Blockchain Based Auditable Access Control for Distributed Business Processes

Abstract

The use of blockchain technology has been proposed to provide auditable access control for individual resources. However, when all resources are owned by a single organization, such expensive solutions may not be needed. In this work we focus on distributed applications such as business processes and distributed workflows. These applications are often composed of multiple resources/services that are subject to the security and access control policies of different organizational domains. Here, blockchains can provide an attractive decentralized solution to provide auditability. However, the underlying access control policies may be overlapping in terms of the component conditions/rules, and simply using existing solutions would result in repeated evaluation of user's authorization separately for each resource, leading to significant overhead in terms of cost and computation time over the blockchain. To address this challenge, we propose an approach that formulates a constraint optimization problem to generate an optimal composite access control policy. This policy is in compliance with all the local access control policies and minimizes the policy evaluation cost over the blockchain. The developed smart contract(s) can then be deployed to the blockchain, and used for access control enforcement. We also discuss how the access control enforcement can be audited using a game-theoretic approach to minimize cost. We have implemented the initial prototype of our approach using Ethereum as the underlying blockchain and experimentally validated the effectiveness and efficiency of our approach.

Keywords: Access Control; Blockchain; Business Processes; Workflows; XACML.

Fig. 1.

Emergency Management Workflow

Fig. 2.

Assignment grading BP from virtual university domain

Fig. 3.

Access control policy graphs of a few services from assignment grading BP

Fig. 4.

Architectural view of the proposed approach for BP access control over blockchain

Fig. 5.

Global mediated access control policy graph shown in outermost dashed rectangular box, and fragments of composite access control policy shown in small rectangular boxes

Fig. 6.

Policy evaluation and enforcement mechanism for BP over blockchain

Fig. 7.

Cheating Detection Probability for different levels of cheating and different number of smart contracts checked

Fig. 8.

Minimum number of smart contracts that need to be verified to ensure sufficient detection probability

Fig. 9.

Cost comparison of Assignment Grading BP for 2500 Evaluations

Fig. 10.

Cost comparison of different degrees of overlap for 2500 Evaluations