Cryptographically Enforced Orthogonal Access Control at Scale

We propose a new approach to cryptographically enforced data access controls that uses public key cryptography to secure large numbers of documents with arbitrarily large numbers of authorized users. Our approach uses a proxy re-encryption (PRE) scheme to handle the problems typical of public key cryptography including key management, rotation, and revocation, in a highly scalable way, while providing end-to-end encryption and provable access. In this paper we describe a system based on this approach. We call it an orthogonal access control system, because it allows the decision about the groups to which to encrypt a piece of data to be made independently and asynchronously from the decision about who belongs to a group and can therefore decrypt the data. We define specific requirements for a PRE scheme needed to support the system, and we provide a specific instance that meets these requirements. We detail the algorithms that make up the scheme, and we present an enhancement that provides better revocability of keys.