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<h1 class="page-title">Source: crypto/public_key/elgamal.js</h1>
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<pre class="prettyprint source"><code>// GPG4Browsers - An OpenPGP implementation in javascript
// Copyright (C) 2011 Recurity Labs GmbH
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
//
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
// Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
//
// ElGamal implementation
/**
* @requires crypto/public_key/jsbn
* @requires crypto/random
* @requires util
* @module crypto/public_key/elgamal
*/
var BigInteger = require('./jsbn.js'),
random = require('../random.js'),
util = require('../../util');
function Elgamal() {
function encrypt(m, g, p, y) {
// choose k in {2,...,p-2}
var two = BigInteger.ONE.add(BigInteger.ONE);
var pMinus2 = p.subtract(two);
var k = random.getRandomBigIntegerInRange(two, pMinus2);
k = k.mod(pMinus2).add(BigInteger.ONE);
var c = [];
c[0] = g.modPow(k, p);
c[1] = y.modPow(k, p).multiply(m).mod(p);
return c;
}
function decrypt(c1, c2, p, x) {
util.print_debug("Elgamal Decrypt:\nc1:" + util.hexstrdump(c1.toMPI()) + "\n" +
"c2:" + util.hexstrdump(c2.toMPI()) + "\n" +
"p:" + util.hexstrdump(p.toMPI()) + "\n" +
"x:" + util.hexstrdump(x.toMPI()));
return (c1.modPow(x, p).modInverse(p)).multiply(c2).mod(p);
//var c = c1.pow(x).modInverse(p); // c0^-a mod p
//return c.multiply(c2).mod(p);
}
// signing and signature verification using Elgamal is not required by OpenPGP.
this.encrypt = encrypt;
this.decrypt = decrypt;
}
module.exports = Elgamal;
</code></pre>
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