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Unformatted text preview: Computer and Network Security c circlecopyrt Copyright 2000 R. E. Newman Computer & Information Sciences & Engineering University Of Florida Gainesville, Florida 32611-6120 [email protected] Data Encryption Algorithm and Conventional Modern Cryptosystems (Pfleeger Ch. 3,4; KPS Ch. 3) 1 Enigma 1.1 History • Germans • Between WWI and WWII • automated symmetric encryption - an electromechanical device. • Variants used throughout WWII for communications – diplomatic – military – transatlantic communications cable • Polish obtained a commercial version • classified in the 1930’s • Polish mathematicians and machine flown to England • decisive impact on WWII 1.2 Enigma Structure overall similar a teletype. 1.2.1 General Operation 1. electrical connection made to send power 2. through a number of permutation components 3. finally lighting up an output light 4. also caused some wheels to turn, changing permutations 1.2.2 rotors 1. a disk with electrical contacts on each side 2. contacts connected via an internal permutation of wires 3. each contact had a symbol on rim of the disk, used to set key 4. rotors moved like an odometer when keys pressed 5. overall permutation would not repeat until they all returned to their original position (26 symbols ⇒ 26 r where r = number of rotors). 6. interchangeable - units were sent sets of rotors in a box 1.2.3 math • Rotors If a given rotor implements a permutation P , and R i is the i th rotation permutation R i ( n ) = n + i modulo N then the rotors implemented the concatenation of r permutations, each a rotation-permutation-inverse- rotation sequence, in which the rotation and its corresponding inverse rotation changed for one or more rotors for every plaintext character entered • exchange permutation reflector – special disk that just connected pairs of contacts on the same side and did not move....
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- Fall '08
- Cryptography, Encryption, Ri, DES Expansion Permutation, Feistel Structure