Measuring the Effects of Confidants on Privacy in Smart Contracts

Blockchain Systems provide highly welcome properties such as immutability, observability, availability, and distribution for implementing smart contracts without the need for intermediaries. While the smart contract goals of observability and enforceability can easily be achieved on blockchains, the goal of privity is much harder to tackle. In the context of smart contracts on blockchains, privity aims in limiting the spread of knowledge to the participants with a contractual need-to know. However, limiting access to data can limit the possible degrees of proactive enforcement of correct decisions and it can negatively impact their availability. Therefore, it can be required to find a proper balance between privity and enforceability or availability requirements. Designers may be forced to include additional participants (confidants) in the decision process only for the sake of enforceability or availability. In this paper, we introduce measures for assessing the impact of confidants for decisions within smart contracts on privacy. We model smart contracts in form of inter-organizational business processes and provide modeling constructs for privity requirements and the inclusion of confidants.