Key Transparency Comes to Messenger
Nov 20, 2025Dillon George, Artem Ignatyev, Kevin Lewi, Yihai Long, Jeff Lu
Summary
Introduced key transparency verification for end-to-end encrypted chats on Messenger, building upon WhatsApp's implementation. This feature provides users with an auditable record of public keys to verify that their conversations are encrypted with the correct keys and haven't been tampered with. The implementation leverages the Auditable Key Directory (AKD) library and Cloudflare's key transparency auditor. Engineering challenges addressed include handling a high volume and frequency of key updates (approx. 2-minute epoch frequency, hundreds of thousands of new keys per epoch) by optimizing AKD for smaller proof sizes and improving infrastructure resilience to outages and sequencing delays.
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