Unformatted text preview: rmission of EarthWeb is prohibited. Read EarthWeb's privacy statement. To access the contents, click the chapter and section titles. Applied Cryptography, Second Edition: Protocols, Algorthms, and Source Code in C (cloth)
Brief Full Advanced Search Search Tips (Publisher: John Wiley & Sons, Inc.) Author(s): Bruce Schneier ISBN: 0471128457 Publication Date: 01/01/96 Search this book:
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----------- For instance, Bob buys a legal copy of DEW. He can validate the signature on the software package whenever he wants. Then, Bob convinces Carol that he’s a salesman from the Alice Software Company. He sells her a pirated copy of DEW. When Carol tries to validate the signature with Bob, he simultaneously validates the signature with Alice. When Carol sends him the random number, he then sends it on to Alice. When Alice replies, he then sends the reply on to Carol. Carol is convinced that she is a legitimate buyer of the software, even though she isn’t. This attack is an instance of the chess grandmaster problem and is discussed in detail in Section 5.2. Even so, undeniable signatures have a lot of applications; in many instances Alice doesn’t want anyone to be able to verify her signature. She might not want personal correspondence to be verifiable by the press, be shown and verified out of context, or even to be verified after things have changed. If she signs a piece of information she sold, she won’t want someone who hasn’t paid for the information to be able to verify its authenticity. Controlling who verifies her signature is a way for Alice to protect her personal privacy. A variant of undeniable signatures separates the relation between signer and message from the relation between signer and signature . In one signature scheme, anyone can verify that the signer actually created the signature, but the cooperation of the signer is required to verify that the signature is valid for the message. A related notion...
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