A G PENDIX C
PPENDIX
Simplified DES
C. 1 Review................................................................................................................... 2 C. 2 SDES Key Generation............................................................................................. 3 C. 3 SDES Encryption..................................................................................................... three or more Initial and Final Mixtures.................................................................................. 3 The Function fK....................................................................................................... 4 The Switch Function................................................................................................ 5 C. 4 Evaluation of Simplified DES...................................................................................... five C. your five Relationship to DES.................................................................................................. 6
William Stallings
Copyright 2006
Supplement to
Cryptography and Network Secureness, Fourth Release
Prentice Area 2006
ISBN: 0131873164
http://williamstallings.com/Crypto/Crypto4e.html
8/5/05
Simplified DES, developed by Professor Edward cullen Schaefer of Santa Albumina University [SCHA96], is definitely an educational rather than a secure encryption protocol. It has related properties and structure to DES with much smaller parameters. The reader will dsicover it helpful to work through an example by hand although following the debate in this Appendix.
C. 1 Overview
Physique C. you illustrates the general structure in the simplified KKLK, which all of us will make reference to as SDES. The SDES encryption algorithm takes an 8bit block of plaintext (example: 10111101) and a 10bit crucial as insight and makes an 8bit block of ciphertext as output. The SDES decryption algorithm takes an 8bit block of ciphertext plus the same 10bit key accustomed to produce that ciphertext while input and produces the initial 8bit block of plaintext. The security algorithm entails five features: an initial permutation (IP); a complex function marked fK, that involves both permutation and alternative operations and depends on an important input; an easy permutation function that buttons (SW) both the halves with the data; the function fK again; and ultimately a echange function that is the inverse of the initial permutation (IPвЂ“1). While was stated in Phase 2, the use of multiple periods of echange and substitution results in a much more complex protocol, which boosts the difficulty of cryptanalysis. The function fK takes while input not only the data getting through the security algorithm, although also a great 8bit crucial. The criteria could have been designed to work with a 16bit key, consisting of two 8bit subkeys, a single used for each occurrence of fK. On the other hand, a single 8bit key could have been used, while using same key used 2 times in the algorithm. A compromise is to use a 10bit crucial from which two 8bit subkeys are made, as portrayed in Number C. 1 . In this case, the key is first afflicted by a permutation (P10). A shift procedure is performed. The outcome of the move operation then passes by using a permutation function that creates an 8bit output (P8) for the first subkey (K1 ). The output in the shift operation also feeds into another shift and another instance of P8 to produce the other subkey (K 2 ). We can concisely express the encryption algorithm as a composition1 of features:
which can also be written because:
IP1 u fK2 o SW um fK1 um IP
(((
ciphertext sama dengan IP1 fK 2 SW fK1 (IP(plaintext ))
in which
(
K1 = P8 Shift (P10(key ))
!
(
(
)))
)
K2 = P8 Shift Shift( P10( key))
))
Decryption is also demonstrated in Figure C. 1 and is essentially the reverse of encryption:
(((
plaintext sama dengan IP1 fK1 SW fK 2 (IP(ciphertext ))
you
)))
Explanation:! f n and g are two functions, then this function N with the formula y sama dengan F(x) sama dengan I
g[f(x)] is...

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