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

G i37l and i37r but not i37l and i38r reveals alices

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Unformatted text preview: t the merchant or if the merchant tried to cheat the bank. This protocol corrects that: (1) Alice prepares 100 anonymous money orders for $1000 each. On each of the money orders she includes a different random uniqueness string, one long enough to make the chance of another person also using it negligible. (2) Alice puts one each, and a piece of carbon paper, into 100 different envelopes. She gives them all to the bank. (3) The bank opens 99 envelopes and confirms that each is a money order for $1000 and that all the random strings are different. (4) The bank signs the one remaining unopened envelope. The signature goes through the carbon paper to the money order. The bank hands the unopened envelope back to Alice and deducts $1000 from her account. (5) Alice opens the envelope and spends the money order with a merchant. (6) The merchant checks for the bank’s signature to make sure the money order is legitimate. (7) The merchant asks Alice to write a random identity string on the money order. (8) Alice complies. (9) The merchant takes the money order to the bank. (10) The bank verifies the signature and checks its database to make sure a money order with the same uniqueness string has not been previously deposited. If it hasn’t, the bank credits $1000 to the merchant’s account. The bank records the uniqueness string and the identity string in a database. (11) If the uniqueness string is in the database, the bank refuses to accept the money order. Then, it compares the identity string on the money order with the one stored in the database. If it is the same, the bank knows that the merchant photocopied the money order. If it is different, the bank knows that the person who bought the money order photocopied it. 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 reserved. Reproduction whole or in part in any form or medium without express written permission of EarthWeb is prohibited. Read EarthWeb's privacy statement. To access the contents, click the chapter and section titles. Applied Cryptography, Second Edition...
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