CoronaPresenceTracing

This Ruby gem helps you create QR codes and URLs which can be used with COVID-19 contact tracing apps such as the German Corona-Warn-App to check in at events or locations.

The concept of Decentralized Privacy-Preserving Presence Tracing is implemented and referred to as Event Registration in the Corona-Warn-App. Its implementation as described here is comparable to the CrowdNotifier proposal.

Add this gem to your Gemfile and run bundle install:

gem 'corona_presence_tracing'

Or install it yourself:

$ gem install corona_presence_tracing

First create a CWACheckIn instance with attributes that describe your venue or event. The following is an example for a retail store:

check_in = CoronaPresenceTracing::CWACheckIn.new(
  description: 'Grocery Store', # max. 100 characters
  address: 'Berlin', # max. 100 characters
  start_time: Time.new(2021, 5, 11, 7, 0), # or a Date or DateTime
  end_time: Time.new(2021, 5, 11, 22, 0), # or a Date or DateTime
  location_type: :permanent_retail, # see below for a list of types
  default_check_in_length: 30 # in minutes, optional for temporary events
)

The values you provide are validated and a CoronaPresenceTracing::ValidationError will be raised if any of them don't meet the constraints.

These are all possible location types:

You can now either get just the encoded payload or the full check-in URL:

check_in.encoded_payload
# CAESJQgBEg1Hcm9jZXJ5IF...
check_in.url
# https://e.coronawarn.app?v=1#CAESJQgBEg1Hcm9jZXJ5IF...

You can easily create check-in QR codes using RQRCode. Just use the URL of a check-in as the payload for the QR code:

check_in = CoronaPresenceTracing::CWACheckIn.new(...)
qr = RQRCode::QRCode.new(check_in.url)
svg = qr.as_svg

You can also decode an already encoded check-in payload to read its attributes:

# with a URL
check_in = CoronaPresenceTracing::CWACheckIn.decode('https://e.coronawarn.app?v=1#CAESJQgBEg...')
# or with just the encoded payload
check_in = CoronaPresenceTracing::CWACheckIn.decode('CAESJQgBEg...')
check_in.description # Grocery Store
check_in.start_time # 2021-05-11 07:00:00

Please be aware that if you re-encode these instances you will get a different result as the cryptographic seed inside the payload will not be copied over to the new CWACheckIn instance.

The check-in payload is designed to support apps from other countries as well. Currently no other apps seem to have implemented it, though. New classes next to CWACheckIn with app-specific attributes will be added as soon as this changes.

This gem is available as open source under the terms of the MIT License.