End To End Encryption System Design Questions

Architectural design of systems providing encryption from source to destination. Key considerations: clear threat model definition, selection of encryption algorithms for different data types and threat levels, protocol design for secure communication, authentication mechanisms, integrity checking, managing forward/backward secrecy, and scalability to large user bases and data volumes. Understanding different deployment models (client-side, server-side, hybrid) and their security tradeoffs. Design considerations for systems protecting messages at rest and in transit.