Unformatted text preview: are operated for them under contract. Adoption and use of this standard is available to private and commercial organizations. Before you run out and implement this standard in your next product, read the section on patent issues below. Description of DSA
DSA is a variant of the Schnorr and ElGamal signature algorithms, and is fully described in . The algorithm uses the following parameters: p = a prime number L bits long, when L ranges from 512 to 1024 and is a multiple of 64. (In the original standard, the size of p was fixed at 512 bits . This was the source of much criticism and was changed by NIST .) q = a 160-bit prime factor of p – 1. g = h(p-1)/q mod p, where h is any number less than p – 1 such that h(p - 1)/q mod p is greater than 1. x = a number less than q. y = gx mod p. The algorithm also makes use of a one-way hash function: H(m). The standard specifies the Secure Hash Algorithm, discussed in Section 18.7. The first three parameters, p, q, and g, are public and can be common across a network of users. The private key is x; the public key is y. To sign a message, m: (1) Alice generates a random number, k, less than q. (2) Alice generates r = (gk mod p) mod q s = (k-1 (H(m) + xr)) mod q The parameters r and s are her signature; she sends these to Bob. (3) Bob verifies the signature by computing w = s-1 mod q u1 = (H(m) * w) mod q u2 = (rw) mod q v = ((gu1 * yu2) mod p) mod q If v = r, then the signature is verified. 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)
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