applied cryptography - protocols, algorithms, and source code in c

The security of the former can probably be analyzed

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Unformatted text preview: and C additional values dependent on n, n1, n2, n3, n4; exactly which one depends on the parity of the iteration number. The important ideas in this design seem to be: 1. Use a large, secret, key-derived S-box (T). 2. Alternate arithmetic operations which don’t commute (addition and XOR). 3. Use an internal state maintained by the cipher which is not directly manifest in the data stream (the ni values which modify A and C at the end of each iteration). 4. Vary the round function according to the round number, and vary the iteration function according to the iteration number. Figure 17.1 The inner loop of SEAL. SEAL requires about five elementary machine operations to encrypt each byte of text. It runs at 58 megabits per second on a 50 megahertz 486 machine. This is probably the fastest software algorithm in the book. On the other hand, SEAL must preprocess its key into internal tables. These tables total roughly 3 kilobytes in size, and their calculation takes about 200 SHA computations. Thus, SEAL is not appropriate to use in situations where you don’t have the time to perform the key setup or you don’t have the memory to store the tables. Security of SEAL SEAL is a new algorithm and has yet to be subjected to any published cryptanalysis. This suggests caution. However, SEAL seems to be well thought through. Its peculiarities do, in the end, make a good deal of sense. And Don Coppersmith is generally regarded as the world’s cleverest cryptanalyst. Patents and Licenses SEAL is being patented [380]. Anyone wishing to license SEAL should contact the Director of Licenses, IBM Corporation, 500 Columbus Ave., Thurnwood, NY, 10594. 17.3 WAKE WAKE is the Word Auto Key Encryption algorithm, invented by David Wheeler [1589]. It produces a stream of 32-bit words which can be XORed with a plaintext stream to produce ciphertext, or XORed with a ciphertext stream to produce plaintext. And it’s fast. WAKE works in CFB; the previous ciphertext word is used to generate the next key word. It also uses an S-box of 256 32-b...
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