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72 lines
1.6 KiB
72 lines
1.6 KiB
var bigInt = require('big-integer');
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var Stream = require('stream');
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// Backwards compatibility for node versions < 8
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if (!Stream.Writable || !Stream.Writable.prototype.destroy)
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Stream = require('readable-stream');
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var table;
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function generateTable() {
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var poly = 0xEDB88320,c,n,k;
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table = [];
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for (n = 0; n < 256; n++) {
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c = n;
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for (k = 0; k < 8; k++)
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c = (c & 1) ? poly ^ (c >>> 1) : c = c >>> 1;
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table[n] = c >>> 0;
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}
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}
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function crc(ch,crc) {
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if (!table)
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generateTable();
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if (ch.charCodeAt)
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ch = ch.charCodeAt(0);
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return (bigInt(crc).shiftRight(8).and(0xffffff)).xor(table[bigInt(crc).xor(ch).and(0xff)]).value;
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}
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function Decrypt() {
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if (!(this instanceof Decrypt))
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return new Decrypt();
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this.key0 = 305419896;
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this.key1 = 591751049;
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this.key2 = 878082192;
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}
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Decrypt.prototype.update = function(h) {
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this.key0 = crc(h,this.key0);
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this.key1 = bigInt(this.key0).and(255).and(4294967295).add(this.key1)
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this.key1 = bigInt(this.key1).multiply(134775813).add(1).and(4294967295).value;
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this.key2 = crc(bigInt(this.key1).shiftRight(24).and(255), this.key2);
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}
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Decrypt.prototype.decryptByte = function(c) {
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var k = bigInt(this.key2).or(2);
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c = c ^ bigInt(k).multiply(bigInt(k^1)).shiftRight(8).and(255);
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this.update(c);
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return c;
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};
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Decrypt.prototype.stream = function() {
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var stream = Stream.Transform(),
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self = this;
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stream._transform = function(d,e,cb) {
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for (var i = 0; i<d.length;i++) {
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d[i] = self.decryptByte(d[i]);
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}
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this.push(d);
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cb();
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};
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return stream;
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};
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module.exports = Decrypt; |