11 Block ciphers
This chapter covers
- The DES and AES encryption standards
- Ciphers based on matrix multiplication
- Involutory ciphers, where encryption and decryption are identical
- Ripple ciphers
- Block chaining
We have already seen several ciphers that operate on text that has been divided into blocks of characters. Some operate on small blocks of just 2 or 3 characters, such as Playfair, Two Square, Three Square and Four Square. Some operate on longer blocks, but change only 2 or 3 characters at a time, such as bifid, trifid or FR-Actionated Morse. These ciphers act locally, on just one portion of each block. A change in one character of the plaintext typically changes at most 2 or 3 characters of the ciphertext.
This chapter deals with much ...
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