net-im/viber requires: dev-libs/openssl-compat:1.0.0
For testing and developing purposes, you may download the viber.deb package from the official viber web site. The content of the .deb package can easily be extracted:
ar -x viber.deb
You will find a file: control.tar.gz. Exctract it and in it you will find the exact viber version number, which is no otherwise available on the Viber web site.