Which protocol is commonly used to encrypt data over a VPN?

IPsec is commonly used to encrypt data over a Virtual Private Network (VPN) because it provides end-to-end encryption for IP packets. By using IPsec, it ensures that the data integrity, authentication, and confidentiality of the communication are maintained over potentially unsecured networks, such as the Internet. This is pivotal for securing sensitive information exchanged between users or networks.

IPsec operates at the network layer and can secure multiple protocols by encapsulating and encrypting the data at the IP layer. It supports various encryption algorithms and can work in two modes: transport mode and tunnel mode. Transport mode only encrypts the data packet's payload, while tunnel mode encrypts the entire packet, making it suitable for site-to-site VPN connections.

While SSL can also secure data transmissions, especially in web traffic through HTTPS, IPsec is specifically designed for creating secure VPN connections. TCP and HTTP do not provide encryption capabilities on their own; TCP is a transport layer protocol used for reliable data transmission, and HTTP is an application layer protocol that transmits hypertext but lacks inherent security features. Thus, IPsec is recognized as the standard for VPN encryption due to its comprehensive security features explicitly designed for such applications.