# Exam2Sols - CIS 3362 Exam #2 Modern Encryption Schemes...

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Date: 11/7/08 1) (5 pts) If the input to S-box 5 is 011011 in DES, what is the corresponding output? row = 01 (bits 1,6) col = 1101 (bits 2,3,4,5) The corresponding entry is 9 (1001). (Grading: -2 if wrong s-box, -2 if wrong bits) 2) (5 pts) Why do the numbers 8, 16, 24, 32, 40, 48, 56 and 64 not appear in the matrix PC-1 in DES? They are the parity bits and not part of the actual key. (All or nothing) 3) (10 pts) If we can check 100,000,000 keys a second, how long (in years, to the nearest year) would it take try all possible keys in DES? years days year hrs day hr keys keys 8 . 22 25 . 365 1 24 1 min 60 1 sec 60 min 1 sec / 100000000 2 56 × × × × Since the question asks to round, the answer desired is 23 years. (3 pts for the key space, 2 pts for dividing by 10 8 , 1 pt for each of the other factors and 1 pt for rounding.) 4) (8 pts) If the input block of text for DES is 11001011 01101010 00100111 11110000 11101000 10010110 11011100 01010011 what are the first eight bits of the output from the initial permutation (IP)? The first 8 bits are bits 58, 50, 42, 34, 26, 18, 10 and 2. Taking these bits from the

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## This note was uploaded on 07/13/2011 for the course CIS 3362 taught by Professor Staff during the Fall '08 term at University of Central Florida.

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Exam2Sols - CIS 3362 Exam #2 Modern Encryption Schemes...

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