Cryptographic Background Cryptography provides the following security services to the operating system and applications. In this chapter, we use the term entity to refer to both users and servers. Confidentiality Confidentiality ensures that only authorized entities have access to information. Keys are easier secrets to manage, especially since they can be exchanged in advance. The entity authentication service proves one entity s identity to another, and it is commonly implemented by demonstrating the possession of a secret.
Cryptography helps by keeping that secret private during the authentication process.
The integrity or data authentication service assures that a chunk of data did indeed originate from an entity and that it remains unaltered. Cryptography helps by binding the data to its originator. In some contexts, integrity might be defined only as ensuring that data remain unaltered. Nonrepudiation Nonrepudiation enables users to digitally sign electronic documents and be legally bound by the signatures, as if those signatures were handwritten. Cryptography can provide evidence that a user signed a document, but a lot of conditions need to be met for a court to consider this legally binding.