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DES - The Data Encryption Standard

DES is a block cipher, which operates on 64-bit data fragments, using a 56-bit key. The basic DES algorithm is described as follows:
DES internal operation
Note that DES is designed so that decryption is performed by the exact same algorithm as encryption, using the same key -- hence a symmetric, single key cryptosystem.
 
The effectiveness of DES is based on the complexity of the 19 stages. In the above diagram, two identical 64-bit plaintexts will result in identical ciphertexts. This is called the Electronic Code Book (ECB) mode of operation.
 


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