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<h1 class="page-title">Source: packet/openpgp.packet.encryptedsessionkey.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
/**
* @class
* @classdesc Public-Key Encrypted Session Key Packets (Tag 1)
*
* 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.
*/
function openpgp_packet_encryptedsessionkey() {
/**
* Parsing function for a publickey encrypted session key packet (tag 1).
*
* @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 {openpgp_packet_encrypteddata} Object representation
*/
function read_pub_key_packet(input, position, len) {
this.tagType = 1;
this.packetLength = len;
var mypos = position;
if (len < 10) {
util
.print_error("openpgp.packet.encryptedsessionkey.js\n" + 'invalid length');
return null;
}
this.version = input[mypos++].charCodeAt();
this.keyId = new openpgp_type_keyid();
this.keyId.read_packet(input, mypos);
mypos += 8;
this.publicKeyAlgorithmUsed = input[mypos++].charCodeAt();
switch (this.publicKeyAlgorithmUsed) {
case 1:
case 2: // RSA
this.MPIs = new Array();
this.MPIs[0] = new openpgp_type_mpi();
this.MPIs[0].read(input, mypos, mypos - position);
break;
case 16: // Elgamal
this.MPIs = new Array();
this.MPIs[0] = new openpgp_type_mpi();
this.MPIs[0].read(input, mypos, mypos - position);
mypos += this.MPIs[0].packetLength;
this.MPIs[1] = new openpgp_type_mpi();
this.MPIs[1].read(input, mypos, mypos - position);
break;
default:
util.print_error("openpgp.packet.encryptedsessionkey.js\n"
+ "unknown public key packet algorithm type "
+ this.publicKeyAlgorithmType);
break;
}
return this;
}
/**
* Create a string representation of a tag 1 packet
*
* @param {String} publicKeyId
* The public key id corresponding to publicMPIs key as string
* @param {openpgp_type_mpi[]} publicMPIs
* Multiprecision integer objects describing the public key
* @param {Integer} pubalgo
* The corresponding public key algorithm // See RFC4880 9.1
* @param {Integer} symmalgo
* The symmetric cipher algorithm used to encrypt the data
* within an encrypteddatapacket or encryptedintegrity-
* protecteddatapacket
* following this packet //See RFC4880 9.2
* @param {String} sessionkey
* A string of randombytes representing the session key
* @return {String} The string representation
*/
function write_pub_key_packet(publicKeyId, publicMPIs, pubalgo, symmalgo,
sessionkey) {
var result = String.fromCharCode(3);
var data = String.fromCharCode(symmalgo);
data += sessionkey;
var checksum = util.calc_checksum(sessionkey);
data += String.fromCharCode((checksum >> 8) & 0xFF);
data += String.fromCharCode((checksum) & 0xFF);
result += publicKeyId;
result += String.fromCharCode(pubalgo);
var mpi = new openpgp_type_mpi();
var mpiresult = openpgp_crypto_asymetricEncrypt(pubalgo, publicMPIs,
mpi.create(openpgp_encoding_eme_pkcs1_encode(data,
publicMPIs[0].mpiByteLength)));
for ( var i = 0; i < mpiresult.length; i++) {
result += mpiresult[i];
}
result = openpgp_packet.write_packet_header(1, result.length) + result;
return result;
}
/**
* 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 {openpgp_packet_encrypteddata} Object representation
*/
function read_symmetric_key_packet(input, position, len) {
this.tagType = 3;
var mypos = position;
// A one-octet version number. The only currently defined version is 4.
this.version = input[mypos++];
// A one-octet number describing the symmetric algorithm used.
this.symmetricKeyAlgorithmUsed = input[mypos++];
// A string-to-key (S2K) specifier, length as defined above.
this.s2k = new openpgp_type_s2k();
this.s2k.read(input, mypos);
// Optionally, the encrypted session key itself, which is decrypted
// with the string-to-key object.
if ((s2k.s2kLength + mypos) < len) {
this.encryptedSessionKey = new Array();
for ( var i = (mypos - position); i < len; i++) {
this.encryptedSessionKey[i] = input[mypos++];
}
}
return this;
}
/**
* Decrypts the session key (only for public key encrypted session key
* packets (tag 1)
*
* @param {openpgp_msg_message} msg
* The message object (with member encryptedData
* @param {openpgp_msg_privatekey} key
* Private key with secMPIs unlocked
* @return {String} The unencrypted session key
*/
function decrypt(msg, key) {
if (this.tagType == 1) {
var result = openpgp_crypto_asymetricDecrypt(
this.publicKeyAlgorithmUsed, key.publicKey.MPIs,
key.secMPIs, this.MPIs).toMPI();
var checksum = ((result.charCodeAt(result.length - 2) << 8) + result
.charCodeAt(result.length - 1));
var decoded = openpgp_encoding_eme_pkcs1_decode(result.substring(2, result.length - 2), key.publicKey.MPIs[0].getByteLength());
var sesskey = decoded.substring(1);
var algo = decoded.charCodeAt(0);
if (msg.encryptedData.tagType == 18)
return msg.encryptedData.decrypt(algo, sesskey);
else
return msg.encryptedData.decrypt_sym(algo, sesskey);
} else if (this.tagType == 3) {
util
.print_error("Symmetric encrypted sessionkey is not supported!");
return null;
}
}
/**
* Creates a string representation of this object (useful for debug
* purposes)
*
* @return {String} The string containing a openpgp description
*/
function toString() {
if (this.tagType == 1) {
var result = '5.1. Public-Key Encrypted Session Key Packets (Tag 1)\n'
+ ' KeyId: '
+ this.keyId.toString()
+ '\n'
+ ' length: '
+ this.packetLength
+ '\n'
+ ' version:'
+ this.version
+ '\n'
+ ' pubAlgUs:'
+ this.publicKeyAlgorithmUsed + '\n';
for ( var i = 0; i < this.MPIs.length; i++) {
result += this.MPIs[i].toString();
}
return result;
} else
return '5.3 Symmetric-Key Encrypted Session Key Packets (Tag 3)\n'
+ ' KeyId: ' + this.keyId.toString() + '\n'
+ ' length: ' + this.packetLength + '\n'
+ ' version:' + this.version + '\n' + ' symKeyA:'
+ this.symmetricKeyAlgorithmUsed + '\n' + ' s2k: '
+ this.s2k + '\n';
}
this.read_pub_key_packet = read_pub_key_packet;
this.read_symmetric_key_packet = read_symmetric_key_packet;
this.write_pub_key_packet = write_pub_key_packet;
this.toString = toString;
this.decrypt = decrypt;
};
</code></pre>
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