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