Which IP phone hardening technique will prevent call signaling and media stream tampering?

Which IP phone hardening technique will prevent call signaling and media stream tampering?

A.
disable GARP

B.
disable PC. to-voice VLAN access

C.
use MIC firmware images signed by Cisco

D.
store IP phone configuration files on the SFTP server

E.
deploy authentication and encryption between IP phones and Cisco Unified Communications Manager

Explanation:

Chapter 16: Implementing Security in CUCM pg.441
– IP Phone and the server can exchange SCCP or SIP signaling messages in a secure way by using TLS packet authentication and encryption.
– The authenticated and encrypted TLS session ensures the integrity and authenticity of each signaling message that is exchanged between the two devices.