Data Encryption Standard
The Data Encryption Standard (DES) is a block cipher
Block cipher
In cryptography, a block cipher is a symmetric key cipher operating on fixed-length groups of bits, called blocks, with an unvarying transformation. A block cipher encryption algorithm might take a 128-bit block of plaintext as input, and output a corresponding 128-bit block of ciphertext...

 that uses shared secret
Shared secret
In cryptography, a shared secret is a piece of data, known only to the parties involved, in a secure communication. The shared secret can be a password, a passphrase, a big number or an array of randomly chosen bytes....

 encryption. It was selected by the National Bureau of Standards as an official Federal Information Processing Standard
Federal Information Processing Standard
A Federal Information Processing Standard is a publicly announced standardization developed by the United States federal government for use in computer systems by all non-military government agencies and by government contractors, when properly invoked and tailored on a contract...

 (FIPS) for the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 in 1976 and which has subsequently enjoyed widespread use internationally. It is based on a symmetric-key algorithm
Symmetric-key algorithm
Symmetric-key algorithms are a class of algorithms for cryptography that use trivially related, often identical, cryptographic keys for both encryption of plaintext and decryption of ciphertext. The encryption key is trivially related to the decryption key, in that they may be identical or there is...

 that uses a 56-bit key
56-bit encryption
In computing, 56-bit encryption refers to a key size of fifty-six bits, or seven bytes, for symmetric encryption. While stronger than 40-bit encryption, this still represents a relatively low level of security in the context of a brute force attack....

. The algorithm
In mathematics and computer science, an algorithm is an effective method expressed as a finite list of well-defined instructions for calculating a function. Algorithms are used for calculation, data processing, and automated reasoning...

 was initially controversial because of classified
Classified information
Classified information is sensitive information to which access is restricted by law or regulation to particular groups of persons. A formal security clearance is required to handle classified documents or access classified data. The clearance process requires a satisfactory background investigation...

 design elements, a relatively short key length, and suspicions about a National Security Agency
National Security Agency
The National Security Agency/Central Security Service is a cryptologic intelligence agency of the United States Department of Defense responsible for the collection and analysis of foreign communications and foreign signals intelligence, as well as protecting U.S...

 (NSA) backdoor.