94 lines
2.2 KiB
JavaScript
94 lines
2.2 KiB
JavaScript
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const Int64 = require("node-int64");
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let 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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let table;
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function generateTable() {
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const poly = 0xEDB88320;
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let 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++) 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) generateTable();
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if (ch.charCodeAt) ch = ch.charCodeAt(0);
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const l = (crc.readUInt32BE() >> 8) & 0xffffff;
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const r = table[(crc.readUInt32BE() ^ (ch >>> 0)) & 0xff];
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return (l ^ r) >>> 0;
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}
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function multiply(a, b) {
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const ah = (a >> 16) & 0xffff;
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const al = a & 0xffff;
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const bh = (b >> 16) & 0xffff;
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const bl = b & 0xffff;
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const high = (ah * bl + al * bh) & 0xffff;
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return ((high << 16) >>> 0) + al * bl;
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}
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function Decrypt() {
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if (!(this instanceof Decrypt)) return new Decrypt();
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this.key0 = Buffer.allocUnsafe(4);
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this.key1 = Buffer.allocUnsafe(4);
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this.key2 = Buffer.allocUnsafe(4);
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this.key0.writeUInt32BE(0x12345678, 0);
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this.key1.writeUInt32BE(0x23456789, 0);
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this.key2.writeUInt32BE(0x34567890, 0);
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}
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Decrypt.prototype.update = function (h) {
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this.key0.writeUInt32BE(crc(h, this.key0));
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this.key1.writeUInt32BE(
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((this.key0.readUInt32BE() & 0xff & 0xFFFFFFFF) +
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this.key1.readUInt32BE()) >>> 0
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);
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const x = new Int64(
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(multiply(this.key1.readUInt32BE(), 134775813) + 1) & 0xFFFFFFFF
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);
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const b = Buffer.alloc(8);
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x.copy(b, 0);
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b.copy(this.key1, 0, 4, 8);
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this.key2.writeUInt32BE(
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crc(((this.key1.readUInt32BE() >> 24) & 0xff) >>> 0, this.key2)
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);
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};
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Decrypt.prototype.decryptByte = function (c) {
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const k = (this.key2.readUInt32BE() | 2) >>> 0;
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c = c ^ ((multiply(k, (k ^ 1 >>> 0)) >> 8) & 0xff);
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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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const stream = Stream.Transform(),
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self = this;
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stream._transform = function (d, e, cb) {
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for (let 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;
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