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Unformatted text preview: do ElGamal encryption of message m with public key y, choose a random number, k, and call DSAsign (p,p,g,k,0,0,r,s) The value of r returned is a in the ElGamal scheme. Throw s away. Then, call DSAsign (p,p,y,k,0,0,r,s) Rename the value of r to be u; throw s away. Call DSAsign (p,p,m,1,u,0,r,s) Throw r away. The value of s returned is b in the ElGamal scheme. You now have the ciphertext, a and b. Decryption is just as easy. Using secret key x, and ciphertext messages a and b, call DSAsign (p,p,a,x,0,0,r,s) The value r is ax mod p. Call that e. Then call DSAsign (p,p,1,e,b,0,r,s) The value s is the plaintext message, m. This method will not work with all implementations of DSA. Some may fix the values of p and q, or the lengths of some of the other parameters. Still, if the implementation is general enough, this is a way to encrypt using nothing more than digital signature function. RSA Encryption with DSA
RSA encryption is even easier. With a modulus n, message m, and public key e, call DSAsign (n,n,m,e,0,0,r,s) The value of r returned is the ciphertext. RSA decryption is the same thing. If d is the private key, then DSAsign (n,n,m,d,0,0,r,s) returns the plaintext as the value of r. Security of DSA
At 512bits, DSA wasn’t strong enough for longterm security. At 1024 bits, it is. 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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 Cryptography

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