Rclone Deobscure function (Typescript/Javascript)

rclonedeobscure.ts

/*
  This is a function to decrypt (deobscure) rclone passwords
  Author: Danil Valov
  Original code: https://github.com/maaaaz/rclonedeobscure (Thomas D.)
 */

import crypto from 'crypto';

// AES-256-CBC always has a block size of 16 bytes
const AESBlockSize = 16;

// -- https://github.com/rclone/rclone/blob/master/fs/config/obscure/obscure.go
const secretKey = Buffer.from([
  0x9c, 0x93, 0x5b, 0x48, 0x73, 0x0a, 0x55, 0x4d, 0x6b, 0xfd, 0x7c, 0x63, 0xc8, 0x86, 0xa9, 0x2b, 0xd3, 0x90, 0x19,
  0x8e, 0xb8, 0x12, 0x8a, 0xfb, 0xf4, 0xde, 0x16, 0x2b, 0x8b, 0x95, 0xf6, 0x38,
]);

const base64Urlsafedecode = (string: string): Buffer => {
  const padding = 4 - (string.length % 4);

  return Buffer.from(string + '='.repeat(padding), 'base64');
};

const aesCtrEncrypt = (encryptedPassword: Buffer, iv: Buffer) => {
  const cipher = crypto.createDecipheriv('aes-256-ctr', secretKey, iv);

  return cipher.update(encryptedPassword, undefined, 'utf-8') + cipher.final('utf-8');
};

export default (obscured: string): string => {
  const encryptedPassword = base64Urlsafedecode(obscured);

  const buf = encryptedPassword.slice(AESBlockSize);
  const iv = encryptedPassword.slice(0, AESBlockSize);

  return aesCtrEncrypt(buf, iv);
};

sample.ts

import rcloneDeobscure from './rclonedeobscure.ts';

const obscuredString = '9NUHOyrjZZimLXZbNvOegwkdv9d1XQAwCsrKXxsl';
const deobscuredString = rcloneDeobscure(obscuredString);

console.log(deobscuredString); // "secretpassword"