Ethereum has recently switched to a Proof of Stake consensus protocol called Gasper. We analyze Gasper using PRISM+ , an extension of the probabilistic model checker PRISM with primitives for modeling blockchain data types . PRISM+ is therefore used to rapidly and automatically analyze the robustness of Gasper when tuning, up or down, several basic parameters of the protocol, such as network latencies and number of validators. We also study the effectiveness of Gasper in updating stakes and its resilience to three attacks: the balance, bouncing and time attacks.

International audience

Hybrid Casper is the new Ethereum blockchain protocol that uses both Proof of Work and Proof of Stake to reach a consensus between nodes. Here, we analyze the protocol using PRISM+ , an extension of the probabilistic model checker PRISM with primitives for expressing blockchain data types. First, we extend PRISM+ to include data types and operations for modeling and analyzing Proof of Stake based consensus protocols. Then, we model Hybrid Casper in PRISM+ as a parallel composition of stochastic processes, thus precisely describing the behavior of the protocol and highlighting its corner cases. PRISM+ is therefore used to rapidly and automatically analyze the resilience of Hybrid Casper when tuning, up or down, several basic parameters of the protocol, such as the rates of creating blocks, and the strategies for determining penalties. Finally, we study the robustness of Hybrid Casper to two well-known attacks: the Eclipse attack and the majority attack.

We present Stipula, a domain specific language that may assist legal practitioners in programming legal contracts through specific patterns. The language is based on a small set of programming abstractions that correspond to common patterns in legal contracts. We illustrate the language by means of two paradigmatic legal contracts: a bike rental and a bet contract. Stipula comes with a formal semantics, an observational equivalence and a type inference system, that provide for a clear account of the contracts' behaviour and illustrate how several concepts from concurrency theory can be adapted to automatically verify the properties and the correctness of software-based legal contracts. We also discuss a prototype centralized implementation of Stipula.