applied cryptography - protocols, algorithms, and source code in c

If alice doesnt ask to see the document and signs it

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Unformatted text preview: ave corrupted the agency’s computer. On the other hand, the agency doesn’t want to blindly sign any document an agent gives it. A clever agent might substitute a message like: “Agent (name) has retired and collects a million-dollar-a-year pension. Signed, Mr. President.” In this case, blind signatures could be useful. Assume that all the agents have 10 possible cover names, which they have chosen themselves and which no one else knows. Also assume that the agents don’t care under which cover name they are going to get diplomatic immunity. Also assume that the agency’s computer is the Agency’s Large Intelligent Computing Engine, or ALICE, and that our particular agent is the Bogota Operations Branch: BOB. (1) BOB prepares n documents, each using a different cover name, giving himself diplomatic immunity. (2) BOB blinds each of these documents with a different blinding factor. (3) BOB sends the n blinded documents to ALICE. (4) ALICE chooses n – 1 documents at random and asks BOB for the blinding factors for each of those documents. (5) BOB sends ALICE the appropriate blinding factors. (6) ALICE opens (i.e., she removes the blinding factor) n – 1 documents and makes sure they are correct—and not pension authorizations. (7) ALICE signs the remaining document and sends it to BOB. (8) Agent removes the blinding factor and reads his new cover name: “The Crimson Streak.” The signed document gives him diplomatic immunity under that name. This protocol is secure against BOB cheating. For him to cheat, he would have to predict accurately which document ALICE would not examine. The odds of him doing this are 1 in n—not very good. ALICE knows this and feels confident signing a document that she is not able to examine. With this one document, the protocol is the same as the previous completely blinded signature protocol and maintains all of its properties of anonymity. Previous Table of Contents Next Products | Contact Us | About Us | Privacy | Ad Info | Home Use of this site is subject to certain Terms & Conditions, Copyright © 1996-2000 EarthWeb Inc. All rights reserv...
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This note was uploaded on 10/18/2010 for the course MATH CS 301 taught by Professor Aliulger during the Fall '10 term at Koç University.

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