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Considering a scenario of anonymous data transfer between seller and buyer using proxies. If we consider that there are three proxies that are being selected by the buyer to obtain data from different sellers (like in emule), how can we make sure that these proxies do not collude with each other to obtain the copy that is being requested by buyer?

For example, if we use onion routing, then in this case, each of three proxies will have plain-text data at the end, and this plain-text data would be transferred to the buyer. What mechanism should we employ that will prevent the three proxies to collude? If they combine the files, they will get the copy of the same file being requested by buyer.

Thus as a solution, if we use end-to-end encryption, will the buyer and seller remain anonymous to each other?

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"the copy" of what "that is being requested by the buyer"? $\:$ –  Ricky Demer Mar 15 '13 at 14:53
    
@RickyDemer Copy of multimedia content that buyer has requested from seller through proxies. –  Alexandera Mar 15 '13 at 14:55
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I find this question poorly specified. I think you ought to pick a single system, and preferably explain about how the system is using the proxies (what properties they are needed for). I'm not familiar with Emule. Also I'm not sure what you mean by "the same copy"; this seems hard to square with Tor, because that's just not how Tor works. Also you need to separate out the multiple questions into different posts. –  D.W. Mar 15 '13 at 17:17
    
The question needs some more clarity - Can you define what a proxy is? Is it a site acting as a proxy to the seller or is it a real network proxy? If its a proxy seller then is it honoring the transaction or is the transaction routed to the seller to honor? If so is the proxy just making the transaction/purchase? What exactly are you trying to anonymize? The item purchased? The buyer? Both is my guess. Correct? –  R11 Apr 15 '13 at 18:05
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If the buyer is selecting proxies to use as trusted third parties, presumably the buyer needs to trust that at least one of them is honest and not colluding with the other three. Therefore, if you need to be sure that they're not colluding, the answer is that the buyer should choose the three proxies to ensure that they're not colluding.

Precisely how to do that depends upon the system and upon what knowledge the buyer has of the proxies. One scheme is to choose randomly from a list of vetted proxies, and count on the fact that most parties on that list are honest so it's unlikely that you (by chance) happen to pick three that are evil and colluding. Another is to choose three proxies who have a good reputation or who you have some other reason to trust. But ultimately, this is not so much a cryptographic question as it is a systems design question for the particular system.

No, end-to-end encryption on its own is not enough to guarantee anonymity. You need to also use some sort of system designed for anonymity, like Tor, and take other steps to protect your anonymity.

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Thanks a lot for your answer.What types of steps for anonymity do you recommend? –  Alexandera Mar 17 '13 at 17:21
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