Don't encrypt the OTP secret

It doesn't add any security to have this encrypted, but it adds
complexity for podmins, because they need to backup the key.

closes #8014

.gitignore

@@ -11,7 +11,6 @@ app/assets/images/custom/
 # Configuration files
 config/diaspora.yml
 config/initializers/secret_token.rb
-config/initializers/twofa_encryption_key.rb 
 .bundle
 vendor/bundle/
 vendor/cache/

app/models/user.rb

@@ -19,11 +19,10 @@ class User < ApplicationRecord
   scope :halfyear_actives, ->(time = Time.now) { logged_in_since(time - 6.month) }
   scope :active, -> { joins(:person).where(people: {closed_account: false}) }
 
-  attribute :otp_secret
+  attr_encrypted :otp_secret, if: false, prefix: "plain_"
 
   devise :two_factor_authenticatable,
          :two_factor_backupable,
-         otp_secret_encryption_key:  AppConfig.twofa_encryption_key,
          otp_backup_code_length:     16,
          otp_number_of_backup_codes: 10
 

db/migrate/20171229175654_add_devise_two_factor_to_users.rb

@@ -2,10 +2,12 @@
 
 class AddDeviseTwoFactorToUsers < ActiveRecord::Migration[5.1]
   def change
-    add_column :users, :encrypted_otp_secret, :string
-    add_column :users, :encrypted_otp_secret_iv, :string
-    add_column :users, :encrypted_otp_secret_salt, :string
-    add_column :users, :consumed_timestep, :integer
-    add_column :users, :otp_required_for_login, :boolean
+    change_table :users, bulk: true do |t|
+      t.string :encrypted_otp_secret
+      t.string :encrypted_otp_secret_iv
+      t.string :encrypted_otp_secret_salt
+      t.integer :consumed_timestep
+      t.boolean :otp_required_for_login
+    end
   end
 end

db/migrate/20190511150503_decrypt_two_factor_secret.rb

+# frozen_string_literal: true
+
+class DecryptTwoFactorSecret < ActiveRecord::Migration[5.1]
+  class User < ApplicationRecord
+  end
+
+  def up
+    add_column :users, :plain_otp_secret, :string
+
+    key = twofa_encryption_key
+    decrypt_existing_secrets(key) if key
+
+    change_table :users, bulk: true do |t|
+      t.remove :encrypted_otp_secret
+      t.remove :encrypted_otp_secret_iv
+      t.remove :encrypted_otp_secret_salt
+    end
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
+
+  private
+
+  def twofa_encryption_key
+    if AppConfig.heroku?
+      ENV["TWOFA_ENCRYPTION_KEY"]
+    else
+      key_file = File.expand_path("../../config/initializers/twofa_encryption_key.rb", File.dirname(__FILE__))
+
+      if File.exist? key_file
+        require key_file
+        File.delete(key_file)
+
+        return Diaspora::Application.config.twofa_encryption_key
+      end
+    end
+  end
+
+  def decrypt_existing_secrets(key)
+    User.where.not(encrypted_otp_secret: nil).each do |user|
+      user.plain_otp_secret = Encryptor.decrypt(
+        value: user.encrypted_otp_secret.unpack("m").first,
+        key:   key,
+        iv:    user.encrypted_otp_secret_iv.unpack("m").first,
+        salt:  user.encrypted_otp_secret_salt.slice(1..-1).unpack("m").first
+      )
+      user.save!
+    end
+  end
+end

lib/configuration_methods.rb

@@ -68,24 +68,6 @@ module Configuration
       end
     end
 
-    def twofa_encryption_key
-      if heroku?
-        return ENV["TWOFA_ENCRYPTION_KEY"] if ENV["TWOFA_ENCRYPTION_KEY"]
-
-        warn "FATAL: Running on Heroku with TWOFA_ENCRYPTION_KEY unset"
-        warn "       Run heroku config:add TWOFA_ENCRYPTION_KEY=#{SecureRandom.hex(32)}"
-        abort
-      else
-        key_file = File.expand_path(
-          "../config/initializers/twofa_encryption_key.rb",
-          File.dirname(__FILE__)
-        )
-        system "DISABLE_SPRING=1 bin/rake generate:twofa_key" unless File.exist? key_file
-        require key_file
-        Diaspora::Application.config.twofa_encryption_key
-      end
-    end
-
     def version_string
       return @version_string unless @version_string.nil?
 

lib/tasks/generate_2fa_encription_key.rake

-# frozen_string_literal: true
-
-namespace :generate do
-  desc "Generates a key for encrypting 2fa tokens"
-  task :twofa_key do
-    path = Rails.root.join("config", "initializers", "twofa_encryption_key.rb")
-    key = SecureRandom.hex(32)
-    File.open(path, "w") do |f|
-      f.write <<~CONF
-        # frozen_string_literal: true
-
-        # The 2fa encryption key is used to encrypt users' OTP tokens in the database.
-
-        # You can regenerate this key by running `rake generate:twofa_key`
-
-        # If you change this key after a user has set up 2fa
-        # the users' tokens cannot be recovered
-        # and they will not be able to log in again!
-
-        Diaspora::Application.config.twofa_encryption_key = "#{key}"
-      CONF
-    end
-  end
-end

spec/models/user_spec.rb

@@ -984,9 +984,7 @@ describe User, :type => :model do
             exported_at
             exported_photos_at
             consumed_timestep
-            encrypted_otp_secret
-            encrypted_otp_secret_iv
-            encrypted_otp_secret_salt
+            plain_otp_secret
             otp_backup_codes
             otp_required_for_login
             otp_secret