DES - Data Encryption Standard. A cipher developed by the United States government in the 1970s to be the official encryption algorithm of the U.S. 
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A widely-used method of data encryption using a private (secret) key that was judged so difficult to break by the U.S. government that it was restricted for exportation to other countries. There are 72,000,000,000,000,000 (72 quadrillion) or more possible encryption keys that can be used. For each given message, the key is chosen at random from among this enormous number of keys. Like other private key cryptographic methods, both the sender and the receiver must know and use the same private key. 
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Cryptographic algorithm designed by the National Bureau of Standards to encipher and decipher data using a 64bit key; specified in Federal Information Processing Standard Publication 46, dated January 15, 1977. There have been several modifications to this standard. 
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Data Encryption Standard (DES), in computer science, a commonly used, highly sophisticated algorithm developed by the United States National Institute of Standards and Technology for encrypting and decrypting data.
"Data Encryption Standard," Microsoft(R) Encarta(R) 96 Encyclopedia. (c) 1993-1995 Microsoft Corporation. All rights reserved.

The encoding system most widely used in the United States is the Data Encryption Standard (DES) designed by IBM and approved for use by the National Institute of Standards and Technology in 1976. DES involves a number of basic encrypting procedures that are then repeated several times.
"Computer Security," Microsoft(R) Encarta(R) 96 Encyclopedia. (c) 1993-1995 Microsoft Corporation. All rights reserved. (c) Funk & Wagnalls Corporation. All rights reserved.

In the early 1970s, LUCIFER, a cryptosystem that used both substitution and transposition was developed. In 1976, a cryptographic technique called the Data Encryption Standard (DES) was developed. DES was based on LUCIFER and makes use of the computer binary code consisting of 0's and 1's. Each unit is called a bit. DES transforms 64-bit message segments into 64-bit segments of ciphertext, using a 56-bit key. Each user randomly selects a key and reveals it only to those persons authorized to see the protected data. The actual message is encoded and decoded automatically by electronic devices attached to the sending and receiving computers. As there are more than 70 quadrillion possible 56-bit combinations, the chances of discovering a random key would seem remote. Nevertheless, DES has been challenged by some experts in the field as being too vulnerable to very high-power decoding methods developed for advanced computers.
Alternatives, such as public-key cryptosystems (PKC), which use both a public and a secret key, have been proposed. A PKC based on a mathematical "knapsack" approach eliminates a problem of key distribution but is not as computationally efficient as DES.
"Cryptography," Microsoft(R) Encarta(R) 96 Encyclopedia. (c) 1993-1995 Microsoft Corporation. All rights reserved. (c) Funk & Wagnalls Corporation. All rights reserved.

Data Encryption Standard (DES) is a widely-used method of data encryption using a private (secret) key that was judged so difficult to break by the U.S. government that it was restricted for exportation to other countries. There are 72,000,000,000,000,000 (72 quadrillion) or more possible encryption keys that can be used. For each given message, the key is chosen at random from among this enormous number of keys. Like other private key cryptographic methods, both the sender and the receiver must know and use the same private key. 
DES applies a 56-bit key to each 64-bit block of data. The process can run in several modes and involves 16 rounds or operations. Although this is considered "strong" encryption, many companies use "triple DES", which applies three keys in succession. This is not to say that a DES-encrypted message cannot be "broken." Early in 1997, RSA, owners of another encryption approach, offered a $10,000 reward for breaking a DES message. A cooperative effort on the Internet of over 14,000 computer users trying out various keys finally deciphered the message, discovering the key after running through only 18 quadrillion of the 72 quadrillion possible keys! Few messages sent today with DES encryption are likely to be subject to this kind of code-breaking effort. 
DES originated at IBM in 1977 and was adopted by the U.S. Department of Defense. It is specified in the ANSI X3.92 and X3.106 standards and in the Federal FIPS 46 and 81 standards. Concerned that the encryption algorithm could be used by unfriendly governments, the U.S. government has prevented export of the encryption software. However, free versions of the software are widely available on bulletin board services and Web sites. Since there is some concern that the encryption algorithm will remain relatively unbreakable, NIST has indicated DES may not be recertified as a standard and submissions for its replacement are being accepted. The next standard will be known as the Advanced Encryption Standard (AES). 
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Encryption is the conversion of data into a form, called a cipher, that cannot be easily understood by unauthorized people. Decryption is the process of converting encrypted data back into its original form, so it can be understood.
In order to easily recover the contents of an encrypted signal, the correct decryption key is required. The key is an algorithm that "undoes" the work of the encryption algorithm. Alternatively, a computer can be used in an attempt to "break" the cipher. The more complex the encryption algorithm, the more difficult it becomes to eavesdrop on the communications without access to the key.
In recent years, a controversy has arisen over so-called strong encryption. This refers to ciphers that are essentially unbreakable without the decryption keys. While most companies and their customers view it as a means of keeping secrets and minimizing fraud, some governments view strong encryption as a potential vehicle by which terrorists might evade authorities. These governments, including that of the United States, want to set up a key-escrow arrangement. This means everyone who uses a cipher would be required to provide the government with a copy of the key. Decryption keys would be stored in a supposedly secure place, used only by authorities, and used only if backed up by a court order. Opponents of this scheme argue that criminals could hack into the key-escrow database and illegally obtain, steal, or alter the keys. Supporters claim that while this is a possibility, implementing the key escrow scheme would be better than doing nothing to prevent criminals from freely using encryption/decryption.
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The Standard Data Encryption Algorithm, Harry Katzan Jr, Petrocelli Books, 1977 ISBN 0-89433-016-0 (APL). 
Computer Networks, Andrew S. Tanenbaum, Prentice Hall (both editions; second edition is ISBN 0-13-162959-X). (Pascal) 
Numerical Recipes, William H. Press et al, Cambridge University Press. (Fortran and Pascal version is ISBN 0-521-30811-9. Also in Numerical Recipes in C). 
UNIX System Security, Wood and Kachan, Hayden. ISBN 0-8104-6267-2. 
Byte Magazine, April 1977 (6502 Assembler). 
Cryptography: An Introduction to Computer Security, Seberry and Pieprzyk, Prentice Hall Australia. (C) 
Mathematical Cryptology for Computer Scientists and Mathematicians, Wayne Patterson, Rowman and Littlefield, 1987. ISBN 0-8476-7438-X. 
Introduction to the Analysis of the Data Encryption Standard (DES), Wayne G. Barker, ISBN 0-89412-169-3 (soft cover), 0-89412-170-7 (library bound), 1991, Aegean Park Press, Appendix G. (Basic, of all things). 
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Data Encryption Standard
http://www.itl.nist.gov/fipspubs/fip46-2.htm