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Mohamed G. Gouda					Solutions to Midterm 3
CS 395T: Network Protocol Security			Fall 2006
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1.

"rp.i implies mp.j" iff 
(S.1 is-subset T.1  ^  ...  ^ S.d is-subset T.d)

"no packet satisfies both rp.i and mp.j" iff 
(There is k, 1 =< k =< d, S.k intersection T.k is empty)

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2. 

Assume the voting sever gets a copy of a message m that is sent from some 
voter particular v to the mix server in the first version of the protocol. 
The voting server knows all the submitted pairs (nonce n, myvote), and it 
knows B.mix and B.voting. Thus the voting server can try all possibilities to 
find out the pair (nonce n, myvote) such that 

	B.mix<B.voting<nonce n, myvote>> = m

In this case, the voting server knows the myvote of voter v. This scenario
does not work in the second protocol since number of all possible values of 
rand is very large.

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3.

voter v--> mix    :  B.mix<rand, B.voting<nonce n, myvote, B.mix'<rand',v>>>

mix    --> voting :  B.voting<nonce n, myvote, B.mix'<rand',v>>

voting --> mix'   :  B.mix'<R.voting<MD(nonce n | myvote)>>, B.mix'<rand',v>

mix'   --> voter v:  rand'<R.voting<MD(nonce n | myvote)>>

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