Link Encryption is a technique in which a communication traveling along a network is encrypted and decrypted at every stage, or node. It is used to prevent traffic analysis and avoid human error.
With link encryption, a communication is encrypted at each node such as devices and network switches. At these points all of the information, including the header and routing information, undergoes this process. This helps prevent traffic analysis since the pattern can be infeasibly resistant to eavesdropping.
Link encryption differs from end-to-end encryption (E2EE) in that, with E2EE, the internal message but not header and routing information is encrypted. E2EE also ensures that the plaintext entered into the encryption system is only visible to the sender and recipient.
“Because link encryption encrypts header information as well as the internal message, and since it does so at every node, it frustrates traffic analysis. Eavesdroppers have no reasonable opportunity to study the sender and location information.”