Generating One-Time Password using both HOTP and TOTP

hotp_plus_totp.rb

# encoding: utf-8
 
require 'openssl'
require "base64"
 
# https://github.com/mdp/rotp
require 'rotp'

 
def truncate_hmac(hmac, padded=true)
  digits = 6
  offset = hmac[-1].ord & 0xf
  code = (hmac[offset].ord & 0x7f) << 24 |
    (hmac[offset + 1].ord & 0xff) << 16 |
    (hmac[offset + 2].ord & 0xff) << 8 |
    (hmac[offset + 3].ord & 0xff)
  if padded
    (code % 10 ** digits).to_s.rjust(digits, '0')
  else
    code % 10 ** digits
  end
end

def int_to_bytestring(int, padding = 8)
  result = []
  until int == 0
    result << (int & 0xFF).chr
    int >>=  8
  end
  result.reverse.join.rjust(padding, 0.chr)
end
 
def hotp_plus_totp
  key = "JCAYAA4U23D7V2EC"
  counter = 0
  
  current_time = 1385472664
  time_index = current_time / 30
  
  counter_byte_array = int_to_bytestring(counter)
  time_byte_array = int_to_bytestring(time_index)
 
  base32_decoded_key = ROTP::Base32.decode(key)
 
  hmac = OpenSSL::HMAC.digest(OpenSSL::Digest::Digest.new('sha1'), base32_decoded_key, counter_byte_array)
  hmac2 = OpenSSL::HMAC.digest(OpenSSL::Digest::Digest.new('sha1'), hmac, time_byte_array)
 
  return "HOTP+TOTP: #{truncate_hmac(hmac2)} - Time index: #{time_index} - Counter: #{counter}"
end
 
puts hotp_plus_totp