Ruby on Rails 5.1.6 Session Decryptor

rails_session_decryptor-5.rb

# @author longcat (Pichaya Morimoto)
# Tested on ruby 2.5.3 on rails 5.1.6 
# modded from https://gist.github.com/erose/36a514bc5ac9c5f18552369265b4d449
# $ gem install application_config
# $ gem install activesupport
require 'cgi'
require 'json'
require 'active_support'
require 'application_config'
# $ rails runner 'Rails.application.config.action_dispatch.tap { |c| p encrypted_cookie_salt: c.encrypted_cookie_salt, encrypted_signed_cookie_salt: c.encrypted_signed_cookie_salt }'
# {:encrypted_cookie_salt=>"encrypted cookie", :encrypted_signed_cookie_salt=>"signed encrypted cookie"}
# $ rails runner 'p Rails.application.secrets.secret_key_base'
# "2f1d90a26236c3245d96f5606c201a780dc9ca687e5ed82b45e211bb5dc84c1870f61ca9e002dad5dd8a149c9792d8f07f31a9575065cca064bd6af44f8750e4"
def verify_and_decrypt_session_cookie(cookie, secret_key_base)
  cookie = CGI::unescape(cookie)
  # salt = ApplicationConfig.get.action_dispatch.encrypted_cookie_salt
  # signed_salt = ApplicationConfig.get.action_dispatch.encrypted_signed_cookie_salt
  salt = "encrypted cookie"
  signed_salt = "signed encrypted cookie"
  key_generator = ActiveSupport::KeyGenerator.new(secret_key_base, iterations: 1000)
  secret = key_generator.generate_key(salt)[0, 32]
  sign_secret = key_generator.generate_key(signed_salt)
  # encryptor = ActiveSupport::MessageEncryptor.new(secret, sign_secret, serializer: JSON)
  encryptor = ActiveSupport::MessageEncryptor.new(secret, sign_secret, serializer: Marshal)

  encryptor.decrypt_and_verify(cookie)
end

puts verify_and_decrypt_session_cookie('K2x3aUNMc2h6Zk1McjRQKzMwZ0QwZnd0Y2JyazJqcDByWUhHL2JTb1hrSzRCWTYzV0piRjJ5YmYwWDQyQlEwWnVuNFBMSEpTang2dDdSVVJNZzJRZG5CczBtYXRUdXB1N3pOaVhQMk9SMUxYbE1kamFVVUpOdmZNNkR3M0p4VThoU3RuQit0MkdINlNpVkdPQk55NUh2R3NsbTFqT0NSSm03cDdCWFFEZHdxWklnd1B6MmxLenJFV1N6ZXplMHhocVhNRm1rUGRJQlpnclhSUWtzOTNUUT09LS1tSHROSmxsd3B6Nk1aMVpKb09ZcVdRPT0=--d468d168e3220510b0e21f16f67357c19c15677e','2f1d90a26236c3245d96f5606c201a780dc9ca687e5ed82b45e211bb5dc84c1870f61ca9e002dad5dd8a149c9792d8f07f31a9575065cca064bd6af44f8750e4')

# $ ruby rails_session_decryptor-5.rb
# {"session_id"=>"ebed7e1a3f559b8fc5d7df8ac71a782e", "_csrf_token"=>"OJpeV8IQToGcTf5KBTGqemrqSzeqTEyeUNQY5oFwWCk=", "user_id"=>8}