8.1 E2EE Zoom Phone Calls

The design of E2EE for Zoom Phone has very similar goals, threat models, and limitations as in Zoom Meetings. We wish to prevent even insiders with access to Zoom servers from compromising the confidentiality and integrity of E2E-encrypted Zoom Phone calls. Like Zoom Meetings, Zoom Phone has many features that are not compatible with strong cryptographic guarantees, such as dialing in from PSTN phones. Such features will be disabled when E2E is enabled. At the moment, we only support E2EE for calls between up to two Zoom Phone clients in the same account, which greatly simplifies the protocol.