unzipper-esm/lib/Decrypt.js

Unzip cross-platform streaming API

import Int64 from "node-int64";
import { Transform } from "stream"; // "node:stream"

export default class Decrypt {
  constructor() {
    this.key0 = Buffer.allocUnsafe(4);
    this.key1 = Buffer.allocUnsafe(4);
    this.key2 = Buffer.allocUnsafe(4);

    this.key0.writeUInt32BE(0x12345678, 0);
    this.key1.writeUInt32BE(0x23456789, 0);
    this.key2.writeUInt32BE(0x34567890, 0);
  }

  update(h) {
    this.key0.writeUInt32BE(crc(h, this.key0));
    this.key1.writeUInt32BE(
      ((this.key0.readUInt32BE() & 0xff & 0xFFFFFFFF) +
        this.key1.readUInt32BE()) >>> 0
    );
    const x = new Int64(
      (multiply(this.key1.readUInt32BE(), 134775813) + 1) & 0xFFFFFFFF
    );
    const b = Buffer.alloc(8);
    x.copy(b, 0);
    b.copy(this.key1, 0, 4, 8);
    this.key2.writeUInt32BE(
      crc(((this.key1.readUInt32BE() >> 24) & 0xff) >>> 0, this.key2)
    );
  };

  decryptByte(c) {
    const k = (this.key2.readUInt32BE() | 2) >>> 0;
    c = c ^ ((multiply(k, (k ^ 1 >>> 0)) >> 8) & 0xff);
    this.update(c);

    return c;
  };

  stream() {
    const self = this;
    return new Transform({
      transform: function (d, e, cb) {
        for (let i = 0; i < d.length; i++) {
          d[i] = self.decryptByte(d[i]);
        }
        this.push(d);
        cb();
      }
    });
  };
}

let table;

function generateTable() {
  const poly = 0xEDB88320;
  let c, n, k;
  table = [];
  for (n = 0; n < 256; n++) {
    c = n;
    for (k = 0; k < 8; k++) c = c & 1 ? poly ^ (c >>> 1) : (c = c >>> 1);
    table[n] = c >>> 0;
  }
}

function crc(ch, crc) {
  if (!table) generateTable();

  if (ch.charCodeAt) ch = ch.charCodeAt(0);

  const l = (crc.readUInt32BE() >> 8) & 0xffffff;
  const r = table[(crc.readUInt32BE() ^ (ch >>> 0)) & 0xff];

  return (l ^ r) >>> 0;
}

function multiply(a, b) {
  const ah = (a >> 16) & 0xffff;
  const al = a & 0xffff;
  const bh = (b >> 16) & 0xffff;
  const bl = b & 0xffff;
  const high = (ah * bl + al * bh) & 0xffff;

  return ((high << 16) >>> 0) + al * bl;
}