Choreographic programming provides a high-level abstraction for writing distributed computations while ensuring deadlock-freedom by construction. HasChor, a Haskell-based choreographic programming framework, offers a practical implementation of these ideas but faces limitations in handling an arbitrary number of participants and optimizing the communication of branches. In this work, we introduce CloudChor, a set of extensions that enhance HasChor’s expressiveness and efficiency through the use of multiply-located values, allowing choreographies to distribute and collect data across multiple participants in a structured manner. Additionally, we refine HasChor’s branching mechanism through a lightweight static analysis, selectively propagating branching decisions only to relevant participants, reducing communication overhead. To strengthen theoretical guarantees, we establish a formal semantics for HasChor and our extensions, proving deadlock-freedom. Finally, we demonstrate the practicality of our enhancements by implementing a data clean room protocol using CloudChor. Our contributions improve the applicability of choreographic programming to cloud-based secure data collaborations, making it a stronger candidate for real-world deployments.

We present a new side-channel attack that targets one of the most fundamental software caches in modern computer systems: the operating system page cache. The page cache is a pure software cache that contains all disk-backed pages, including program binaries, shared libraries, and other files. On Windows, dynamic pages are also part of this cache and can be attacked as well, e.g., data, heap, and stacks. Our side channel permits unprivileged monitoring of accesses to these pages of other processes, with a spatial resolution of 4kB and a temporal resolution of 2µs on Linux (≤6.7 measurements per second), and 466ns on Windows 10 (≤223 measurements per second). We systematically analyze the side channel by demonstrating different hardware-agnostic local attacks, including a sandbox-bypassing high-speed covert channel, an ASLR break on Windows 10, and various information leakages that can be used for targeted extortion, spam campaigns, and more directly for UI redressing attacks. We also show that, as with hardware cache attacks, we can attack the generation of temporary passwords on vulnerable cryptographic implementations. Our hardware-agnostic attacks can be mitigated with our proposed security patches, but the basic side channel remains exploitable via timing measurements. We demonstrate this with a remote covert channel exfiltrating information from a colluding process through innocuous server requests.