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

To foil the subliminal channel alice cannot be

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Unformatted text preview: ustavus Simmons [1458,1459,1460], uses the Ong-Schnorr-Shamir identification scheme (see Section 20.5). As in the original scheme, the sender (Alice) chooses a public modulus, n, and a private key, k, such that n and k are relatively prime. Unlike the original scheme, k is shared between Alice and Bob, the recipient of the subliminal message. The public key is calculated: h = -k2 mod n If Alice wants to send the subliminal message M by means of the innocuous message M', she first confirms that M' and n are relatively prime, and that M and n are relatively prime. Alice calculates S1 = 1/2 * ((M' /M + M)) mod n S2 = k/2 * ((M' /M - M)) mod n Together, the pair, S1 and S2, is the signature under the traditional Ong-Schnorr-Shamir scheme and the carrier of the subliminal message. Walter the warden (remember him?) can authenticate the message as described by the Ong-Schnorr-Shamir signature scheme, but Bob can do better. He can authenticate the message (it is always possible that Walter can make his own messages). He confirms that S12 - S2 2/k2 a M' (mod n) If the message is authentic, the receiver can recover the subliminal message using this formula: M = M'/(S1 + S2 k-1) mod n This works, but remember that the basic Ong-Schnorr-Shamir has been broken. 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: Protocols, Algorthms, and Source Code in C (cloth) Go! Keyword 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: Go! Previous Table of Contents Next ----------- ElGamal Simmons’s secon...
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