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The Data Encryption Standard (DES / ˌ d iː ˌ iː ˈ ɛ s, d ɛ z /) is a symmetric-key algorithm for the encryption of digital data. Although its short key length of 56 bits makes it too insecure for modern applications, it has been highly influential in the advancement of cryptography.
The "Left" and "Right" halves of the table show which bits from the input key form the left and right sections of the key schedule state. Note that only 56 bits of the 64 bits of the input are selected; the remaining eight (8, 16, 24, 32, 40, 48, 56, 64) were specified for use as parity bits.
The decryption was completed on January 19, 1999. In October of that year, DES was reaffirmed as a federal standard, but this time the standard recommended Triple DES. The small key space of DES and relatively high computational costs of Triple DES resulted in its replacement by AES as a Federal standard, effective May 26, 2002.
DES has a key schedule in which the 56-bit key is divided into two 28-bit halves; each half is thereafter treated separately. In successive rounds, both halves are rotated left by one or two bits (specified for each round), and then 48 round key bits are selected by Permuted Choice 2 (PC-2) – 24 bits from the left half and 24 from the right.
The earliest modes of operation, ECB, CBC, OFB, and CFB (see below for all), date back to 1981 and were specified in FIPS 81, DES Modes of Operation. In 2001, the US National Institute of Standards and Technology (NIST) revised its list of approved modes of operation by including AES as a block cipher and adding CTR mode in SP800-38A ...
In cryptography, Triple DES (3DES or TDES), officially the Triple Data Encryption Algorithm (TDEA or Triple DEA), is a symmetric-key block cipher, which applies the DES cipher algorithm three times to each data block.
56-bit DES encryption is now obsolete, having been replaced as a standard in 2002 by the 128-bit (and stronger) Advanced Encryption Standard. DES continues to be used as a symmetric cipher in combination with Kerberos because older products do not support newer ciphers like AES. [6]
The concept of public key cryptography was introduced by Whitfield Diffie and Martin Hellman in 1976. [3] At that time they proposed the general concept of a "trap-door one-way function", a function whose inverse is computationally infeasible to calculate without some secret "trap-door information"; but they had not yet found a practical example of such a function.