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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)
/** @module type/mpi */
var BigInteger = require('../crypto/public_key/jsbn.js'),
util = require('../util');
/**
* @class
* @classdescImplementation of type MPI (RFC4880 3.2)
* 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.
*/
module.exports = function mpi() {
/** An implementation dependent integer */
this.data = null;
/**
* Parsing function for a mpi (RFC 4880 3.2).
* @param {String} input Payload of mpi data
* @param {Integer} position Position to start reading from the input
* string
* @param {Integer} len Length of the packet or the remaining length of
* input at position
* @return {module:type/mpi} Object representation
*/
this.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;
}
this.fromBytes = function(bytes) {
this.data = new BigInteger(util.hexstrdump(bytes), 16);
}
this.toBytes = function() {
return this.write().substr(2);
}
this.byteLength = function() {
return this.toBytes().length;
}
/**
* Converts the mpi object to a string as specified in RFC4880 3.2
* @return {String} mpi Byte representation
*/
this.write = function() {
return this.data.toMPI();
}
this.toBigInteger = function() {
return this.data.clone();
}
this.fromBigInteger = function(bn) {
this.data = bn.clone();
}
}
</code></pre>
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