Secure communication
Encryption is a method in which data is rendered hard to read by an unauthorized party. Since encryption methods are created to extremely hard to break, many communication methods either use deliberately weaker encryption than possible, or have backdoors inserted to permit rapid decryption. In some cases government authorities have required backdoors be installed in secret. Many methods of encryption are also subject to "man in the middle" attack whereby a third party who can 'see' the establishment of the secure communication is made privy to the encryption method, this would apply for example to interception of computer use at an ISP. Provided it is correctly programmed, sufficiently powerful, and the keys not intercepted, encryption would usually be considered secure. The article on key size examines the key requirements for certain degrees of encryption security.
Encryption layer in storage stack
There is a plurality of terms that are used to describe implementations of disk encryption: on-the-fly encryption (OTFE); full disk encryption (FDE), whole disk encryption; filesystem-level encryption, encrypted filesystem, cryptographic filesystem, etc. All of them refer to an encryption layer in the storage stack. This article describes these techniques and explains their pros and cons. This article does not reference any software or hardware implementing these techniques (see disk encryption software and hardware), and it does not describe cryptographic theory behind it (see disk encryption theory).