CompTIA Server+

Answer - B - Data encryption is not a function performed by a proxy server.

Key Takeaway: The typical functions of a proxy server include NAT, caching, and packet filtering. A proxy server is a server that acts as an intermediary for requests from clients seeking resources from other servers. A client connects to the proxy server, requesting some service, such as a file, connection, web page, or other resource, available from a different server. The proxy server evaluates the request according to its filtering rules.