Papers

Projects 📦 CoverDrop & SecureMessaging CoverDrop (or SecureMessaging) is a whistleblowing system that integrates into a news app and provides a highly secure channel for whistleblowers to submit information to journalists. It launched in June 2025 and is based on previous academic research (see below). The implementation white paper and the coverdrop.org website provide many details about the system and its design. Sloth Sloth is a library for key-stretching and plausibly-deniable encryption using the Secure Element on smartphones. By using the Secure Element, Sloth can provide effective rate-limiting against adversaries with physical access to the device and large computational resources. It is implemented for Android and iOS and deployed to hundreds of thousands of devices through CoverDrop. Steuerlotse Steuerlotse is a prototype website created during the Tech4Germany fellowship. It integrates with the official German tax API Elster through ERiC and Python’s ctypes. We presented it to the Federal Minister of Finance, Olaf Scholz, in 2020 and its successor was deployed to production in 2021. Argon2Kt Argon2Kt is an Android/Kotlin binding for the Argon2 password hash algorithm (winner of the PHC). This is a personal project of mine. I have written this blog article which explains more about password hashing on Android. Spectrum & Fresco Spectrum is a cross-platform, declarative image transcoding library written in C++ with bindings for Android and iOS. The release blog post provides a good introduction. I am one of its original authors. ...