class ROTP::OTP

Attributes

digest[R]
digits[R]
secret[R]

Public Class Methods

new(s, options = {}) click to toggle source

@param [String] secret in the form of base32 @option options digits [Integer] (6)

Number of integers in the OTP
Google Authenticate only supports 6 currently

@option options digest [String] (sha1)

Digest used in the HMAC
Google Authenticate only supports 'sha1' currently

@returns [OTP] OTP instantiation

# File lib/rotp/otp.rb, line 13
def initialize(s, options = {})
  @digits = options[:digits] || 6
  @digest = options[:digest] || "sha1"
  @secret = s
end

Public Instance Methods

generate_otp(input, padded=true) click to toggle source

@param [Integer] input the number used seed the HMAC @option padded [Boolean] (false) Output the otp as a 0 padded string Usually either the counter, or the computed integer based on the Unix timestamp

# File lib/rotp/otp.rb, line 23
def generate_otp(input, padded=true)
  hmac = OpenSSL::HMAC.digest(
    OpenSSL::Digest.new(digest),
    byte_secret,
    int_to_bytestring(input)
  )

  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

Private Instance Methods

byte_secret() click to toggle source
# File lib/rotp/otp.rb, line 51
def byte_secret
  Base32.decode(@secret)
end
encode_params(uri, params) click to toggle source

A very simple param encoder

# File lib/rotp/otp.rb, line 69
def encode_params(uri, params)
  params_str = String.new("?")
  params.each do |k,v|
    if v
      params_str << "#{k}=#{CGI::escape(v.to_s)}&"
    end
  end
  params_str.chop!
  uri + params_str
end
int_to_bytestring(int, padding = 8) click to toggle source

Turns an integer to the OATH specified bytestring, which is fed to the HMAC along with the secret

# File lib/rotp/otp.rb, line 59
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
time_constant_compare(a, b) click to toggle source

constant-time compare the strings

# File lib/rotp/otp.rb, line 81
def time_constant_compare(a, b)
  return false if a.empty? || b.empty? || a.bytesize != b.bytesize
  l = a.unpack "C#{a.bytesize}"
  res = 0
  b.each_byte { |byte| res |= byte ^ l.shift }
  res == 0
end
verify(input, generated) click to toggle source
# File lib/rotp/otp.rb, line 44
def verify(input, generated)
  unless input.is_a?(String) && generated.is_a?(String)
    raise ArgumentError, "ROTP only verifies strings - See: https://github.com/mdp/rotp/issues/32"
  end
  time_constant_compare(input, generated)
end