# Handout 3 - CIS 3360 Security in Computing Spring 2010...

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CIS 3360 Security in Computing Spring 2010 Handout # 3 – Cryptography Examples Prepared by: Shafaq Chaudhry Caesar Cipher Encryption Example: Given the key 3, encrypt the message “department” using Caesar Cipher 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4 1 5 1 6 1 7 1 8 1 9 2 0 2 1 2 2 2 3 2 4 2 5 2 6 a b c d e f g h i j k l m n o p q r s t u v w x y z d = 4+3 mod 26 = 7 = g e = 5+3 mod 26 = 8 = h p = 16+3 mod 26 = 19 = s a = 1+3 mod 26 = 4 = d r = 18+3 mod 26 = 21 = u t = 20+3 mod 26 = 23 = w m = 13+3 mod 26 = 16 = p e = 5+3 mod 26 = 8 = h n = 14+3 mod 26 = 17 = q t = 20+3 mod 26 = 23 = w The encrypted message is “ghsduwphqw”. Decryption Example: Decrypt the message “hqhujbriifh” using Caesar Cipher and key of 3 h = 8-3 mod 26 = 5 = e q = 17-3 mo d26 = 14 = n h = 8-3 mod 26 = 5 = e u = 21-3 mod 26 = 18 = r j = 10-3 mod 26 = 7 = g b = 2 – 3 mod 26 = -1 mod 26 = 25 = y r = 18-3 mod 26 = 15 = o i = 9-3 mod 26 = 6 = f i = 9-3 mod 26 = 6 = f f = 6-3 mod 26 = 3 = c h = 8-3 mod 26 = 5 = e The decrypted message is “energyoffice”.

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Encryption Example 2: Encrypt the message “hello world” using Caesar cipher with key of 2. h = 8+2 mod 26 = 10 = j; e = 5+2 mod 26 = 7 = g ; l = 12+2 mod 26 = 14 = n ; o = 15+2 mod 26 = 17 = q; w = 23+2 mod 26 = 25 = y; r = 18+2 mod 26 = 20 = t ; d = 4+2 mod 26 = 6 = f The encrypted message is “jgnnq yqtnf”. Substitution Cipher Use the keyword PROGRAM to encrypt the message “national lab day”. Plaintext and ciphertext alphabet is shown below: a b c d e f g h i j k l m n o p q r s t u v w x y z p r o g a m b c d e f h i j k l n q s t u v w x y z So, the message “national lab day” becomes “jptdkjph hpr gpy”. Polyalphabetic Cipher Encrypt the message “this homework is good” using polyalphabetic ciphers method with key SECURITY. a b c d e f g h i j k l m n o p q r s t u v w x y z 0 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4 1 5 1 6 1 7 1 8 1 9 2 0 2 1 2 2 2 3 2 4 2 5 s e c u r i t y s e c u r i t y s e t h i s h o m e w o r k i s g o o d e e k m y w f c o s t e z a z m g h s+t = 18 + 19 = 37 mod 26 = 11 = l e+h = 4 + 7 = 11 mod 26 = 11 = l c+i = 2 + 8 = 10 mod 26 = 10 = k u+s = 20 +18 = 38 mod 26 = 12 = m r+h = 17 + 7 = 24 mod 26 = 24 = y i+o = 8 + 14 = 22 mod 26 = 22 = w t+m = 19 + 12 = 31 mod 26 = 5 = f y+e =24 + 4 = 28 mod 26 = 2 = c s+w = 18 + 22 = 40 mod 26 = 14 = o e+o = 4 + 14 = 18 mod 26 = 18 = s c+r = 2 + 17 = 19 mod 26 = 19 = t u+k = 20 + 10 = 30 mod 26 = 4 = e r+i = 17 + 8 = 25 mod 26 = 25 = z i+s = 8 + 18 = 26 mod 26 = 0 = a t+g = 19 + 6 = 25 mod 26 = 25 = z
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Handout 3 - CIS 3360 Security in Computing Spring 2010...

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