Redactable signatures on data with dependencies and their application to personal health records

Storage of personal information by service providers risks privacy loss from data breaches. Our prior work on minimal disclosure credentials presented a mechanism to control the dissemination of personal information. In that work, personal data was broken into individual claims, which can be released in arbitrary subsets while still being cryptographically verifiable. In applying that work, we encountered the problem of connections between claims, which manifest as disclosure dependencies. In this work, we provide an efficient way to provide minimal disclosure, but with cryptographic enforcement of dependencies between claims, as specified by the claims certifier. This provides a mechanism for redactable signatures on data with disclosure dependencies. We show that an implementation of our scheme can verify thousands of dependent claims in tens of milliseconds. We also describe ongoing work in which the approach is being used within a larger system for dispensing personal health records.