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/**
* Javascript implementation of mask generation function MGF1.
*
* @author Stefan Siegl
* @author Dave Longley
*
* Copyright (c) 2012 Stefan Siegl <stesie@brokenpipe.de>
* Copyright (c) 2014 Digital Bazaar, Inc.
*/
var forge = require('./forge');
require('./util');
forge.mgf = forge.mgf || {};
var mgf1 = module.exports = forge.mgf.mgf1 = forge.mgf1 = forge.mgf1 || {};
/**
* Creates a MGF1 mask generation function object.
*
* @param md the message digest API to use (eg: forge.md.sha1.create()).
*
* @return a mask generation function object.
*/
mgf1.create = function(md) {
var mgf = {
/**
* Generate mask of specified length.
*
* @param {String} seed The seed for mask generation.
* @param maskLen Number of bytes to generate.
* @return {String} The generated mask.
*/
generate: function(seed, maskLen) {
/* 2. Let T be the empty octet string. */
var t = new forge.util.ByteBuffer();
/* 3. For counter from 0 to ceil(maskLen / hLen), do the following: */
var len = Math.ceil(maskLen / md.digestLength);
for(var i = 0; i < len; i++) {
/* a. Convert counter to an octet string C of length 4 octets */
var c = new forge.util.ByteBuffer();
c.putInt32(i);
/* b. Concatenate the hash of the seed mgfSeed and C to the octet
* string T: */
md.start();
md.update(seed + c.getBytes());
t.putBuffer(md.digest());
}
/* Output the leading maskLen octets of T as the octet string mask. */
t.truncate(t.length() - maskLen);
return t.getBytes();
}
};
return mgf;
};