Replicated Data Types (RDTs) are a type of data structure that can be replicated over a network, where each replica can be kept (eventually) consistent with the other replicas. They are used in applications with intermittent network connectivity, since local (offline) edits can later be merged with the other replicas. Applications that want to use RDTs often have an inherent security component that restricts data access for certain clients. However, access control for RDTs is difficult to enforce for clients that are not running within a secure environment, e.g., web applications where the client-side software can be freely tampered with. In essence, an application cannot prevent a client from reading data which they are not supposed to read, and any malicious changes will also affect well-behaved clients. This paper proposes Secure RDTs (SRDTs), a data type that specifies role-based access control for offline-available JSON data. In brief, a trusted application server specifies a security policy based on roles with read and write privileges for certain fields of an SRDT. The server enforces read privileges by projecting the data and security policy to omit any non-readable fields for the user's given role, and it acts as an intermediary to enforce write privileges. The approach is presented as an operational semantics engineered in PLT Redex, which is validated by formal proofs and randomised testing in Redex to ensure that the formal specification is secure.

Reactive programming is a programming paradigm whereby programs are internally represented by a dependency graph, which is used to automatically (re)compute parts of a program whenever its input changes. In practice reactive programming can only be used for some parts of an application: a reactive program is usually embedded in an application that is still written in ordinary imperative languages such as JavaScript or Scala. In this paper we investigate this embedding and we distill "the awkward squad for reactive programming" as 3 concerns that are essential for real-world software development, but that do not fit within reactive programming. They are related to long lasting computations, side-effects, and the coordination between imperative and reactive code. To solve these issues we design a new programming model called the Actor-Reactor Model in which programs are split up in a number of actors and reactors. Actors and reactors enforce a strict separation of imperative and reactive code, and they can be composed via a number of composition operators that make use of data streams. We demonstrate the model via our own implementation in a language called Stella.