What is the function of a session key in encryption?

The function of a session key in encryption is to act as a temporary key specifically designed for a single session of communication. This means that each unique communication session can generate a new session key, enhancing security by limiting the exposure of the key to only that specific period of interaction. Using a unique session key for each communication minimizes the risk of a key being compromised and reused in future sessions, thereby providing a higher level of security.

In contrast, a permanent key for all communications would expose all sessions to a significant security risk if that key were to be compromised. This makes session keys a preferred choice in protocols like SSL/TLS, where each connection can securely use its own session key.

Other options, such as a method for data compression or a backup key for security, do not accurately reflect the role of a session key, as they relate to different security and data handling concepts altogether. The fundamental purpose of a session key is specifically for temporary encryption during a single session, emphasizing the notion of confidentiality for the duration of that communication only.