The Ruby One Time Password Library

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A ruby library for generating and validating one time passwords (HOTP & TOTP) according to RFC 4226 and RFC 6238.

ROTP is compatible with Google Authenticator available for Android and iPhone and any other TOTP based implementations.

Many websites use this for multi-factor authentication, such as GMail, Facebook, Amazon EC2, WordPress, and Salesforce. You can find a more complete list here.


  • OpenSSL
  • Ruby 2.0 or higher

Breaking changes

Breaking changes in >= 6.0

  • Dropping support for Ruby <2.3

Breaking changes in >= 5.0

  • ROTP::Base32.random_base32 is now ROTP::Base32.random and the argument has changed from secret string length to byte length to allow for more precision. There is an alias to allow for random_base32 for the time being.
  • Cleaned up the Base32 implementation to match Google Authenticator’s version.

Breaking changes in >= 4.0

  • Simplified API
    • verify now takes options for drift and after
    • verify returns a timestamp if true, nil if false
  • Dropping support for Ruby < 2.0
  • Docs for 3.x can be found here


bash gem install rotp

Library Usage

Time based OTP’s

```ruby totp =“base32secret3232”, issuer: “My Service”) # => “492039”

OTP verified for current time - returns timestamp of the current interval

# period. totp.verify(“492039”) # => 1474590700

sleep 30

OTP fails to verify - returns nil

totp.verify(“492039”) # => nil ```

Counter based OTP’s

```ruby hotp =“base32secretkey3232”) # => “786922” # => “595254” # => “259769”

OTP verified with a counter

hotp.verify(“259769”, 1401) # => 1401 hotp.verify(“259769”, 1402) # => nil ```

Preventing reuse of Time based OTP’s

By keeping track of the last time a user’s OTP was verified, we can prevent token reuse during the interval window (default 30 seconds)

The following is an example of this in action:

```ruby user = User.find(someUserID) totp = # => “492039”

Let’s take a look at the last time the user authenticated with an OTP

user.last_otp_at # => 1432703530

Verify the OTP

last_otp_at = totp.verify(“492039”, after: user.last_otp_at) #=> 1472145760 # ROTP returns the timestamp(int) of the current period

Store this on the user’s account

user.update(last_otp_at: last_otp_at)

Someone attempts to reuse the OTP inside the 30s window

last_otp_at = totp.verify(“492039”, after: user.last_otp_at) #=> nil # It fails to verify because we are still in the same 30s interval window ```

Verifying a Time based OTP with drift

Some users may enter a code just after it has expired. By adding ‘drift’ you can allow for a recently expired token to remain valid.

```ruby totp =“base32secret3232”) now = #2016-09-23 00:30:00 UTC # => “250939”

OTP verified for current time along with 15 seconds earlier

# ie. User enters a code just after it expired totp.verify(“250939”, drift_behind: 15, at: now + 35) # => 1474590600 # User waits too long. Fails to validate previous OTP totp.verify(“250939”, drift_behind: 15, at: now + 45) # => nil ```

Generating a Base32 Secret key

ruby ROTP::Base32.random # returns a 160 bit (32 character) base32 secret. Compatible with Google Authenticator

Note: The Base32 format conforms to RFC 4648 Base32

Generating QR Codes for provisioning mobile apps

Provisioning URI’s generated by ROTP are compatible with most One Time Password applications, including Google Authenticator.

```ruby totp =“base32secret3232”, issuer: “My Service”) totp.provisioning_uri(“[email protected]”) # => ‘otpauth://totp/’

hotp =“base32secret3232”, issuer: “My Service”) hotp.provisioning_uri(“[email protected]”, 0) # => ‘otpauth://hotp/’ ```

This can then be rendered as a QR Code which the user can scan using their mobile phone and the appropriate application.

Working example

Scan the following barcode with your phone, using Google Authenticator

QR Code for OTP

Now run the following and compare the output

ruby require 'rubygems' require 'rotp' totp ="JBSWY3DPEHPK3PXP") p "Current OTP: #{}"


bash bundle install bundle exec rspec

Testing with Docker

In order to make it easier to test against different ruby version, ROTP comes with a set of Dockerfiles for each version that we test against in Travis

bash docker build -f Dockerfile-2.6 -t rotp_2.6 . docker run --rm -v $(pwd):/usr/src/app rotp_2.6

Alternately, you may use docker-compose to run all the tests:

docker-compose up

Executable Usage

The rotp rubygem includes CLI version to help with testing and debugging

```bash # Try this to get an overview of the commands rotp –help


rotp –secret p4ssword # Generates a time-based one-time password rotp –hmac –secret p4ssword –counter 42 # Generates a counter-based one-time password ```


Have a look at the contributors graph on Github.


MIT Copyright (C) 2019 by Mark Percival, see LICENSE for details.

Other implementations

A list can be found at Wikipedia.