Security in Computing, Third Edition

2.1. Terminology and Background

Consider the steps involved in sending messages from a sender, S, to a recipient, R. If S entrusts the message to T, who then delivers it to R, T then becomes the transmission medium. If an outsider, O, wants to access the message (to read, change, or even destroy it), we call O an interceptor or intruder. Any time after S transmits it via T, the message is vulnerable to exploitation, and O might try to access the message in any of the following ways:

• block it, by preventing its reaching R, thereby affecting the availability of the message

• intercept it, by reading or listening to the message, thereby affecting the confidentiality of the message

• modify it, by seizing the message and changing it in some way, affecting ...