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<h1 class="page-title">Source: packet/openpgp.packet.encryptedintegrityprotecteddata.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 Implementation of the Sym. Encrypted Integrity Protected Data
* Packet (Tag 18)
*
* 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.
*/
function openpgp_packet_encryptedintegrityprotecteddata() {
this.tagType = 18;
this.version = null; // integer == 1
this.packetLength = null; // integer
this.encryptedData = null; // string
this.decrytpedData = null; // string
this.hash = null; // string
/**
* Parsing function for the packet.
*
* @param {String} input Payload of a tag 18 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_encryptedintegrityprotecteddata} object
* representation
*/
function read_packet(input, position, len) {
this.packetLength = len;
// - A one-octet version number. The only currently defined value is
// 1.
this.version = input[position].charCodeAt();
if (this.version != 1) {
util
.print_error('openpgp.packet.encryptedintegrityprotecteddata.js\nunknown encrypted integrity protected data packet version: '
+ this.version
+ " , @ "
+ position
+ "hex:"
+ util.hexstrdump(input));
return null;
}
// - 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.encryptedData = input.substring(position + 1, position + 1 + len);
util.print_debug("openpgp.packet.encryptedintegrityprotecteddata.js\n"
+ this.toString());
return this;
}
/**
* Creates a string representation of a Sym. Encrypted Integrity Protected
* Data Packet (tag 18) (see RFC4880 5.13)
*
* @param {Integer} symmetric_algorithm
* The selected symmetric encryption algorithm to be used
* @param {String} key The key of cipher blocksize length to be used
* @param {String} data
* Plaintext data to be encrypted within the packet
* @return {String} A string representation of the packet
*/
function write_packet(symmetric_algorithm, key, data) {
var prefixrandom = openpgp_crypto_getPrefixRandom(symmetric_algorithm);
var prefix = prefixrandom
+ prefixrandom.charAt(prefixrandom.length - 2)
+ prefixrandom.charAt(prefixrandom.length - 1);
var tohash = data;
tohash += String.fromCharCode(0xD3);
tohash += String.fromCharCode(0x14);
util.print_debug_hexstr_dump("data to be hashed:"
, prefix + tohash);
tohash += str_sha1(prefix + tohash);
util.print_debug_hexstr_dump("hash:"
, tohash.substring(tohash.length - 20,
tohash.length));
var result = openpgp_crypto_symmetricEncrypt(prefixrandom,
symmetric_algorithm, key, tohash, false).substring(0,
prefix.length + tohash.length);
var header = openpgp_packet.write_packet_header(18, result.length + 1)
+ String.fromCharCode(1);
this.encryptedData = result;
return header + result;
}
/**
* Decrypts the encrypted data contained in this object read_packet must
* have been called before
*
* @param {Integer} symmetric_algorithm_type
* 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
*/
function decrypt(symmetric_algorithm_type, key) {
this.decryptedData = openpgp_crypto_symmetricDecrypt(
symmetric_algorithm_type, key, this.encryptedData, false);
// there must be a modification detection code packet as the
// last packet and everything gets hashed except the hash itself
this.hash = str_sha1(openpgp_crypto_MDCSystemBytes(
symmetric_algorithm_type, key, this.encryptedData)
+ this.decryptedData.substring(0,
this.decryptedData.length - 20));
util.print_debug_hexstr_dump("calc hash = ", this.hash);
if (this.hash == this.decryptedData.substring(
this.decryptedData.length - 20, this.decryptedData.length))
return this.decryptedData;
else
util
.print_error("Decryption stopped: discovered a modification of encrypted data.");
return null;
}
function toString() {
var data = '';
if(openpgp.config.debug)
data = ' data: Bytes ['
+ util.hexstrdump(this.encryptedData) + ']';
return '5.13. Sym. Encrypted Integrity Protected Data Packet (Tag 18)\n'
+ ' length: '
+ this.packetLength
+ '\n'
+ ' version: '
+ this.version
+ '\n'
+ data;
}
this.write_packet = write_packet;
this.read_packet = read_packet;
this.toString = toString;
this.decrypt = decrypt;
};
</code></pre>
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