Redactable Signatures on Data with Dependencies

The storage of personal information by service providers entails a significant risk of privacy loss due to data breaches. One way to mitigate this problem is to limit the amount of personal information that is provided. Our prior work on minimal disclosure credentials presented a computationally efficient mechanism to facilitate this capability. In that work, personal data was broken into individual claims, which could be released in arbitrary subsets while still being cryptographically verifiable. In expanding the applications for that work, we encountered the problem of connections between different claims, which manifest as dependencies on the release of those claims. In this new work, we provide an efficient way to provide the same selective disclosure, but with cryptographic enforcement of dependencies between claims, as specified by the certifier of the claims. This constitutes a mechanism for redactable signatures on data with release dependencies. Our scheme was implemented and benchmarked over a wide range of input set sizes, and shown to verify thousands of claims in tens to hundreds of milliseconds. We also describe ongoing work in which the approach is being used within a larger system for holding and dispensing personal health records.