What kind of file encryption does Viber have?
Viber connections are heavily encrypted. Unfortunately, it's impossible to name the exact encryption method that's used, but most definitely it's AES-256 with other possible layers. This information is not available to public.
You can check their official “Are my messages secure?” page: https://support.viber.com/customer/portal/articles/1600146-are-my-messages-secure
