IM Chat messages should be end-to-end encrypted at the application layer using TLS 1.2 with Advanced Encryption Standard (AES) 256-bit algorithm.
Meeting/Webinars/Chat media streams are using transport encryption, where a symmetric key is negotiated using https with Zoom servers and video and audio payload is encrypted using AES 256-bit algorithm with that key. Please read more details at The Intercept article and Zoom article: The Facts Around Zoom and Encryption for Meetings/Webinars.
For dial-in participants joining by phone, the audio is encrypted until it leaves Zoom’s data centers and is transferred to the participant’s phone network.
H323/SIP devices are not enforced to join using encryption as we expect some issues with very old models.
Please check Official Statement: EU GDPR Compliance.