Encryption has long been used by the military and governments to facilitate confidential communications. Encryption is commonly used today to protect a variety of information within civilian systems. For example, the Computer Security Association reported that in 2007, 71 of the companies surveyed used some encryption for data in transit and 53 used some encryption for data in storage. [1] Encryption can be used to protect data "resting" other files, on computers and storage devices (e.g. USB flash drives).

In recent years there have been many reports of clients having confidential personal data records compromised through lost or stolen laptops or backup drives. Encrypting the rest of such files should help protect them if measures of personal security fail. Digital rights management systems that protect against the unauthorized use or copying of material in copyright-protected software and against reverse engineering (see also copy protection) are another example of the use of data-at-rest encryption that makes a difference.

Encryption can also be used to protect data in transit, for example through data transfer networks (e.g. Internet, e-commerce), mobile phones, wireless microphones, wireless intercom systems, Bluetooth devices and bank ATMs. There have been many reports of data being intercepted in transit in recent years. Encrypting data in transit also helps protect it, as it is often difficult to secure physical access to all networks.

Encryption itself can protect the confidentiality of messages, but other techniques are also needed to protect the integrity and authenticity of the message, such as a verification message authentication code (Mac) or a digital signature. Standards and encryption software and hardware are widely used for encryption, but successfully using encryption to ensure security can be a challenging issue. An anti-skid design or implementation in the system can allow for a successful attack. Sometimes, an encryption is revoked without an adversary having direct access to the unencrypted information. See, for example, Traffic Analysis, TEMPEST or Trojans.