Encryption is the primary function related to securing data and ensuring confidentiality at the Presentation Layer of the OSI model. This layer is responsible for transforming data into a format that can be properly encrypted before transmission on the network. Compression primarily reduces the size of the data for faster transmission but does not enhance security. Media conversion does not relate directly to security; it pertains more to compatibility between different types of data formats. Session management occurs at the Session Layer (Layer 5), not the Presentation Layer.