Change the default digest for new apps to SHA256

As mentioned in
https://github.com/rails/rails/pull/40770#issuecomment-748347066 we
should default to SHA256 where SHA1 is used today. This switches over
the ActiveSupport::Digest to use SHA256 for new applications.

It also updates the constants to always refer to and use the OpenSSL
constants as well, as also discussed in that PR.

activesupport/lib/active_support/digest.rb

@@ -1,10 +1,12 @@
 # frozen_string_literal: true
 
+require "openssl"
+
 module ActiveSupport
   class Digest #:nodoc:
     class <<self
       def hash_digest_class
-        @hash_digest_class ||= ::Digest::MD5
+        @hash_digest_class ||= OpenSSL::Digest::MD5
       end
 
       def hash_digest_class=(klass)

activesupport/lib/active_support/railtie.rb

@@ -88,9 +88,9 @@ module ActiveSupport
           ActiveSupport::Deprecation.warn(<<-MSG.squish)
             config.active_support.use_sha1_digests is deprecated and will
             be removed from Rails 6.2. Use
-            config.active_support.hash_digest_class = ::Digest::SHA1 instead.
+            config.active_support.hash_digest_class = OpenSSL::Digest::SHA1 instead.
           MSG
-          ActiveSupport::Digest.hash_digest_class = ::Digest::SHA1
+          ActiveSupport::Digest.hash_digest_class = OpenSSL::Digest::SHA1
         end
 
         if klass = app.config.active_support.hash_digest_class

activesupport/test/digest_test.rb

@@ -6,17 +6,17 @@ require "openssl"
 class DigestTest < ActiveSupport::TestCase
   class InvalidDigest; end
   def test_with_default_hash_digest_class
-    assert_equal ::Digest::MD5.hexdigest("hello friend"), ActiveSupport::Digest.hexdigest("hello friend")
+    assert_equal OpenSSL::Digest::MD5.hexdigest("hello friend"), ActiveSupport::Digest.hexdigest("hello friend")
   end
 
   def test_with_custom_hash_digest_class
     original_hash_digest_class = ActiveSupport::Digest.hash_digest_class
 
-    ActiveSupport::Digest.hash_digest_class = ::Digest::SHA1
+    ActiveSupport::Digest.hash_digest_class = OpenSSL::Digest::SHA1
     digest = ActiveSupport::Digest.hexdigest("hello friend")
 
     assert_equal 32, digest.length
-    assert_equal ::Digest::SHA1.hexdigest("hello friend")[0...32], digest
+    assert_equal OpenSSL::Digest::SHA1.hexdigest("hello friend")[0...32], digest
   ensure
     ActiveSupport::Digest.hash_digest_class = original_hash_digest_class
   end

guides/source/configuring.md

@@ -1041,6 +1041,7 @@ text/javascript image/svg+xml application/postscript application/x-shockwave-fla
 
 #### For '6.2', defaults from previous versions below and:
 - `config.active_support.key_generator_hash_digest_class`: `OpenSSL::Digest::SHA256`
+- `config.active_support.hash_digest_class`: `OpenSSL::Digest::SHA256`
 
 #### For '6.1', defaults from previous versions below and:
 
@@ -1076,7 +1077,7 @@ text/javascript image/svg+xml application/postscript application/x-shockwave-fla
 - `config.active_record.cache_versioning`: `true`
 - `config.action_dispatch.use_authenticated_cookie_encryption`: `true`
 - `config.active_support.use_authenticated_message_encryption`: `true`
-- `config.active_support.hash_digest_class`: `::Digest::SHA1`
+- `config.active_support.hash_digest_class`: `OpenSSL::Digest::SHA1`
 - `config.action_controller.default_protect_from_forgery`: `true`
 - `config.action_view.form_with_generates_ids`: `true`
 
@@ -1110,7 +1111,7 @@ text/javascript image/svg+xml application/postscript application/x-shockwave-fla
 - `config.active_record.has_many_inversing`: `false`
 - `config.active_record.legacy_connection_handling`: `true`
 - `config.active_support.use_authenticated_message_encryption`: `false`
-- `config.active_support.hash_digest_class`: `::Digest::MD5`
+- `config.active_support.hash_digest_class`: `OpenSSL::Digest::MD5`
 - `config.active_support.key_generator_hash_digest_class`: `OpenSSL::Digest::SHA1`
 - `ActiveSupport.utc_to_local_returns_utc_offset_times`: `false`
 

guides/source/upgrading_ruby_on_rails.md

@@ -101,6 +101,13 @@ Rails.application.config.action_dispatch.cookies_rotations.tap do |cookies|
 end
 ```
 
+### Digest class for ActiveSupport::Digest changing to SHA256
+
+The default digest class for ActiveSupport::Digest is changing from SHA1 to SHA256.
+This has consequences for things like Etags that will change and cache keys as well.
+Changing these keys can have impact on cache hit rates, so be careful and watch out
+for this when upgrading to the new hash.
+
 Upgrading from Rails 6.0 to Rails 6.1
 -------------------------------------
 

railties/lib/rails/application/configuration.rb

@@ -116,7 +116,7 @@ module Rails
 
           if respond_to?(:active_support)
             active_support.use_authenticated_message_encryption = true
-            active_support.hash_digest_class = ::Digest::SHA1
+            active_support.hash_digest_class = OpenSSL::Digest::SHA1
           end
 
           if respond_to?(:action_controller)
@@ -209,6 +209,7 @@ module Rails
           end
 
           if respond_to?(:active_support)
+            active_support.hash_digest_class = OpenSSL::Digest::SHA256
             active_support.key_generator_hash_digest_class = OpenSSL::Digest::SHA256
           end
         else

railties/lib/rails/generators/rails/app/templates/config/initializers/new_framework_defaults_6_2.rb.tt

@@ -9,11 +9,17 @@
 # button_to view helpers consistently render <button> elements.
 # Rails.application.config.action_view.button_to_generates_button_tag = false
 
-# Change the digest class for they key generators to `OpenSSL::Digest::SHA256`.
+# Change the digest class for the key generators to `OpenSSL::Digest::SHA256`.
-# Changing this defaults means invalidate all encripted messages generated by
+# Changing this default means invalidate all encrypted messages generated by
 # your application and, all the encrypted cookies. Only change this after you
-# rotated all the messages using they key rotator.
+# rotated all the messages using the key rotator.
 #
 # See upgrading guide for more information on how to build a rotator.
 # https://guides.rubyonrails.org/v7.0/upgrading_ruby_on_rails.html
 # Rails.application.config.active_support.key_generator_hash_digest_class = OpenSSL::Digest::SHA256
+
+# Change the digest class for ActiveSupport::Digest.
+# Changing this default means that for example Etags change and
+# various cache keys leading to cache invalidation.
+#
+# Rails.application.config.active_support.hash_digest_class = OpenSSL::Digest::SHA256

railties/test/application/configuration_test.rb

@@ -2257,18 +2257,18 @@ module ApplicationTests
       assert_equal true, ActiveSupport::MessageEncryptor.use_authenticated_message_encryption
     end
 
-    test "ActiveSupport::Digest.hash_digest_class is Digest::SHA1 by default for new apps" do
+    test "ActiveSupport::Digest.hash_digest_class is OpenSSL::Digest::SHA256 by default for new apps" do
       app "development"
 
-      assert_equal Digest::SHA1, ActiveSupport::Digest.hash_digest_class
+      assert_equal OpenSSL::Digest::SHA256, ActiveSupport::Digest.hash_digest_class
     end
 
-    test "ActiveSupport::Digest.hash_digest_class is Digest::MD5 by default for upgraded apps" do
+    test "ActiveSupport::Digest.hash_digest_class is OpenSSL::Digest::MD5 by default for upgraded apps" do
       remove_from_config '.*config\.load_defaults.*\n'
 
       app "development"
 
-      assert_equal Digest::MD5, ActiveSupport::Digest.hash_digest_class
+      assert_equal OpenSSL::Digest::MD5, ActiveSupport::Digest.hash_digest_class
     end
 
     test "ActiveSupport::Digest.hash_digest_class can be configured via config.active_support.use_sha1_digests" do
@@ -2280,19 +2280,19 @@ module ApplicationTests
 
       app "development"
 
-      assert_equal Digest::SHA1, ActiveSupport::Digest.hash_digest_class
+      assert_equal OpenSSL::Digest::SHA1, ActiveSupport::Digest.hash_digest_class
     end
 
     test "ActiveSupport::Digest.hash_digest_class can be configured via config.active_support.hash_digest_class" do
       remove_from_config '.*config\.load_defaults.*\n'
 
       app_file "config/initializers/custom_digest_class.rb", <<-RUBY
-        Rails.application.config.active_support.hash_digest_class = Digest::SHA256
+        Rails.application.config.active_support.hash_digest_class = OpenSSL::Digest::SHA256
       RUBY
 
       app "development"
 
-      assert_equal Digest::SHA256, ActiveSupport::Digest.hash_digest_class
+      assert_equal OpenSSL::Digest::SHA256, ActiveSupport::Digest.hash_digest_class
     end
 
     test "ActiveSupport::KeyGenerator.hash_digest_class is OpenSSL::Digest::SHA256 by default for new apps" do

railties/test/application/per_request_digest_cache_test.rb

@@ -57,7 +57,7 @@ class PerRequestDigestCacheTest < ActiveSupport::TestCase
     assert_equal 200, last_response.status
 
     values = ActionView::LookupContext::DetailsKey.digest_caches.first.values
-    assert_equal [ "effc8928d0b33535c8a21d24ec617161" ], values
+    assert_equal [ "ddb451d2c1b2374caa676005893bb776" ], values
     assert_equal %w(david dingus), last_response.body.split.map(&:strip)
   end