System Administration Guide: Security Services

Encryption and Firewall Systems

Most local area networks transmit data between computers in blocks that are called packets. Through a procedure that is called packet smashing, unauthorized users from outside the network can corrupt or destroy data.

Packet smashing involves capturing the packets before the packets reach their destination. The intruder then injects arbitrary data into the contents, and sends the packets back on their original course. On a local area network, packet smashing is impossible because packets reach all systems, including the server, at the same time. Packet smashing is possible on a gateway, however, so make sure that all gateways on the network are protected.

The most dangerous attacks affect the integrity of the data. Such attacks involve changing the contents of the packets or impersonating a user. Attacks that involve eavesdropping do not compromise data integrity. An eavesdropper records conversations for later replay. An eavesdropper does not impersonate a user. Although eavesdropping attacks do not attack data integrity, the attacks do affect privacy. You can protect the privacy of sensitive information by encrypting data that goes over the network.