# Mercy College Cryptography Programming Discussion

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fnawhxnyrk

Computer Science

Mercy College

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Cryptography Assignment on Block Ciphers 1. calculate a) 21 mod 2; b) -3 mod 4; c) 21003 mod 5 d) on GF(24) with m(x) = x4+x, find p(x) = 3x6-x5+x3+5x+5 mod m(x) 2. Use the attached example as work template to do S-AES a) The plain text is the first letter of students’ first name and the first letter of the last. For example, John Dole is JD. For Chinese names, use pinyin. Find the HEX value of the letters in the ASCII code table, and translate it into 16 bit string. b) The key is generated from their student ID like 1620106. Take the ID as a decimal integer, translate it into a binary number, and take the last 16 bits as the key. If the length is less than 16, add 0 in front of the bit stream. For example, if John Dole’s WID is 214348990, then its binary is 11001100 0110101101 0010111110. The last 16 bits is 1011010010111110. c) Using the above info to get the ciphertext. d) Using the above ciphertext and key to get the plaintext (challenging)
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Cryptography Discussion

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Cryptography Discussion
Assignment on Block Ciphers

1. calculate

a) 21 mod 2;

= 21/2 = 10.5, 10*2 = 20, 21- 20 =1

b) -3 mod 4; =

-3 + 4 mod 4=1 mod 4 = 1
c) 21003 mod 5=2^1 mod 5=2 mod 5=2 or -3

2^2 mod 5 =2^1 mod 5 * mod 2^1 mod 5=2*2 mod 5 =4 mod 5=-1 or 4

2^4 mod 5=2^2 mod 5 * 2^2 mod 5= -1 * -1 mod 5 =1 mod 5=1

2^8 mod 5 =2^4 mod 5 * 2^4 mod 5 =...

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