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<h1 class="page-title">Source: packet/sym_encrypted_session_key.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
/**
* Public-Key Encrypted Session Key Packets (Tag 1)<br/>
* <br/>
* RFC4880 5.1: A Public-Key Encrypted Session Key packet holds the session key
* used to encrypt a message. Zero or more Public-Key Encrypted Session Key
* packets and/or Symmetric-Key Encrypted Session Key packets may precede a
* Symmetrically Encrypted Data Packet, which holds an encrypted message. The
* message is encrypted with the session key, and the session key is itself
* encrypted and stored in the Encrypted Session Key packet(s). The
* Symmetrically Encrypted Data Packet is preceded by one Public-Key Encrypted
* Session Key packet for each OpenPGP key to which the message is encrypted.
* The recipient of the message finds a session key that is encrypted to their
* public key, decrypts the session key, and then uses the session key to
* decrypt the message.
* @requires crypto
* @requires enums
* @requires type/s2k
* @module packet/sym_encrypted_session_key
*/
var type_s2k = require('../type/s2k.js'),
enums = require('../enums.js'),
crypto = require('../crypto');
module.exports = SymEncryptedSessionKey;
/**
* @constructor
*/
function SymEncryptedSessionKey() {
this.tag = 3;
this.sessionKeyEncryptionAlgorithm = null;
this.sessionKeyAlgorithm = 'aes256';
this.encrypted = null;
this.s2k = new type_s2k();
}
/**
* Parsing function for a symmetric encrypted session key packet (tag 3).
*
* @param {String} input Payload of a tag 1 packet
* @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:packet/sym_encrypted_session_key} Object representation
*/
SymEncryptedSessionKey.prototype.read = function(bytes) {
// A one-octet version number. The only currently defined version is 4.
this.version = bytes.charCodeAt(0);
// A one-octet number describing the symmetric algorithm used.
var algo = enums.read(enums.symmetric, bytes.charCodeAt(1));
// A string-to-key (S2K) specifier, length as defined above.
var s2klength = this.s2k.read(bytes.substr(2));
// Optionally, the encrypted session key itself, which is decrypted
// with the string-to-key object.
var done = s2klength + 2;
if (done < bytes.length) {
this.encrypted = bytes.substr(done);
this.sessionKeyEncryptionAlgorithm = algo;
} else
this.sessionKeyAlgorithm = algo;
};
SymEncryptedSessionKey.prototype.write = function() {
var algo = this.encrypted === null ?
this.sessionKeyAlgorithm :
this.sessionKeyEncryptionAlgorithm;
var bytes = String.fromCharCode(this.version) +
String.fromCharCode(enums.write(enums.symmetric, algo)) +
this.s2k.write();
if (this.encrypted !== null)
bytes += this.encrypted;
return bytes;
};
/**
* Decrypts the session key (only for public key encrypted session key
* packets (tag 1)
*
* @return {String} The unencrypted session key
*/
SymEncryptedSessionKey.prototype.decrypt = function(passphrase) {
var algo = this.sessionKeyEncryptionAlgorithm !== null ?
this.sessionKeyEncryptionAlgorithm :
this.sessionKeyAlgorithm;
var length = crypto.cipher[algo].keySize;
var key = this.s2k.produce_key(passphrase, length);
if (this.encrypted === null) {
this.sessionKey = key;
} else {
var decrypted = crypto.cfb.decrypt(
this.sessionKeyEncryptionAlgorithm, key, this.encrypted, true);
this.sessionKeyAlgorithm = enums.read(enums.symmetric,
decrypted[0].keyCodeAt());
this.sessionKey = decrypted.substr(1);
}
};
SymEncryptedSessionKey.prototype.encrypt = function(passphrase) {
var length = crypto.getKeyLength(this.sessionKeyEncryptionAlgorithm);
var key = this.s2k.produce_key(passphrase, length);
var private_key = String.fromCharCode(
enums.write(enums.symmetric, this.sessionKeyAlgorithm)) +
crypto.getRandomBytes(
crypto.getKeyLength(this.sessionKeyAlgorithm));
this.encrypted = crypto.cfb.encrypt(
crypto.getPrefixRandom(this.sessionKeyEncryptionAlgorithm),
this.sessionKeyEncryptionAlgorithm, key, private_key, true);
};
</code></pre>
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