Example shared key block cipher

Many kinds of shared clew block ciphers have been proposed in the letters, but there are really only three that are of significance in wireless Internet protocols: DES, Triple DES, and AES. The Digital Encryption Standard (DES) was published ~ the agency of the National Institute of Standards and Technology (NIST) in 1977 since use in commercial and  government applications. DES  the kind of looks like a 64-bit clew, of which only 56 bits indeed contribute to the security. The other 8 bits grant an odd parity bit in harvested land byte of the key. There are 16 DES keys that are wavering and not recommended for use.

When DES was originally proposed and with respect to many years thereafter, DES was thought to be secure because it was purpose highly unlikely that an attacker would be seized of cient computational resources to crack DES. A detailed parsing at the time estimated that it would cost $20 million to build a engine to crack DES, and require 12 hours, allowing that clear text/encrypted text pair was serviceable. By 1998, however, a small nonprgroup was ingenious to build a DES-cracking tool for about $250,000, of which $100,000 wanonrecurring design cost. The engine was able to a DES key in 4.5 days.

The cryptography common was well aware of the vitiation in DES security prior to 1998, in whatever degree, and the initial response was to standardize a variation of Dthat performed a DES encryption through one 56-bit key, followed ~ means of a decryption uanother 56-bit lock opener, followed by another encryption using the similar 56-bit key as inencryption. The overall decryption performs the inverse transformation.

The resultis called Triple DES and it increases the cogent number of bits in the explanation to 112.
An encrypt-decrypt-encrypt sequence with two keys was selected, more willingly than the mobvious two key encrypt-encrypt order of succession or adding more keys and else operations, due to some subtle attacks and likely negative impacts on particular applications. Since DES itself is not specifically to implement in software (though hardwimplementations areTriple DES is fair less so. The result was not particularly satisfying.

The cryptography community was well sensible of the deterioration in DES guarantee prior to 1998, however, and the at the head response was to standardize a diversity of Dthat performed a DES encryption with one 56-bit key, followed through a decryption uanother 56-bit key, followed by another encryption using the same 56-scrap key as inencryption. The overall decryption performs the reversed transformation. 

The resultis called Triple DES and it increases the adequate number of bits in the explanation to 112.
An encrypt-decrypt-encrypt succession with two keys was selected, moderately than the mobvious two key encrypt-encrypt succession or adding more keys and more operations, due to some subtle attacks and potential negative impacts on particular applications. Since DES itself is not specifically to implement in software (though hardwimplementations areTriple DES is flat less so. The result was not singly satisfying.