>E2E is hard when you have to route messages to multiple devices, ... OpenPGP has been dealing with multiple recipients since forever with no back channel even

>E2E is hard when you have to route messages to multiple devices, ... OpenPGP has been dealing with multiple recipients since forever with no back channel even. > ...aren't storing messages in a central server,... Who cares if we are doing E2E? > ...and those devices can be unavailable for indeterminate amounts of time and no guarantee that a subset of devices having the complete chat history will ever be on at the same time to sync. You only have to store the encrypted messages for each individual client until they connect again. If you are doing perfect forward secrecy then the client has to keep the decryption key around until the next connection so the server stored messages can be decoded. Then the key is destroyed.