Download presentation

Presentation is loading. Please wait.

Published byAnnabel Stapley Modified over 2 years ago

1
Lecture 3 Classical Cipher System SUBSTITUTION CIPHERS By: NOOR DHIA AL- SHAKARCHY 2012-2013

2
Classical cipher system substitutiontransposition Homophoni c polyalphabeti c polygram simple shifteddecimatio n affin Key word mix Beal High- order Vigene re BeafortVariant beaufort Hill Play Fair

3
5- POLYGRAM SUBSTITUTION CIPHERS: PolyGram substitution ciphers are ciphers in which group of letters are encrypted together, and includes enciphering large blocks of letters. Play Fair: 1- if m1,m2 in same row, then c1, c2 are the two characters to the right of m1, m2 respectively. 2- If m1, m2 in the same column, then c1, c2 are below the m1,m2. 3- If m1, m2 are in different rows and columns then c1, c2 are the other corners of rectangle. 4- If m1=m2 a null character (e.g. x) is inserted in the plaintext between m1, m2 to eliminate the double. 5- If the plaintext has an odd number of characters a null character is appended to the end of the plaintext.

4
Example: ∑ =A…Z M = RENAISSANCE 5- POLYGRAM SUBSTITUTION CIPHERS: - Play Fair: HARPS ICODB EFGKL MNQTU VWXYZ K = M = RE NA IS SA NC EX Ek(M)= C= HG WC BH HR WF GV

5
5- POLYGRAM SUBSTITUTION CIPHERS: Hill Ciphers: Let d=2, M= m1 m2, C= c1, c2 where: C1 =( k 11 m1 +k 12 m 2 ) mod n C2 =(k 21 m1 +k 22 m 2 ) mod n K11k12 K21K22 Where K = C1 C2 K11k12 K21K22 m1 m2 That is : = * mod n Ek(M) = K*M Dk(C) = K -1 *C mod n = K -1 K M mod n = M Where K.K -1 mod n = I (Identical matrix)

6
5- POLYGRAM SUBSTITUTION CIPHERS: Example: ∑ =A…Z M = EG K K -1 I 32 35 1520 179 10 01 Mod 26 = M = E G = 4 6 C1 C2 32 35 4 6 24 16 Y Q = * mod 26 = = To decipher:- m1 m2 1520 179 24 16 4 6 E G = * mod 26 = =

Similar presentations

Presentation is loading. Please wait....

OK

Section 2.9 The Hill Cipher; Matrices

Section 2.9 The Hill Cipher; Matrices

© 2017 SlidePlayer.com Inc.

All rights reserved.

Ads by Google

Start a ppt on a remote computer Ppt on general electric company Ppt on programmable logic array programmer Ppt on resistance temperature detector definition Ppt on traction rolling stock wheels Easy ppt on global warming Ppt on hvdc system in india Ppt on agriculture system in india Ppt on eid festival pictures Ppt on smoking is injurious to health