Usable end-to-end security with Delta Chat and Chatmail

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Presented at Pass the SALT 2025 by

Holger Krekel

Over the years, Delta Chat has matured to be an easy-to-use, secure, and even fast decentralized FOSS messenger app for all platforms. In this talk we discuss two key security architectures: - Autocrypt and SecureJoin key distribution protocols for achieving automatic end-to-end encrypted messaging safe against MITM attacks, and - the open-signup Chatmail server network which successfully uses strict cryptographic interoperability contraints (DKIM, OpenPGP, TLS) instead of IP-reputation and spam classification methods. We also highlight the six independent security audits and analysis conducted so far.