Simple Des
A P PENDIX C
PPENDIX
Simplified DES
C.1 Overview ...................................................................................................................2
C.2 S-DES Key Generation .............................................................................................3
C.3 S-DES Encryption .....................................................................................................3
Initial and Final Permutations ..................................................................................3
The Function fK .......................................................................................................4
The Switch Function ................................................................................................5
C.4 Analysis of Simplified DES ......................................................................................5
C.5 Relationship to DES ..................................................................................................6
William Stallings
Copyright 2006
Supplement to
Cryptography and Network Security, Fourth Edition
Prentice Hall 2006
ISBN: 0-13-187316-4 http://williamstallings.com/Crypto/Crypto4e.html 8/5/05
Simplified DES, developed by Professor Edward Schaefer of Santa Clara University [SCHA96], is an educational rather than a secure encryption algorithm. It has similar properties and structure to DES with much smaller parameters. The reader might find it useful to work through an example by hand while following the discussion in this Appendix.
C.1 Overview
Figure C.1 illustrates the overall structure of the simplified DES, which we will refer to as SDES. The S-DES encryption algorithm takes an 8-bit block of plaintext (example: 10111101) and a 10-bit key as input and produces an 8-bit block of ciphertext as output. The S-DES decryption algorithm takes an 8-bit block of ciphertext and the same 10-bit key used to produce that ciphertext as input and
PPENDIX
Simplified DES
C.1 Overview ...................................................................................................................2
C.2 S-DES Key Generation .............................................................................................3
C.3 S-DES Encryption .....................................................................................................3
Initial and Final Permutations ..................................................................................3
The Function fK .......................................................................................................4
The Switch Function ................................................................................................5
C.4 Analysis of Simplified DES ......................................................................................5
C.5 Relationship to DES ..................................................................................................6
William Stallings
Copyright 2006
Supplement to
Cryptography and Network Security, Fourth Edition
Prentice Hall 2006
ISBN: 0-13-187316-4 http://williamstallings.com/Crypto/Crypto4e.html 8/5/05
Simplified DES, developed by Professor Edward Schaefer of Santa Clara University [SCHA96], is an educational rather than a secure encryption algorithm. It has similar properties and structure to DES with much smaller parameters. The reader might find it useful to work through an example by hand while following the discussion in this Appendix.
C.1 Overview
Figure C.1 illustrates the overall structure of the simplified DES, which we will refer to as SDES. The S-DES encryption algorithm takes an 8-bit block of plaintext (example: 10111101) and a 10-bit key as input and produces an 8-bit block of ciphertext as output. The S-DES decryption algorithm takes an 8-bit block of ciphertext and the same 10-bit key used to produce that ciphertext as input and