Decode a Vaccine Passport QR code and Display Contents

passport_time.rb

#!/usr/bin/env ruby

require 'base64'
require 'json'
require 'zlib'

# Requirements:
# Debian: apt-get install zbar-tools
# OSX: brew install zbar

class DecodePassport
  Result = Struct.new(:header, :passport, :signature)

  def self.call(filename)
    new.call(filename)
  end

  def call(filename)
    header, payload, signature = decode_jws(decode_shc(decode_qr(filename)))
    Result.new(
      JSON.parse(header),
      JSON.parse(deflate_payload(payload)),
      signature.bytes.map { |b| '%02x' % b }.join
    )
  end

  private

  def decode_qr(filename)
    `zbarimg --raw "#{filename}" 2>/dev/null`.tap do
      fail('Failed to decode QR') unless $?.success?
    end
  end

  def decode_shc(shc)
    shc.scan(/\d{2}/).map { |digit| (digit.to_i + 45).chr }.join
  end

  def decode_jws(jws)
    jws.split('.').map { |part| Base64.urlsafe_decode64(part) }
  end

  def deflate_payload(payload)
    Zlib::Inflate.new(-15).inflate(payload)
  end
end

if ARGV.size.zero?
  STDERR.puts("Usage: #{$0} <imagefile>")
  exit(1)
end
result = DecodePassport.call(ARGV.first)

puts 'Header:'
puts JSON.pretty_generate(result.header)

puts 'Signature:'
puts result.signature

puts 'Passport:'
puts JSON.pretty_generate(result.passport)