OTP

otp.rb

#!/usr/bin/env ruby

require 'base32'
require 'openssl'
require 'uri'

TOTP_INTERVAL = 30

def get_pasword(secret_key, t)
  now = t / TOTP_INTERVAL
  key = Base32.decode secret_key
  sha = OpenSSL::Digest::Digest.new('sha1')

  bytes = [ now ].pack('>q').reverse
  hmac = OpenSSL::HMAC.digest(sha, key.to_s, bytes)
  offset = nil
  if RUBY_VERSION > '1.9'
    offset = hmac[-1].ord & 0x0F
  else
    offset = hmac[-1] & 0x0F
  end
  hash = hmac[offset...offset + 4]

  code = hash.reverse.unpack('L')[0]
  code &= 0x7FFFFFFF
  code %= 1000000
end

accounts = []

# Read ~/.otp file line by line.
# e.g. otpauth://totp/user@localhost?secret=SECRET
File.open(File.join(Dir.home(), '.otp')).each do |line|
  uri = URI.parse(line)
  accounts << {
    :user => uri.path,
    :secret => URI.decode_www_form(uri.query).assoc('secret').last.upcase
  }
end

accounts.each {|account|
  now = Time.now
  current = get_pasword(account[:secret], now.to_i)
  puts "%s, %06d, %02ds" % [account[:user], current, TOTP_INTERVAL - (now.to_i % TOTP_INTERVAL)]
}