Link encryption operates on a hop-by-hop basis, securing data only over a specific physical link, such as between a workstation and a switch or between two routers. At each intermediate node (e.g., a router), the entire packet is decrypted so the device can read the header and routing information. The packet is then re-encrypted before being sent to the next hop. Because the data is in plaintext inside each intermediate device, it is not continuously encrypted from the original source to the final destination. Statement C describes end-to-end encryption, which is a different security mechanism.

A. This is a true statement. Link encryption is specifically applied to encrypt all data traffic traversing a single, specific communication link or path segment.
B. This is a true statement. The primary purpose of link encryption is to protect the confidentiality of data as it crosses a vulnerable link, directly countering eavesdropping.
D. This is a true statement. A defining feature of link encryption is that it encrypts the entire packet or frame, including headers, trailers, and routing information, not just the user payload.

1. Stallings, W. (2020). Cryptography and Network Security: Principles and Practice (8th ed.). Pearson. In Section 19.1, "Link-Versus End-to-End Encryption," the text states, "With link encryption, each vulnerable communications link is equipped on both ends with an encryption device... the message is decrypted and then encrypted again. Thus, the entire message is in the clear in each switch." This directly confirms that information is not encrypted for its entire journey (refuting C) and that all data, including headers, is encrypted on the link (supporting D).

2. Whitman, M. E., & Mattord, H. J. (2021). Principles of Information Security (7th ed.). Cengage Learning. In Chapter 8, "Cryptology," the distinction is made: "In link encryption, the data are encrypted right before they are placed on the physical communications link... In end-to-end encryption, the encryption is usually initiated at the OSI model’s application layer." This highlights that link encryption is tied to the link, not the entire journey.

3. Kurose, J. F., & Ross, K. W. (2021). Computer Networking: A Top-Down Approach (8th ed.). Pearson. Chapter 8, "Security in Computer Networks," discusses security at different layers. Link-layer security protocols like WPA3 are described as securing the link between a client and a wireless access point, but not beyond. This illustrates the hop-by-hop nature of link encryption, contrasting with end-to-end protocols like TLS.