Which mode of IPsec is designed for end-to-end encryption of data?

The correct mode of IPsec designed for end-to-end encryption of data is Transport Mode. This mode focuses on securing the actual payload of the IP packets while leaving the header intact. By encrypting just the data within the IP packet, Transport Mode allows for efficient communication, especially in a situation where end systems (such as computers or servers) are communicating directly with each other.

Transport Mode is particularly useful for applications that need a secure channel for communication but do not require the additional overhead of encapsulating the entire IP packet, which is a characteristic of Tunnel Mode. This makes it suitable for scenarios where both ends of the conversation are aware of the IPsec processing and can handle the security measures accordingly.

In contrast, Tunnel Mode encapsulates the entire original IP packet within a new packet. This mode is more appropriate for site-to-site connections where the secure tunnel is established between two gateways, serving to protect the entire data being transmitted but focusing more on communications that traverse untrusted networks.

Choices that imply encryption modes or link layers do not specifically correspond to the specific functionalities and implementations of IPsec. Therefore, the unique attributes of Transport Mode make it the correct choice for scenarios requiring end-to-end encryption.