Implementing end-to-end encryption for Dropbox teams

This post details the implementation of zero-knowledge, end-to-end encryption for Dropbox teams. It introduces a team-centric key management system where the team holds a central key, reducing individual user responsibility and the risk of data loss. The system supports automatic and manual device registration, with key rotation for security. Cryptographically, it uses AES-256-GCM for symmetric file encryption of 4MB blocks and Hybrid Public Key Encryption (HPKE) with P-256 curve, SHA-256, and AES-256-GCM for asymmetric key wrapping. The post also outlines limitations, such as device security, metadata visibility, and insider threats beyond external access controls.