# 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](http://tools.ietf.org/html/rfc4226) and [RFC 6238](http://tools.ietf.org/html/rfc6238).

ROTP is compatible with [Google Authenticator](https://github.com/google/google-authenticator) available for [Android](https://play.google.com/store/apps/details?id=com.google.android.apps.authenticator2) and [iPhone](https://itunes.apple.com/en/app/google-authenticator/id388497605) and any other TOTP based implementations.

Many websites use this for [multi-factor authentication](https://www.youtube.com/watch?v=17rykTIX_HY), such as GMail, Facebook, Amazon EC2, WordPress, and Salesforce. You can find a more complete [list here](https://en.wikipedia.org/wiki/Google_Authenticator#Usage).

## Dependencies

* OpenSSL
* Ruby 2.0 or higher

## 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](https://github.com/mdp/rotp/tree/v3.x)

## Installation

```bash
gem install rotp
```

## Library Usage

### Time based OTP's

```ruby
totp = ROTP::TOTP.new("base32secret3232", issuer: "My Service")
totp.now # => "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 = ROTP::HOTP.new("base32secretkey3232")
hotp.at(0) # => "786922"
hotp.at(1) # => "595254"
hotp.at(1401) # => "259769"

# OTP verified with a counter
hotp.verify("316439", 1401) # => 1401
hotp.verify("316439", 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.find(someUserID)
totp = ROTP::TOTP.new(user.otp_secret)
totp.now # => "492039"

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 reused 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 = ROTP::TOTP.new("base32secret3232")
now = Time.at(1474590600) #2016-09-23 00:30:00 UTC
totp.at(now) # => "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_base32  # returns a 32 character base32 secret. Compatible with Google Authenticator
```

Note: The Base32 format conforms to [RFC 4648 Base32](http://en.wikipedia.org/wiki/Base32#RFC_4648_Base32_alphabet)

### 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.provisioning_uri("alice@google.com") # => 'otpauth://totp/issuer:alice@google.com?secret=JBSWY3DPEHPK3PXP'
hotp.provisioning_uri("alice@google.com", 0) # => 'otpauth://hotp/issuer:alice@google.com?secret=JBSWY3DPEHPK3PXP&counter=0'
```

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](https://cloud.githubusercontent.com/assets/2868/18771262/54f109dc-80f2-11e6-863f-d2be62ee587a.png)

Now run the following and compare the output

```ruby
require 'rubygems'
require 'rotp'
totp = ROTP::TOTP.new("JBSWY3DPEHPK3PXP")
p "Current OTP: #{totp.now}"
```

### Testing

```bash
bundle install
bundle exec rspec
```

## Executable Usage

The rotp rubygem includes an executable for helping with testing and debugging

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

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

## Contributors

Have a look at the [contributors graph](https://github.com/mdp/rotp/graphs/contributors) on Github.

## License

MIT Copyright (C) 2016 by Mark Percival, see [LICENSE](https://github.com/mdp/rotp/blob/master/LICENSE) for details.

## Other implementations

A list can be found at [Wikipedia](https://en.wikipedia.org/wiki/Google_Authenticator#Implementations).