122 lines
4.0 KiB
JavaScript
122 lines
4.0 KiB
JavaScript
// GPG4Browsers - An OpenPGP implementation in javascript
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// Copyright (C) 2011 Recurity Labs GmbH
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//
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// This library is free software; you can redistribute it and/or
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// modify it under the terms of the GNU Lesser General Public
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// License as published by the Free Software Foundation; either
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// version 2.1 of the License, or (at your option) any later version.
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//
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// This library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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// Lesser General Public License for more details.
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//
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// You should have received a copy of the GNU Lesser General Public
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// License along with this library; if not, write to the Free Software
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// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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/**
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* Implementation of the Sym. Encrypted Integrity Protected Data
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* Packet (Tag 18)<br/>
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* <br/>
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* RFC4880 5.13: The Symmetrically Encrypted Integrity Protected Data packet is
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* a variant of the Symmetrically Encrypted Data packet. It is a new feature
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* created for OpenPGP that addresses the problem of detecting a modification to
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* encrypted data. It is used in combination with a Modification Detection Code
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* packet.
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* @requires crypto
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* @requires util
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* @module packet/sym_encrypted_integrity_protected
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*/
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var util = require('../util'),
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crypto = require('../crypto');
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/**
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* @constructor
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*/
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module.exports = function () {
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/** The encrypted payload. */
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this.encrypted = null; // string
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/**
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* If after decrypting the packet this is set to true,
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* a modification has been detected and thus the contents
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* should be discarded.
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* @type {Boolean}
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*/
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this.modification = false;
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this.packets = null;
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this.read = function(bytes) {
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// - A one-octet version number. The only currently defined value is 1.
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var version = bytes.charCodeAt(0);
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if (version != 1) {
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throw new Error('Invalid packet version.');
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}
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// - Encrypted data, the output of the selected symmetric-key cipher
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// operating in Cipher Feedback mode with shift amount equal to the
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// block size of the cipher (CFB-n where n is the block size).
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this.encrypted = bytes.substr(1);
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};
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this.write = function() {
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// 1 = Version
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return String.fromCharCode(1) + this.encrypted;
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};
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this.encrypt = function(sessionKeyAlgorithm, key) {
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var bytes = this.packets.write();
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var prefixrandom = crypto.getPrefixRandom(sessionKeyAlgorithm);
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var prefix = prefixrandom + prefixrandom.charAt(prefixrandom.length - 2) + prefixrandom.charAt(prefixrandom.length -
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1);
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var tohash = bytes;
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// Modification detection code packet.
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tohash += String.fromCharCode(0xD3);
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tohash += String.fromCharCode(0x14);
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tohash += crypto.hash.sha1(prefix + tohash);
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this.encrypted = crypto.cfb.encrypt(prefixrandom,
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sessionKeyAlgorithm, tohash, key, false).substring(0,
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prefix.length + tohash.length);
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};
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/**
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* Decrypts the encrypted data contained in this object read_packet must
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* have been called before
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*
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* @param {Integer} sessionKeyAlgorithm
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* The selected symmetric encryption algorithm to be used
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* @param {String} key The key of cipher blocksize length to be used
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* @return {String} The decrypted data of this packet
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*/
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this.decrypt = function(sessionKeyAlgorithm, key) {
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var decrypted = crypto.cfb.decrypt(
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sessionKeyAlgorithm, key, this.encrypted, false);
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// there must be a modification detection code packet as the
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// last packet and everything gets hashed except the hash itself
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this.hash = crypto.hash.sha1(
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crypto.cfb.mdc(sessionKeyAlgorithm, key, this.encrypted) + decrypted.substring(0, decrypted.length - 20));
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var mdc = decrypted.substr(decrypted.length - 20, 20);
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if (this.hash != mdc) {
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throw new Error('Modification detected.');
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} else
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this.packets.read(decrypted.substr(0, decrypted.length - 22));
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};
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};
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