Unformatted text preview: s that guav a k (mod p) Then she sends Dave w. (5) Dave confirms that gw a l (mod p) y/hw a hubv (mod p) If they both check out, he accepts the signature as genuine. In another protocol Carol can convert the designatedconfirmer protocol into a conventional digital signature. See [333] for details. 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 © 19962000 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: Protocols, Algorthms, and Source Code in C (cloth)
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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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 23.6 Computing with Encrypted Data The Discrete Logarithm Problem
There is a large prime, p, and a generator, g. Alice has a particular value for x, and wants to know e, such that ge a x (mod p) This is a hard problem, and Alice lacks the computational power to compute the result. Bob has the power to solve the problem—he represents the government, or a large computing organization, or whatever. Here’s how Bob can do it without Alice revealing x [547,4]: (1) Alice chooses a random number, r, less than p. (2) Alice computes x' = xgr mod p (3) Alice asks Bob to solve ge' a x' (mod p) (5) Bob computes e' and sends it to Alice. (6) Alice recovers e by computing e = (e'  r) mod (p  1) Similar protocols for the quadratic residuosity problem and for the primitive root problem are in [3,4]. (See also Section 4.8.) 23.7 Fair Coin Flips
The following protocols allow Alice and Bob to flip a fair coin over a data network (see Section 4.9) [194]. This is an example of flipping a coin into a well (see Section 4.10). At first, only Bob knows the result of the coin toss and tells it to Alice....
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