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<h1 class="page-title">Source: packet/sym_encrypted_integrity_protected.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
/**
* Implementation of the Sym. Encrypted Integrity Protected Data
* Packet (Tag 18)<br/>
* <br/>
* {@link http://tools.ietf.org/html/rfc4880#section-5.13|RFC4880 5.13}:
* The Symmetrically Encrypted Integrity Protected Data packet is
* a variant of the Symmetrically Encrypted Data packet. It is a new feature
* created for OpenPGP that addresses the problem of detecting a modification to
* encrypted data. It is used in combination with a Modification Detection Code
* packet.
* @requires crypto
* @requires util
* @module packet/sym_encrypted_integrity_protected
*/
module.exports = SymEncryptedIntegrityProtected;
var util = require('../util.js'),
crypto = require('../crypto');
/**
* @constructor
*/
function SymEncryptedIntegrityProtected() {
/** The encrypted payload. */
this.encrypted = null; // string
/**
* If after decrypting the packet this is set to true,
* a modification has been detected and thus the contents
* should be discarded.
* @type {Boolean}
*/
this.modification = false;
this.packets = null;
}
SymEncryptedIntegrityProtected.prototype.read = function (bytes) {
// - A one-octet version number. The only currently defined value is 1.
var version = bytes.charCodeAt(0);
if (version != 1) {
throw new Error('Invalid packet version.');
}
// - Encrypted data, the output of the selected symmetric-key cipher
// operating in Cipher Feedback mode with shift amount equal to the
// block size of the cipher (CFB-n where n is the block size).
this.encrypted = bytes.substr(1);
};
SymEncryptedIntegrityProtected.prototype.write = function () {
// 1 = Version
return String.fromCharCode(1) + this.encrypted;
};
SymEncryptedIntegrityProtected.prototype.encrypt = function (sessionKeyAlgorithm, key) {
var bytes = this.packets.write();
var prefixrandom = crypto.getPrefixRandom(sessionKeyAlgorithm);
var prefix = prefixrandom + prefixrandom.charAt(prefixrandom.length - 2) + prefixrandom.charAt(prefixrandom.length -
1);
var tohash = bytes;
// Modification detection code packet.
tohash += String.fromCharCode(0xD3);
tohash += String.fromCharCode(0x14);
tohash += crypto.hash.sha1(prefix + tohash);
this.encrypted = crypto.cfb.encrypt(prefixrandom,
sessionKeyAlgorithm, tohash, key, false).substring(0,
prefix.length + tohash.length);
};
/**
* Decrypts the encrypted data contained in this object read_packet must
* have been called before
*
* @param {module:enums.symmetric} sessionKeyAlgorithm
* The selected symmetric encryption algorithm to be used
* @param {String} key The key of cipher blocksize length to be used
* @return {String} The decrypted data of this packet
*/
SymEncryptedIntegrityProtected.prototype.decrypt = function (sessionKeyAlgorithm, key) {
var decrypted = crypto.cfb.decrypt(
sessionKeyAlgorithm, key, this.encrypted, false);
// there must be a modification detection code packet as the
// last packet and everything gets hashed except the hash itself
this.hash = crypto.hash.sha1(
crypto.cfb.mdc(sessionKeyAlgorithm, key, this.encrypted) + decrypted.substring(0, decrypted.length - 20));
var mdc = decrypted.substr(decrypted.length - 20, 20);
if (this.hash != mdc) {
throw new Error('Modification detected.');
} else
this.packets.read(decrypted.substr(0, decrypted.length - 22));
};
</code></pre>
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