Encryption
Encryption has long been used by militaries and governments to facilitate secret communication. It is now commonly used in protecting information within many kinds of civilian systems. For example, the Computer Security Institute reported that in 2007, 71% of companies surveyed utilized encryption for some of their data in transit, and 53% utilized encryption for some of their data in storage. Encryption can be used to protect data "at rest", such as information stored on computers and storage devices (e.g. USB flash drives). In recent years, there have been numerous reports of confidential data, such as customers' personal records, being exposed through loss or theft of laptops or backup drives; encrypting such files at rest helps protect them if physical security measures fail. Digital rights management systems, which prevent unauthorized use or reproduction of copyrighted material and protect software against reverse engineering (see also copy protection), is another somewhat different example of using encryption on data at rest.
File hosting service
Secret key encryption is sometimes referred to as zero knowledge, meaning that only the user has the encryption key needed to decrypt the data. Since data is encrypted using the secret key, identical files encrypted with different keys will be different. To be truly zero knowledge, the file hosting service must not be able to store the user's passwords or see their data even with physical access to the servers. For this reason, secret key encryption is considered the highest level of access security in cloud storage. This form of encryption is rapidly gaining popularity, with companies such as SpiderOak being entirely zero knowledge file storage and sharing.