[asterisk-users] how to define a secure trunk

[Joao Pereira]

Hello
I would like to define a trunk from my Asterisk to a VoIP provider, but 
I want to make it secure, because its through the Internet.
I want to be sure no one makes calls as being me, and that my calls 
aren't intercepted.
Is it possible to define encrypted trunks? And should I define the trunk 
in SIP, IAX or something else?

Thanks
Joao Pereira