What technology allows users to create an encrypted tunnel over an untrusted network?

A Virtual Private Network (VPN) is specifically designed to create an encrypted tunnel over untrusted networks, such as the internet. This technology allows users to securely connect to a private network while using a public network, ensuring that any data transmitted is encrypted and protected from potential interception. By establishing a VPN connection, users can send and receive data as if they were directly connected to a private network, maintaining confidentiality and integrity.

In contrast, Secure Socket Layer (SSL) is a protocol used to secure communications over a computer network but does not inherently create a tunnel like VPN does; it is more focused on securing individual communications between specific applications and is widely used in HTTPS.

Remote Desktop Protocol (RDP) allows users to connect to and control a computer remotely but does not provide the same level of network-wide encryption that a VPN offers, and its primary function is remote access rather than securing an entire network's traffic.

A firewall serves as a protective barrier that monitors and controls incoming and outgoing network traffic based on predetermined security rules. While it is crucial for network security, it does not create an encrypted tunnel for data transmission.

In summary, a VPN is the correct choice because it is specifically designed to provide a secure and encrypted connection over untrusted networks.