homebridge-miot/lib/utils/CustomCryptRC4.js

Homebridge plugin for devices supporting the miot protocol

// based on: https://github.com/sipiyou/edomi-roboroc/blob/main/php/cryptRC4.php
// since nodejs v18.x.x, rc4 seems deaprecated? so for now lets use our own implementation

class CustomCryptRC4 {

  constructor(key, rounds) {
    this.setKey(key || '', rounds);
  }

  setKey(key, rounds) {
    let ksa = Array.from({
      length: 256
    }, (v, k) => k);
    let i = 0;
    let j = 0;

    if (key.length > 0) {
      key = Buffer.from(key);
      let len = key.length;

      for (i = 0; i < 256; i++) {
        j = (j + ksa[i] + key[i % len]) & 255;
        [ksa[i], ksa[j]] = [ksa[j], ksa[i]];
      }

      i = j = 0;

      for (let c = 0; c < rounds; c++) {
        i = (i + 1) & 255;
        j = (j + ksa[i]) & 255;
        [ksa[i], ksa[j]] = [ksa[j], ksa[i]];
      }
    }

    this._ksa = ksa;
    this._idx = i;
    this._jdx = j;
  }

  crypt(data) {
    let ksa = (this._ksa || []).slice(0); // Array copy
    let i = this._idx || 0;
    let j = this._jdx || 0;

    let len = data.length;
    let out = Buffer.alloc(len);

    for (let c = 0; c < len; c++) {
      i = (i + 1) & 255;
      j = (j + ksa[i]) & 255;
      [ksa[i], ksa[j]] = [ksa[j], ksa[i]];

      out[c] = data[c] ^ ksa[(ksa[i] + ksa[j]) & 255];
    }

    return out;
  }

  encode(data) {
    return this.crypt(Buffer.from(data, 'utf8')).toString('base64');
  }

  decode(data) {
    return this.crypt(Buffer.from(data, 'base64')).toString('utf8');
  }

  static create(key, rounds) {
    return new CustomCryptRC4(key, rounds);
  }

}

module.exports = CustomCryptRC4;