Add handling of Linked Data Signatures in payloads (#4687)

* Add handling of Linked Data Signatures in payloads

* Add a way to sign JSON, fix canonicalization of signature options

* Fix signatureValue encoding, send out signed JSON when distributing

* Add missing security context

app/helpers/jsonld_helper.rb

@@ -17,6 +17,11 @@ module JsonLdHelper
     !json.nil? && equals_or_includes?(json['@context'], ActivityPub::TagManager::CONTEXT)
   end
 
+  def canonicalize(json)
+    graph = RDF::Graph.new << JSON::LD::API.toRdf(json)
+    graph.dump(:normalize)
+  end
+
   def fetch_resource(uri)
     response = build_request(uri).perform
     return if response.code != 200
@@ -29,6 +34,14 @@ module JsonLdHelper
     nil
   end
 
+  def merge_context(context, new_context)
+    if context.is_a?(Array)
+      context << new_context
+    else
+      [context, new_context]
+    end
+  end
+
   private
 
   def build_request(uri)

app/lib/activitypub/adapter.rb

@@ -11,7 +11,7 @@ class ActivityPub::Adapter < ActiveModelSerializers::Adapter::Base
 
   def serializable_hash(options = nil)
     options = serialization_options(options)
-    serialized_hash = { '@context': ActivityPub::TagManager::CONTEXT }.merge(ActiveModelSerializers::Adapter::Attributes.new(serializer, instance_options).serializable_hash(options))
+    serialized_hash = { '@context': [ActivityPub::TagManager::CONTEXT, 'https://w3id.org/security/v1'] }.merge(ActiveModelSerializers::Adapter::Attributes.new(serializer, instance_options).serializable_hash(options))
     self.class.transform_key_casing!(serialized_hash, instance_options)
   end
 end

app/lib/activitypub/linked_data_signature.rb

@@ -0,0 +1,56 @@
+# frozen_string_literal: true
+
+class ActivityPub::LinkedDataSignature
+  include JsonLdHelper
+
+  CONTEXT = 'https://w3id.org/identity/v1'
+
+  def initialize(json)
+    @json = json
+  end
+
+  def verify_account!
+    return unless @json['signature'].is_a?(Hash)
+
+    type        = @json['signature']['type']
+    creator_uri = @json['signature']['creator']
+    signature   = @json['signature']['signatureValue']
+
+    return unless type == 'RsaSignature2017'
+
+    creator   = ActivityPub::TagManager.instance.uri_to_resource(creator_uri, Account)
+    creator ||= ActivityPub::FetchRemoteKeyService.new.call(creator_uri)
+
+    return if creator.nil?
+
+    options_hash   = hash(@json['signature'].without('type', 'id', 'signatureValue').merge('@context' => CONTEXT))
+    document_hash  = hash(@json.without('signature'))
+    to_be_verified = options_hash + document_hash
+
+    if creator.keypair.public_key.verify(OpenSSL::Digest::SHA256.new, Base64.decode64(signature), to_be_verified)
+      creator
+    end
+  end
+
+  def sign!(creator)
+    options = {
+      'type'    => 'RsaSignature2017',
+      'creator' => [ActivityPub::TagManager.instance.uri_for(creator), '#main-key'].join,
+      'created' => Time.now.utc.iso8601,
+    }
+
+    options_hash  = hash(options.without('type', 'id', 'signatureValue').merge('@context' => CONTEXT))
+    document_hash = hash(@json.without('signature'))
+    to_be_signed  = options_hash + document_hash
+
+    signature = Base64.strict_encode64(creator.keypair.sign(OpenSSL::Digest::SHA256.new, to_be_signed))
+
+    @json.merge('@context' => merge_context(@json['@context'], CONTEXT), 'signature' => options.merge('signatureValue' => signature))
+  end
+
+  private
+
+  def hash(obj)
+    Digest::SHA256.hexdigest(canonicalize(obj))
+  end
+end

app/services/activitypub/process_collection_service.rb

@@ -9,6 +9,8 @@ class ActivityPub::ProcessCollectionService < BaseService
 
     return if @account.suspended? || !supported_context?
 
+    verify_account! if different_actor?
+
     case @json['type']
     when 'Collection', 'CollectionPage'
       process_items @json['items']
@@ -23,6 +25,10 @@ class ActivityPub::ProcessCollectionService < BaseService
 
   private
 
+  def different_actor?
+    @json['actor'].present? && value_or_id(@json['actor']) != @account.uri && @json['signature'].present?
+  end
+
   def process_items(items)
     items.reverse_each.map { |item| process_item(item) }.compact
   end
@@ -35,4 +41,9 @@ class ActivityPub::ProcessCollectionService < BaseService
     activity = ActivityPub::Activity.factory(item, @account)
     activity&.perform
   end
+
+  def verify_account!
+    account  = ActivityPub::LinkedDataSignature.new(@json).verify_account!
+    @account = account unless account.nil?
+  end
 end

app/services/authorize_follow_service.rb

@@ -24,11 +24,11 @@ class AuthorizeFollowService < BaseService
   end
 
   def build_json(follow_request)
-    ActiveModelSerializers::SerializableResource.new(
+    Oj.dump(ActivityPub::LinkedDataSignature.new(ActiveModelSerializers::SerializableResource.new(
       follow_request,
       serializer: ActivityPub::AcceptFollowSerializer,
       adapter: ActivityPub::Adapter
-    ).to_json
+    ).as_json).sign!(follow_request.target_account))
   end
 
   def build_xml(follow_request)

app/services/batched_remove_status_service.rb

@@ -138,10 +138,14 @@ class BatchedRemoveStatusService < BaseService
   def build_json(status)
     return @activity_json[status.id] if @activity_json.key?(status.id)
 
-    @activity_json[status.id] = ActiveModelSerializers::SerializableResource.new(
+    @activity_json[status.id] = sign_json(status, ActiveModelSerializers::SerializableResource.new(
       status,
       serializer: ActivityPub::DeleteSerializer,
       adapter: ActivityPub::Adapter
-    ).to_json
+    ).as_json)
+  end
+
+  def sign_json(status, json)
+    Oj.dump(ActivityPub::LinkedDataSignature.new(json).sign!(status.account))
   end
 end

app/services/block_service.rb

@@ -27,11 +27,11 @@ class BlockService < BaseService
   end
 
   def build_json(block)
-    ActiveModelSerializers::SerializableResource.new(
+    Oj.dump(ActivityPub::LinkedDataSignature.new(ActiveModelSerializers::SerializableResource.new(
       block,
       serializer: ActivityPub::BlockSerializer,
       adapter: ActivityPub::Adapter
-    ).to_json
+    ).as_json).sign!(block.account))
   end
 
   def build_xml(block)

app/services/favourite_service.rb

@@ -34,11 +34,11 @@ class FavouriteService < BaseService
   end
 
   def build_json(favourite)
-    ActiveModelSerializers::SerializableResource.new(
+    Oj.dump(ActivityPub::LinkedDataSignature.new(ActiveModelSerializers::SerializableResource.new(
       favourite,
       serializer: ActivityPub::LikeSerializer,
       adapter: ActivityPub::Adapter
-    ).to_json
+    ).as_json).sign!(favourite.account))
   end
 
   def build_xml(favourite)

app/services/follow_service.rb

@@ -67,10 +67,10 @@ class FollowService < BaseService
   end
 
   def build_json(follow_request)
-    ActiveModelSerializers::SerializableResource.new(
+    Oj.dump(ActivityPub::LinkedDataSignature.new(ActiveModelSerializers::SerializableResource.new(
       follow_request,
       serializer: ActivityPub::FollowSerializer,
       adapter: ActivityPub::Adapter
-    ).to_json
+    ).as_json).sign!(follow_request.account))
   end
 end

app/services/process_mentions_service.rb

@@ -47,11 +47,11 @@ class ProcessMentionsService < BaseService
   end
 
   def build_json(status)
-    ActiveModelSerializers::SerializableResource.new(
+    Oj.dump(ActivityPub::LinkedDataSignature.new(ActiveModelSerializers::SerializableResource.new(
       status,
       serializer: ActivityPub::ActivitySerializer,
       adapter: ActivityPub::Adapter
-    ).to_json
+    ).as_json).sign!(status.account))
   end
 
   def follow_remote_account_service

app/services/reblog_service.rb

@@ -42,10 +42,10 @@ class ReblogService < BaseService
   end
 
   def build_json(reblog)
-    ActiveModelSerializers::SerializableResource.new(
+    Oj.dump(ActivityPub::LinkedDataSignature.new(ActiveModelSerializers::SerializableResource.new(
       reblog,
       serializer: ActivityPub::ActivitySerializer,
       adapter: ActivityPub::Adapter
-    ).to_json
+    ).as_json).sign!(reblog.account))
   end
 end

app/services/reject_follow_service.rb

@@ -19,11 +19,11 @@ class RejectFollowService < BaseService
   end
 
   def build_json(follow_request)
-    ActiveModelSerializers::SerializableResource.new(
+    Oj.dump(ActivityPub::LinkedDataSignature.new(ActiveModelSerializers::SerializableResource.new(
       follow_request,
       serializer: ActivityPub::RejectFollowSerializer,
       adapter: ActivityPub::Adapter
-    ).to_json
+    ).as_json).sign!(follow_request.target_account))
   end
 
   def build_xml(follow_request)

app/services/remove_status_service.rb

@@ -56,7 +56,7 @@ class RemoveStatusService < BaseService
 
     # ActivityPub
     ActivityPub::DeliveryWorker.push_bulk(target_accounts.select(&:activitypub?).uniq(&:inbox_url)) do |inbox_url|
-      [activity_json, @account.id, inbox_url]
+      [signed_activity_json, @account.id, inbox_url]
     end
   end
 
@@ -66,7 +66,7 @@ class RemoveStatusService < BaseService
 
     # ActivityPub
     ActivityPub::DeliveryWorker.push_bulk(@account.followers.inboxes) do |inbox_url|
-      [activity_json, @account.id, inbox_url]
+      [signed_activity_json, @account.id, inbox_url]
     end
   end
 
@@ -74,12 +74,16 @@ class RemoveStatusService < BaseService
     @salmon_xml ||= stream_entry_to_xml(@stream_entry)
   end
 
+  def signed_activity_json
+    @signed_activity_json ||= Oj.dump(ActivityPub::LinkedDataSignature.new(activity_json).sign!(@account))
+  end
+
   def activity_json
     @activity_json ||= ActiveModelSerializers::SerializableResource.new(
       @status,
       serializer: ActivityPub::DeleteSerializer,
       adapter: ActivityPub::Adapter
-    ).to_json
+    ).as_json
   end
 
   def remove_reblogs

app/services/unblock_service.rb

@@ -20,11 +20,11 @@ class UnblockService < BaseService
   end
 
   def build_json(unblock)
-    ActiveModelSerializers::SerializableResource.new(
+    Oj.dump(ActivityPub::LinkedDataSignature.new(ActiveModelSerializers::SerializableResource.new(
       unblock,
       serializer: ActivityPub::UndoBlockSerializer,
       adapter: ActivityPub::Adapter
-    ).to_json
+    ).as_json).sign!(unblock.account))
   end
 
   def build_xml(block)

app/services/unfavourite_service.rb

@@ -21,11 +21,11 @@ class UnfavouriteService < BaseService
   end
 
   def build_json(favourite)
-    ActiveModelSerializers::SerializableResource.new(
+    Oj.dump(ActivityPub::LinkedDataSignature.new(ActiveModelSerializers::SerializableResource.new(
       favourite,
       serializer: ActivityPub::UndoLikeSerializer,
       adapter: ActivityPub::Adapter
-    ).to_json
+    ).as_json).sign!(favourite.account))
   end
 
   def build_xml(favourite)

app/services/unfollow_service.rb

@@ -23,11 +23,11 @@ class UnfollowService < BaseService
   end
 
   def build_json(follow)
-    ActiveModelSerializers::SerializableResource.new(
+    Oj.dump(ActivityPub::LinkedDataSignature.new(ActiveModelSerializers::SerializableResource.new(
       follow,
       serializer: ActivityPub::UndoFollowSerializer,
       adapter: ActivityPub::Adapter
-    ).to_json
+    ).as_json).sign!(follow.account))
   end
 
   def build_xml(follow)

app/workers/activitypub/distribution_worker.rb

@@ -12,7 +12,7 @@ class ActivityPub::DistributionWorker
     return if skip_distribution?
 
     ActivityPub::DeliveryWorker.push_bulk(inboxes) do |inbox_url|
-      [payload, @account.id, inbox_url]
+      [signed_payload, @account.id, inbox_url]
     end
   rescue ActiveRecord::RecordNotFound
     true
@@ -28,11 +28,15 @@ class ActivityPub::DistributionWorker
     @inboxes ||= @account.followers.inboxes
   end
 
+  def signed_payload
+    @signed_payload ||= Oj.dump(ActivityPub::LinkedDataSignature.new(payload).sign!(@account))
+  end
+
   def payload
     @payload ||= ActiveModelSerializers::SerializableResource.new(
       @status,
       serializer: ActivityPub::ActivitySerializer,
       adapter: ActivityPub::Adapter
-    ).to_json
+    ).as_json
   end
 end