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Mohamed Gouda							CS 386 S
Spring 2009							Quiz#1
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Consider the following two-step cascade protocol, similar to those defined in
the Dolev and Yao paper:

	x --> y : 	   D.x E.y E.x D.y d
	x <-- y :  E.x D.y D.x E.y E.x D.y d

Specify the steps that can be executed by an attacker t, other than x or y,
in order for t to obtain the data item d in this protocol.

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Student Name:
Student EID:
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Solution:

1. t obtains the message D.x E.y E.x D.y d, then applies E.x to it and gets
   E.y E.x D.y d. 

2. t pretends to be t and initiates the protocol with y:
   t(t) --> y :         E.y E.x D.y d
   t(t) <-- y : E.t D.y E.y E.x D.y d	
   t gets E.t E.x D.y d and applies D.t to it and gets E.x D.y d.

3. t pretends to be t and initiates the protocol with x:
   t(t) --> x :         E.x D.y d
   t(t) <-- x : E.t D.x E.x D.y d
   t gets E.t D.y d and applies D.t followed by E.y to it and gets d.

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