Contingent payments on a public ledger: models and reductions for automated verification

Sergiu Bursuc (1) , Steve Kremer (1)

1 PESTO - Proof techniques for security protocols

We study protocols that rely on a public ledger infrastructure, concentrating on protocols for zero-knowledge contingent payment, whose security properties combine diverse notions of fairness and privacy. We argue that rigorous models are required for capturing the ledger semantics, the protocol-ledger interaction, the cryptographic primitives and, ultimately, the security properties one would like to achieve. Our focus is on a particular level of abstraction, where network messages are represented by a term algebra, protocol execution by state transition systems (e.g. multiset rewrite rules) and where the properties of interest can be analyzed with automated verification tools. We propose models for: (1) the rules guiding the ledger execution, taking the coin functionality of public ledgers such as Bitcoin as an example; (2) the security properties expected from ledger-based zero-knowledge contingent payment protocols; (3) two different security protocols that aim at achieving these properties relying on different ledger infrastructures; (4) reductions that allow simpler term algebras for homomorphic cryptographic schemes. Altogether, these models allow us to derive a first automated verification for ledger-based zero-knowledge contingent payment using the Tamarin prover. Furthermore , our models help in clarifying certain underlying assumptions, security and efficiency tradeoffs that should be taken into account when deploying protocols on the blockchain.

Domaines: Cryptographie et sécurité [cs.CR]

Sergiu Bursuc, Steve Kremer. Contingent payments on a public ledger: models and reductions for automated verification. ESORICS 2019 - The 24th European Symposium on Research in Computer Security, Sep 2019, Luxembourg, Luxembourg. ⟨hal-02269063⟩