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<h1 class="page-title">Source: type/s2k.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 String-to-key specifier (RFC4880 3.7)<br/>
* <br/>
* String-to-key (S2K) specifiers are used to convert passphrase strings
* into symmetric-key encryption/decryption keys. They are used in two
* places, currently: to encrypt the secret part of private keys in the
* private keyring, and to convert passphrases to encryption keys for
* symmetrically encrypted messages.
* @requires crypto
* @requires enums
* @requires util
* @module type/s2k
*/
var enums = require('../enums.js'),
util = require('../util'),
crypto = require('../crypto');
/**
* @constructor
*/
module.exports = function s2k() {
/** @type {module:enums.hash} */
this.algorithm = 'sha256';
/** @type {module:enums.s2k} */
this.type = 'iterated';
this.c = 96;
/** Eight bytes of salt in a binary string.
* @type {String}
*/
this.salt = crypto.random.getRandomBytes(8);
// Exponent bias, defined in RFC4880
var expbias = 6;
this.get_count = function () {
return (16 + (this.c & 15)) << ((this.c >> 4) + expbias);
};
/**
* Parsing function for a string-to-key specifier (RFC 4880 3.7).
* @param {String} input Payload of string-to-key specifier
* @return {Integer} Actual length of the object
*/
this.read = function (bytes) {
var i = 0;
this.type = enums.read(enums.s2k, bytes.charCodeAt(i++));
this.algorithm = enums.read(enums.hash, bytes.charCodeAt(i++));
switch (this.type) {
case 'simple':
break;
case 'salted':
this.salt = bytes.substr(i, 8);
i += 8;
break;
case 'iterated':
this.salt = bytes.substr(i, 8);
i += 8;
// Octet 10: count, a one-octet, coded value
this.c = bytes.charCodeAt(i++);
break;
case 'gnu':
if (bytes.substr(i, 3) == "GNU") {
i += 3; // GNU
var gnuExtType = 1000 + bytes.charCodeAt(i++);
if (gnuExtType == 1001) {
this.type = gnuExtType;
// GnuPG extension mode 1001 -- don't write secret key at all
} else {
throw new Error("Unknown s2k gnu protection mode.");
}
} else {
throw new Error("Unknown s2k type.");
}
break;
default:
throw new Error("Unknown s2k type.");
break;
}
return i;
};
/**
* writes an s2k hash based on the inputs.
* @return {String} Produced key of hashAlgorithm hash length
*/
this.write = function () {
var bytes = String.fromCharCode(enums.write(enums.s2k, this.type));
bytes += String.fromCharCode(enums.write(enums.hash, this.algorithm));
switch (this.type) {
case 'simple':
break;
case 'salted':
bytes += this.salt;
break;
case 'iterated':
bytes += this.salt;
bytes += String.fromCharCode(this.c);
break;
}
return bytes;
};
/**
* Produces a key using the specified passphrase and the defined
* hashAlgorithm
* @param {String} passphrase Passphrase containing user input
* @return {String} Produced key with a length corresponding to
* hashAlgorithm hash length
*/
this.produce_key = function (passphrase, numBytes) {
passphrase = util.encode_utf8(passphrase);
function round(prefix, s2k) {
var algorithm = enums.write(enums.hash, s2k.algorithm);
switch (s2k.type) {
case 'simple':
return crypto.hash.digest(algorithm, prefix + passphrase);
case 'salted':
return crypto.hash.digest(algorithm,
prefix + s2k.salt + passphrase);
case 'iterated':
var isp = [],
count = s2k.get_count();
data = s2k.salt + passphrase;
while (isp.length * data.length < count)
isp.push(data);
isp = isp.join('');
if (isp.length > count)
isp = isp.substr(0, count);
return crypto.hash.digest(algorithm, prefix + isp);
}
}
var result = '',
prefix = '';
while (result.length <= numBytes) {
result += round(prefix, this);
prefix += String.fromCharCode(0);
}
return result.substr(0, numBytes);
};
};
</code></pre>
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