Modelling and verifying contract-oriented systems in Maude

We address the problem of modelling and verifying contractoriented systems, wherein distributed agents may advertise and stipulate contracts, but — differently from most other approaches to distributed agents — are not assumed to always behave “honestly”. We describe an executable specification in Maude of the semantics of CO2, a calculus for contract-oriented systems [6]. The honesty property [5] characterises those agents which always respect their contracts, in all possible execution contexts. Since there is an infinite number of such contexts, honesty cannot be directly verified by model-checking the state space of an agent (indeed, honesty is an undecidable property in general [5]). The main contribution of this paper is a sound verification technique for honesty. To do that, we safely over-approximate the honesty property by abstracting from the actual contexts a process may be engaged with. Then, we develop a model-checking technique for this abstraction, we describe an implementation in Maude, and we discuss some experiments with it

The Audit Logic: Policy Compliance in Distributed Systems

We present a distributed framework where agents can share data along with usage policies. We use an expressive policy language including conditions, obligations and delegation. Our framework also supports the possibility to refine policies. Policies are not enforced a-priori. Instead policy compliance is checked using an a-posteriri auditing approach. Policy compliance is shown by a (logical) proof that the authority can systematically check for validity. Tools for automatically checking and generating proofs are also part of the framework.\u

Distributed access control and the prototype of the Mojoy trust policy language

In a highly distributed computing environment, people frequently move from one place to another where the new system has no previous knowledge of them at all. Traditional access control mechanisms such as access matrix and RBAC depend heavily on central management. However, the identities and privileges of the users are stored and administered in different locations in distributed systems. How to establish trust between these strange entities remains a challenge. Many efforts have been made to solve this problem. In the previous work, the decentralised administration of trust is achieved through delegation which is a very rigid mechanism. The limitation of delegation is that the identities of the delegators and delegatees must be known in advance and the privileges must be definite. In this thesis, we present a new model for decentralised administration of trust: trust empowerment. In trust empowerment, trust is defined as a set of properties. Properties can be owned and/or controlled. Owners of the properties can perform the privileges denoted by the properties. Controllers of the properties can grant the properties to other subjects but cannot gain the privileges of the properties. Each subject has its own policy to define trust empowerment. We design the Mojoy tmst policy language that supports trust empowerment. We give the syntax, semantics and an XML implementation of the language. The Mojoy trust policy language is based on XACML, which is an OASIS standard. We develop a compliance checker for the language. The responsibility of the compliance checker is to examine the certificates and policy, and return a Boolean value to indicate whether the user's request is allowed. We apply our new model, the language and the compliance checker to a case study to show that they are capable of coping with the trust issues met in the distributed systems

Implementation of Smart Contracts Using Hybrid Architectures with On- and Off-Blockchain Components

Recently, decentralised (on-blockchain) platforms have emerged to complement centralised (off-blockchain) platforms for the implementation of automated, digital (smart) contracts. However, neither alternative can individually satisfy the requirements of a large class of applications. On-blockchain platforms suffer from scalability, performance, transaction costs and other limitations. Off-blockchain platforms are afflicted by drawbacks due to their dependence on single trusted third parties. We argue that in several application areas, hybrid platforms composed from the integration of on- and off-blockchain platforms are more able to support smart contracts that deliver the desired quality of service (QoS). Hybrid architectures are largely unexplored. To help cover the gap, in this paper we discuss the implementation of smart contracts on hybrid architectures. As a proof of concept, we show how a smart contract can be split and executed partially on an off-blockchain contract compliance checker and partially on the Rinkeby Ethereum network. To test the solution, we expose it to sequences of contractual operations generated mechanically by a contract validator tool.Comment: 12 pages, 7 figure

Service discovery and negotiation with COWS

To provide formal foundations to current (web) services technologies, we put forward using COWS, a process calculus for specifying, combining and analysing services, as a uniform formalism for modelling all the relevant phases of the life cycle of service-oriented applications, such as publication, discovery, negotiation, deployment and execution. In this paper, we show that constraints and operations on them can be smoothly incorporated in COWS, and propose a disciplined way to model multisets of constraints and to manipulate them through appropriate interaction protocols. Therefore, we demonstrate that also QoS requirement specifications and SLA achievements, and the phases of dynamic service discovery and negotiation can be comfortably modelled in COWS. We illustrate our approach through a scenario for a service-based web hosting provider