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The Advanced Encryption Standard

The Data Encryption Standard, or DES, specified a block cipher with a 56-bit key that operated on 64-bit blocks. It was developed by IBM, in response to a request from the National Bureau of Standards for a cryptographic algorithm . . .
The Data Encryption Standard, or DES, specified a block cipher with a 56-bit key that operated on 64-bit blocks. It was developed by IBM, in response to a request from the National Bureau of Standards for a cryptographic algorithm to protect the "sensitive but unclassified" communications of the U.S. government.

Because of advances in the speed of computers, a cipher having only a 56-bit key is no longer secure. One response to this has been the use of Triple-DES. The standard method of using Triple-DES is to encrypt a 64-bit block with DES using one key, decrypt it with another, and then encrypt it again either with the first key or with a third key. This gives a key length of either 112 bits or 168 bits; in addition, if all three 56-bit keys are the same, the decryption in the middle will undo one of the encryptions, allowing interoperability with equipment using ordinary DES.

The link for this article located at SecurityFocus --   is no longer available.

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