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Unformatted text preview: e enter this country every day, and the Department of Immigration wants to make sure they are not smuggling cocaine. The officials could search everyone, but instead they use a probabilistic solution. They will search one-tenth of the people coming in. One person in ten has his belongings inspected; the other nine get through untouched. Chronic smugglers will get away with their misdeeds most of the time, but they have a 10 percent chance of getting caught. And if the court system is effective, the penalty for getting caught once will more than wipe out the gains from the other nine times. If the Department of Immigration wants to increase the odds of catching smugglers, they have to search more people. If they want to decrease the odds, they have to search fewer people. By manipulating the probabilities, they control how successful the protocol is in catching smugglers. The blind signature protocol works in a similar manner. Bob will be given a large pile of different blinded documents. He will open, that is examine, all but one and then sign the last. Think of the blinded document as being in an envelope. The process of blinding the document is putting the document in an envelope and the process of removing the blinding factor is opening the envelope. When the document is in an envelope, nobody can read it. The document is signed by having a piece of carbon paper in the envelope: When the signer signs the envelope, his signature goes through the carbon paper and signs the document as well. This scenario involves a group of counterintelligence agents. Their identities are secret; not even the counterintelligence agency knows who they are. The agency’s director wants to give each agent a signed document stating: “The bearer of this signed document, (insert agent’s cover name here), has full diplomatic immunity.” Each of the agents has his own list of cover names, so the agency can’t just hand out signed documents. The agents do not want to send their cover names to the agency; the enemy might h...
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- Fall '10