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<h1 class="page-title">Source: type/mpi.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
// Hint: We hold our MPIs as an array of octets in big endian format preceeding a two
// octet scalar: MPI: [a,b,c,d,e,f]
// - MPI size: (a << 8) | b
// - MPI = c | d << 8 | e << ((MPI.length -2)*8) | f ((MPI.length -2)*8)
/**
* Implementation of type MPI ({@link http://tools.ietf.org/html/rfc4880#section-3.2|RFC4880 3.2})<br/>
* <br/>
* Multiprecision integers (also called MPIs) are unsigned integers used
* to hold large integers such as the ones used in cryptographic
* calculations.
* An MPI consists of two pieces: a two-octet scalar that is the length
* of the MPI in bits followed by a string of octets that contain the
* actual integer.
* @requires crypto/public_key/jsbn
* @requires util
* @module type/mpi
*/
module.exports = MPI;
var BigInteger = require('../crypto/public_key/jsbn.js'),
util = require('../util.js');
/**
* @constructor
*/
function MPI() {
/** An implementation dependent integer */
this.data = null;
}
/**
* Parsing function for a mpi ({@link http://tools.ietf.org/html/rfc4880#section3.2|RFC 4880 3.2}).
* @param {String} input Payload of mpi data
* @return {Integer} Length of data read
*/
MPI.prototype.read = function (bytes) {
var bits = (bytes.charCodeAt(0) << 8) | bytes.charCodeAt(1);
// Additional rules:
//
// The size of an MPI is ((MPI.length + 7) / 8) + 2 octets.
//
// The length field of an MPI describes the length starting from its
// most significant non-zero bit. Thus, the MPI [00 02 01] is not
// formed correctly. It should be [00 01 01].
// TODO: Verification of this size method! This size calculation as
// specified above is not applicable in JavaScript
var bytelen = Math.ceil(bits / 8);
var raw = bytes.substr(2, bytelen);
this.fromBytes(raw);
return 2 + bytelen;
};
MPI.prototype.fromBytes = function (bytes) {
this.data = new BigInteger(util.hexstrdump(bytes), 16);
};
MPI.prototype.toBytes = function () {
return this.write().substr(2);
};
MPI.prototype.byteLength = function () {
return this.toBytes().length;
};
/**
* Converts the mpi object to a string as specified in {@link http://tools.ietf.org/html/rfc4880#section-3.2|RFC4880 3.2}
* @return {String} mpi Byte representation
*/
MPI.prototype.write = function () {
return this.data.toMPI();
};
MPI.prototype.toBigInteger = function () {
return this.data.clone();
};
MPI.prototype.fromBigInteger = function (bn) {
this.data = bn.clone();
};
</code></pre>
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