First Examination
CIS 4363
February 20, 2007
Name____________________________________________________________
1. In this problem you will use a modified RC4 cipher. The text is encrypted at half a
byte, 4 bits, at a time. Let’s call half a byte, 4 bits, as a unit. Vector S will be 16unit
long, from S[0] to S[15]. Each S[i] will have 4 bits, containing a number from 0 to 15. K
will have a length equal or less then 16 units. Find the cipher text using the given K and
plaintext.
Assume that K is given in hex as xE3A.
(i) Provide the contents of T after initialization. (2 points)
(ii) Compute the contents of S after two iterations through the initial permutations of S. (4
points)
(iii) Assume that the results obtained in (ii) are used in stream generation. What is the
cipher text generated for the plaintext given in hex as xD5A. (9 points)
2. In this problem you will use a modified ECB cipher. Instead of encrypting 64 bits at a
time, encrypt a fixed length of characters at a time using Hill cipher. Find the cipher text
using the given Hill cipher key and plaintext.
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 Spring '07
 Staff
 Cryptography, Encryption, cipher text, Hill cipher key

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