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DES In Practice
The ECB mode of operation is now rarely used, since it is now
generally agreed that it is breakable given sufficient
resources.
In the Chain Block Cipher (CBC) mode, each block
of plaintext is exclusive-ORed with the ciphertext output from the
previous encryption operation. Thus, the next block of ciphertext
is a function of its corresponding plaintext, the 56-bit key and
the previous block of ciphertext. Identical blocks of plaintext no
longer generate identical ciphertext, which makes this system much
more difficult to break.
The CBC mode of DES is the normal technique used for encryption in
modern business data communications.
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