Viber Encryption Overview | Viber

Protocol document

Starting with Viber 6.0, all of Viber's core features are secured with end-to-end encryption: calls, one-on-one messages, group messages, media sharing and secondary devices.  This means that the encryption keys are stored only on the clients themselves and no one, not even Viber itself, has access to them.

Viber's protocol uses the same concepts of the "double ratchet" protocol used in Open Whisper Systems Signal application, however, Viber's implementation was developed from scratch and does not share Signal's source code.