1、DATA ENCRYPTION STANDARD (DES) Federal Information Processing Standards Publications (FIPS PUBS) are issued by the National Bureau of Standards in accordance with section 111 (f) (2) of the Federal Property and Administrative Services Act of 1949, as amended, Public Law 89-306 (79 Stat 1127), Execut
2、ive Order 11717 (38 FR 12315, dated May 11, 1973), and Part 6 of Title 15 Code of Federal Regulations. （ 1） Name of Standard. Data Encryption Standard (DES). （ 2） Category of Standard. Computer Security. （ 3） Explanation. The Data Encryption Standard (DES) specifies a FIPS approved cryptographic alg
3、orithm as required by FIPS 140-1. This publication provides a complete description of a mathematical algorithm for encrypting (enciphering) and decrypting (deciphering) binary coded information. Encrypting data converts it to an unintelligible form called cipher. Decrypting cipher converts the data
4、back to its original form called plaintext. The algorithm described in this standard specifies both enciphering and deciphering operations which are based on a binary number called a key. A key consists of 64 binary digits (Os or 1s) of which 56 bits are randomly generated and used directly by the a
5、lgorithm. The other 8 bits, which are not used by the algorithm, are used for error detection. The 8 error detecting bits are set to make the parity of each 8-bit byte of the key odd, i.e., there is an odd number of 1s in each 8-bit byte1. Authorized users of encrypted computer data must have the ke
6、y that was used to encipher the data in order to decrypt it. The encryption algorithm specified in this standard is commonly known among those using the standard. The unique key chosen for use in a particular application makes the results of encrypting data using the algorithm unique. Selection of a
7、 different key causes the cipher that is produced for any given set of inputs to be different. The cryptographic security of the data depends on the security provided for the key used to encipher and decipher the data. Data can be recovered from cipher only by using exactly the same key used to enci
8、pher it. Unauthorized recipients of the cipher who know the algorithm but do not have the correct key cannot derive the original data algorithmically. However, anyone who does have the key and the algorithm can easily decipher the cipher and obtain the original data. A standard algorithm based on a
9、secure key thus provides a basis for exchanging encrypted computer data by issuing the key used to encipher it to those authorized to have the data. Data that is considered sensitive by the responsible authority, data that has a high value, or data that represents a high value should be cryptographi
10、cally protected if it is vulnerable to unauthorized disclosure or undetected modification during transmission or while in storage. A risk analysis should be performed under the direction of a responsible authority to determine potential threats. The costs of providing cryptographic protection using
11、this standard as well as alternative methods of providing this protection and their respective costs should be projected. A responsible authority then should make a decision, based on these analyses, whether or not to use cryptographic protection and this standard. （ 4） Approving Authority. Secretar
12、y of Commerce. （ 5） Maintenance Agency.U.S. Department of Commerce, National Institute of Standards and Technology, Computer Systems Laboratory. （ 6） Applicability. This standard may be used by Federal departments and agencies when the following conditions apply: An authorized official or manager re
13、sponsible for data security or the security of any computer system decides that cryptographic protection is required； The data is not classified according to the National Security Act of 1947, as amended, or the Atomic Energy Act of 1954, as amended. Federal agencies or departments which use cryptog
14、raphic devices for protecting data classified according to either of these acts can use those devices for protecting unclassified data in lieu of the standard. Other FIPS approved cryptographic algorithms may be used in addition to, or in lieu of, this standard when implemented in accordance with FI
15、PS 140-1. In addition, this standard may be adopted and used by non-Federal Government organizations. Such use is encouraged when it provides the desired security for commercial and private organizations. （ 7） Applications. Data encryption (cryptography) is utilized in various applications and envir
16、onments. The specific utilization of encryption and the implementation of the DES will be based on many factors particular to the computer system and its associated components. In general, cryptography is used to protect data while it is being communicated between two points or while it is stored in
17、 a medium vulnerable to physical theft. Communication security provides protection to data by enciphering it at the transmitting point and deciphering it at the receiving point. File security provides protection to data by enciphering it when it is recorded on a storage medium and deciphering it whe
18、n it is read back from the storage medium. In the first case, the key must be available at the transmitter and receiver simultaneously during communication. In the second case, the key must be maintained and accessible for the duration of the storage period. FIPS 171 provides approved methods for ma
19、naging the keys used by the algorithm specified in this standard. （ 8） Implementations. Cryptographic modules which implement this standard shall conform to the requirements of FIPS 140-1. The algorithm specified in this standard may be implemented in software, firmware, hardware, or any combination
20、 thereof. The specific implementation may depend on several factors such as the application, the environment, the technology used, etc. Implementations which may comply with this standard include electronic devices (e.g., VLSI chip packages), micro-processors using Read Only Memory (ROM), Programmab
21、le Read Only Memory (PROM), or Electronically Erasable Read Only Memory (EEROM), and mainframe computers using Random Access Memory (RAM). When the algorithm is implemented in software or firmware, the processor on which the algorithm runs must be specified as part of the validation process. Impleme
22、ntations of the algorithm which are tested and validated by NIST will be considered as complying with the standard. Note that FIPS 140-1 places additional requirements on cryptographic modules for Government use. Information about devices that have been validated and procedures for testing and valid
23、ating equipment for conformance with this standard and FIPS 140-1 are available from the National Institute of Standards and Technology, Computer Systems Laboratory, Gaithersburg, MD 20899. （ 9） Export Control. Cryptographic devices and technical data regarding them are subject to Federal Government
24、 export controls as specified in Title 22, Code of Federal Regulations, Parts 120 through 128. Some exports of cryptographic modules implementing this standard and technical data regarding them must comply with these Federal regulations and be licensed by the U.S. Department of State. Other exports
25、of cryptographic modules implementing this standard and technical data regarding them fall under the licensing authority of the Bureau of Export Administration of the U.S. Department of Commerce. The Department of Commerce is responsible for licensing cryptographic devices used for authentication, access control, proprietary software, automatic teller machines (ATMs), and certain devices used in other equipment and software. For advice concerning which agency has
