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Explanation & Answer
Attached.
Running head: Computer Securities
1
Student Name:
Institution Affiliation:
Date:
COMPUTER SECURITIES
Question 1:
a. Consider the following plaintext “hello world”. What is the cipher text using
classical Caesar cipher?
Encryption (cipher Text) Ci=(p+3) mod 26.
Decryption(plain text) Pi=(Ci-3) mod 26.
Given plaintext: “h e l l o w o r l
d”
Cipher text: k h o o r z r u o g
Plain text : H cipher text is : k
P=7
C=(7+3) mod 26 =10 mod 26 =10( 10 is remainder) 10 th letter is k
Plain text: E cipher text is : h
P=4
C= (4+3) mod 26 =7 mod 26 =7 .7 th letter is
h
Plain text = L cipher text : O
C=(11+ 3) mod 26 =14 mod 26=14 . 14 th letter is o
Plain text = o cipher text : r
C=(14+ 3) mod 26 =17 mod 26=17 . 17 th letter is r
Plain text =w cipher text : z
C=(22+3) mod 26 = 25 mod 26 =25 . 25th letter is =z
Plain text = o cipher text : r
C=(14+ 3) mod 26 =17 mod 26=17 . 17 th letter is r
Plain text = r cipher text : u
C=(17+ 3) mod 26 =20 mod 26=20 . 14 th letter is
Plain text =L cipher text :o
u
2
COMPUTER SECURITIES
3
C=(11+3) mod 26 = 14 mod 26 =14 . 14th letter is =o
Plain text = d cipher text : g
C=(3+ 3) mod 26 =6 mod 26=6 . 6 th letter is g
Final cipher text is = k h o o r z u r o g
PLAIN
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cipher
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b. Consider the following plaintext “The boy has the bag” and key is “vig”. What is the
cipher text using Vigenere cipher?
plaintext : “ T h e b o y h a s t h e b a g”
KEY
:“ v i g v i g v i g v i g v i g "
cipher text: o p k ...