Telegram DNS

telegram-dns

#!/usr/bin/env ruby
require 'base64'
require 'openssl'
require 'net/http'
require 'ipaddr'
require 'json'

def handle_response(body)
  raw = Base64.decode64(body)
  rsa_key = OpenSSL::PKey::RSA.new(File.read('public_key.pem'))
  rsa_plaintext = rsa_key.public_decrypt(raw, OpenSSL::PKey::RSA::NO_PADDING)
  aes_ciphertext = rsa_plaintext[32, 224]

  cipher = OpenSSL::Cipher.new('aes-256-cbc')
  cipher.key = rsa_plaintext[0, 32]
  cipher.iv = rsa_plaintext[16, 16]
  cipher.padding = 0
  raw_config = cipher.update(aes_ciphertext)
  raw_config << cipher.final

  # Check SHA-2 hash
  match = Digest::SHA256.digest(raw_config[0, 208])[0, 16] == raw_config[208, 16]
  unless match
    puts 'SHA-2 mismatch'
    return
  end
  puts 'SHA-2 digest is correct'

  data = raw_config.unpack('V*')
  # => Search for the vector of IP & ports
  # 'd997c3c5' => 'help.configSimple',
  # '1cb5c415' => 'vector'
  position = data.find_index { |value| value.to_s(16) == '1cb5c415' }
  length = data[position + 1]

  puts "Found a vector of #{length} IP addresses"
  tuples = data[position + 2, length * 2]
  (0..(tuples.length - 1)).step(2).each do |index|
    puts " * #{IPAddr.new(tuples[index], Socket::AF_INET)}:#{tuples[index + 1]}"
  end
end

def download(uri, host)
  req = Net::HTTP::Get.new(uri)
  req['Host'] = host
  req['User-Agent'] = 'Mozilla/5.0 (iPhone; CPU iPhone OS 10_0 like Mac OS X) AppleWebKit/602.1.38 (KHTML, like Gecko) Version/10.0 Mobile/14A5297c Safari/602.1'
  Net::HTTP.start(uri.hostname, uri.port, use_ssl: true) do |http|
    http.request(req)
  end
end

puts '****** Google DNS ******'
uri = URI("https://google.com/resolve?name=ap.stel.com&type=16")
json = JSON.parse(download(uri, 'dns.google.com').body)
answers = json['Answer'].map{ |a| a['data'] }.sort_by(&:size).reverse
handle_response(answers.join(''))

puts '****** Appspot ******'
uri = URI('https://dns-telegram.appspot.com')
handle_response(download(uri, 'dns-telegram.appspot.com').body)

# 403 Forbidden: implemented in TDLib but not on the server side ?
# puts '****** Microsoft ******'
# uri = URI('https://software-download.microsoft.com/prod/config.txt')
# puts download(uri, 'tcdnb.azureedge.net').body
# handle_response(download(uri, 'tcdnb.azureedge.net').body)

Telegram public RSA key:

-----BEGIN RSA PUBLIC KEY-----
MIIBCgKCAQEAyr+18Rex2ohtVy8sroGP
BwXD3DOoKCSpjDqYoXgCqB7ioln4eDCFfOBUlfXUEvM/fnKCpF46VkAftlb4VuPD
eQSS/ZxZYEGqHaywlroVnXHIjgqoxiAd192xRGreuXIaUKmkwlM9JID9WS2jUsTp
zQ91L8MEPLJ/4zrBwZua8W5fECwCCh2c9G5IzzBm+otMS/YKwmR1olzRCyEkyAEj
XWqBI9Ftv5eG8m0VkBzOG655WIYdyV0HfDK/NWcvGqa0w/nriMD6mDjKOryamw0O
P9QuYgMN0C9xMW9y8SmP4h92OAWodTYgY1hZCxdv6cs5UnW9+PWvS+WIbkh+GaWY
xwIDAQAB
-----END RSA PUBLIC KEY-----