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Mohamed G. Gouda				Solution of Midterm 1
CS 395T: Network Protocol Security		Fall 2006
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1. 

  if r >= n-1 -->	choose the first protocol in the protocol family

  [] r <  n-1 -->	compute the smallest k, if any, in the range 
			2..(log n) such that r >= 2k(k-1)(k-root n);
			if k exists --> choose the k-th protocol in the family
			[] no such k exists --> no protocol can be used
			fi
  fi

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2.

Process p sends two messages to every q[i] process. Each of the two messages
is of the following form:

	(m, md(0,0), md(0,1), md(1,0), md(1,1), md(2,0), md(2,1))

In the first message, each of the first five message digests md(i,j) is 
computed as follows.
 
        md(i,j) := MD.(m|S(i,j))

And the last message digest md(2,1) is assigned a random value. This first 
message is to be received by q[0], q[1], q[2], and q[3], and it is discarded
by q[4], q[5], and q[6].

In the second message, each of the message digests md(0,0), md(1,0), and 
md(2,1) is computed as follows.
 
        md(i,j) := MD.(m|S(i,j))

And the remaining three message digests are assigned random values. This 
second message is to be received by q[4], and it is discarded by all other 
q[i]'s.

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