maintaining both safety and liveness. TenderTEE not only decreases the number of necessary nodes (or, for a given number of nodes, increases Byzantine fault tolerance) but also enables governance schemes characteristic of financial systems, such as tripartite structures, which were previously infeasible under classical consensus protocols tolerating one-third of Byzantine nodes. In addition to that, the thesis provides broader design guidelines for building efficient blockchains in the financial sector, highlighting the complementary role of trusted components alongside Proof-of-Stake mechanisms, sharding, and optimistic protocols.