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<h1 class="page-title">Source: crypto/public_key/dsa.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
//
// A Digital signature algorithm implementation
/**
* @requires crypto/hash
* @requires crypto/public_key/jsbn
* @requires crypto/random
* @requires util
* @module crypto/public_key/dsa
*/
var BigInteger = require('./jsbn.js'),
random = require('../random.js'),
hashModule = require('../hash'),
util = require('../../util.js'),
config = require('../../config');
function DSA() {
// s1 = ((g**s) mod p) mod q
// s1 = ((s**-1)*(sha-1(m)+(s1*x) mod q)
function sign(hashalgo, m, g, p, q, x) {
// If the output size of the chosen hash is larger than the number of
// bits of q, the hash result is truncated to fit by taking the number
// of leftmost bits equal to the number of bits of q. This (possibly
// truncated) hash function result is treated as a number and used
// directly in the DSA signature algorithm.
var hashed_data = util.getLeftNBits(hashModule.digest(hashalgo, m), q.bitLength());
var hash = new BigInteger(util.hexstrdump(hashed_data), 16);
var k = random.getRandomBigIntegerInRange(BigInteger.ONE.add(BigInteger.ONE), q.subtract(BigInteger.ONE));
var s1 = (g.modPow(k, p)).mod(q);
var s2 = (k.modInverse(q).multiply(hash.add(x.multiply(s1)))).mod(q);
var result = [];
result[0] = s1.toMPI();
result[1] = s2.toMPI();
return result;
}
function select_hash_algorithm(q) {
var usersetting = config.prefer_hash_algorithm;
/*
* 1024-bit key, 160-bit q, SHA-1, SHA-224, SHA-256, SHA-384, or SHA-512 hash
* 2048-bit key, 224-bit q, SHA-224, SHA-256, SHA-384, or SHA-512 hash
* 2048-bit key, 256-bit q, SHA-256, SHA-384, or SHA-512 hash
* 3072-bit key, 256-bit q, SHA-256, SHA-384, or SHA-512 hash
*/
switch (Math.round(q.bitLength() / 8)) {
case 20:
// 1024 bit
if (usersetting != 2 &&
usersetting > 11 &&
usersetting != 10 &&
usersetting < 8)
return 2; // prefer sha1
return usersetting;
case 28:
// 2048 bit
if (usersetting > 11 &&
usersetting < 8)
return 11;
return usersetting;
case 32:
// 4096 bit // prefer sha224
if (usersetting > 10 &&
usersetting < 8)
return 8; // prefer sha256
return usersetting;
default:
util.print_debug("DSA select hash algorithm: returning null for an unknown length of q");
return null;
}
}
this.select_hash_algorithm = select_hash_algorithm;
function verify(hashalgo, s1, s2, m, p, q, g, y) {
var hashed_data = util.getLeftNBits(hashModule.digest(hashalgo, m), q.bitLength());
var hash = new BigInteger(util.hexstrdump(hashed_data), 16);
if (BigInteger.ZERO.compareTo(s1) > 0 ||
s1.compareTo(q) > 0 ||
BigInteger.ZERO.compareTo(s2) > 0 ||
s2.compareTo(q) > 0) {
util.print_debug("invalid DSA Signature");
return null;
}
var w = s2.modInverse(q);
var u1 = hash.multiply(w).mod(q);
var u2 = s1.multiply(w).mod(q);
return g.modPow(u1, p).multiply(y.modPow(u2, p)).mod(p).mod(q);
}
/*
* unused code. This can be used as a start to write a key generator
* function.
function generateKey(bitcount) {
var qi = new BigInteger(bitcount, primeCenterie);
var pi = generateP(q, 512);
var gi = generateG(p, q, bitcount);
var xi;
do {
xi = new BigInteger(q.bitCount(), rand);
} while (x.compareTo(BigInteger.ZERO) != 1 && x.compareTo(q) != -1);
var yi = g.modPow(x, p);
return {x: xi, q: qi, p: pi, g: gi, y: yi};
}
function generateP(q, bitlength, randomfn) {
if (bitlength % 64 != 0) {
return false;
}
var pTemp;
var pTemp2;
do {
pTemp = randomfn(bitcount, true);
pTemp2 = pTemp.subtract(BigInteger.ONE);
pTemp = pTemp.subtract(pTemp2.remainder(q));
} while (!pTemp.isProbablePrime(primeCenterie) || pTemp.bitLength() != l);
return pTemp;
}
function generateG(p, q, bitlength, randomfn) {
var aux = p.subtract(BigInteger.ONE);
var pow = aux.divide(q);
var gTemp;
do {
gTemp = randomfn(bitlength);
} while (gTemp.compareTo(aux) != -1 && gTemp.compareTo(BigInteger.ONE) != 1);
return gTemp.modPow(pow, p);
}
function generateK(q, bitlength, randomfn) {
var tempK;
do {
tempK = randomfn(bitlength, false);
} while (tempK.compareTo(q) != -1 && tempK.compareTo(BigInteger.ZERO) != 1);
return tempK;
}
function generateR(q,p) {
k = generateK(q);
var r = g.modPow(k, p).mod(q);
return r;
}
function generateS(hashfn,k,r,m,q,x) {
var hash = hashfn(m);
s = (k.modInverse(q).multiply(hash.add(x.multiply(r)))).mod(q);
return s;
} */
this.sign = sign;
this.verify = verify;
// this.generate = generateKey;
}
module.exports = DSA;
</code></pre>
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