Which protocol is primarily used for securing voice over IP (VoIP) communications?

The protocol primarily used for securing voice over IP (VoIP) communications is SRTP (Secure Real-time Transport Protocol). SRTP is specifically designed to provide encryption, message authentication, and integrity, which are essential for maintaining the confidentiality and integrity of voice communications over potentially insecure networks.

Voice traffic is sensitive and often transmitted in real-time, making it critical to protect it against eavesdropping and tampering. SRTP addresses these concerns by encrypting the voice packets and ensuring that they are sent securely, providing a much-needed layer of security for VoIP communications.

In contrast, other protocols mentioned serve different purposes. HTTPS is focused on securing web traffic, S/MIME is used for securing email messages, and FTPS is for securing file transfers. Consequently, SRTP stands out as the correct choice due to its specific design and function for safeguarding voice communications in the realm of VoIP.