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Mohamed G. Gouda                                     Network Protocol Security
CS 395T                                              HW3 Solution
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1. 

Let u be a source and v be a destination. Also let B.tmp be a public
key of u chosen for this occasion.

Email:

u -> mix  : B.mix<r1,B.v<r0, M, B.mix'<r2,u>, B.tmp>,v>
mix -> v  : B.v<r0, M, B.mix'<r2,u>, B.tmp>

Reply:

v -> mix' : B.mix'<r2,u>, B.tmp<r3, M'>, B.tmp
mix' -> u : B.tmp<r4, B.tmp<r3, M'>>

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2.

See the following link:

http://www.cs.utexas.edu/users/gouda/problem2.pdf


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3.

Algorithm (mixed-match to first-match)
Input  : A mixed-match firewall f
output : A first-match firewall f' 

Let f' be a first-match firewall that has no rule initially.
Also let f" be a temporary firewall that has no rule initially.

For each rule r in f from the first rule to the last rule, 
    if rule r has label F, then add r to the end of f', 
    else if rule r has label L, then add r to the end of f".

For each rule r in f" from the last rule to the first rule,
    add r to the end of f'