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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:
- The substitution stages in DES involve re-arranging the order
of the bits from the previous stage, and using the
XOR function to combine them with the key.
- The transposition stages re-arrange (ie, swap) the positions of
all of the 64 bits.
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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