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Mohamed G. Gouda						Midterm 1
CS 395T: Network Protocol Security				Fall 2006
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Open Book							75 Minutes
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1. (10 points)

The "Key Grids" paper describes a family of log n protocols for assigning 
symmetric keys to the n processes in a network so that any two processes can
communicate securely using their assigned keys. Design a simple algorithm for
choosing one protocol from this family to assign symmetric keys to the 
processes in a given network. The inputs to this algorithm are n and r, where 
n is the number of processes in the given network, and r is the maximum number
of keys that can be assigned to each process in the given network.

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2. (10 points)

Consider a star network that consists of one center process p and eight
satellite processes q[0..7], and assume that the processes in this network are
assigned symmetric keys based on our logarithmic keying scheme. Each message
in this network is sent from p to all the satellite processes q[0..7] such 
that the message text is sent in the clear but the identities of the intended 
destinations of the message are kept hidden from the other satellite processes.
In other words, when a satellite process q[i] receives a message sent by p,
then q[i] can check whether or not q[i] is an intended destination of the 
message, but it cannot check whether any other satellite process q[j] is an
intended destination of the message. (If q[i] checks that it is an intended
destination of the message, then q[i] stores a copy of the message. Otherwise,
q[i] discards the received message.) Describe how can process p sends a 
message m whose intended destinations are the satellite processes q[0], q[1], 
q[2], q[3], and q[4] in this network. 

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