diff --git a/activestorage/app/controllers/concerns/active_storage/set_blob.rb b/activestorage/app/controllers/concerns/active_storage/set_blob.rb
index f072954d7870c7ed6d43e5e6977e8ef763a6584a..e20d22be2be0e1dba47082850a70d707ee76300c 100644
--- a/activestorage/app/controllers/concerns/active_storage/set_blob.rb
+++ b/activestorage/app/controllers/concerns/active_storage/set_blob.rb
@@ -9,7 +9,7 @@ module ActiveStorage::SetBlob #:nodoc:
 
   private
     def set_blob
-      @blob = ActiveStorage::Blob.find_signed(params[:signed_blob_id] || params[:signed_id])
+      @blob = ActiveStorage::Blob.find_signed!(params[:signed_blob_id] || params[:signed_id])
     rescue ActiveSupport::MessageVerifier::InvalidSignature
       head :not_found
     end
diff --git a/activestorage/app/models/active_storage/blob.rb b/activestorage/app/models/active_storage/blob.rb
index b22e576b3ccecc73da6ca97353f491b0848098f5..163f633502c1d64a87803b301e3d644389770dff 100644
--- a/activestorage/app/models/active_storage/blob.rb
+++ b/activestorage/app/models/active_storage/blob.rb
@@ -35,6 +35,7 @@ class ActiveStorage::Blob < ActiveRecord::Base
   include ActiveStorage::Blob::Representable
 
   self.table_name = "active_storage_blobs"
+  self.signed_id_verifier = ActiveStorage.verifier
 
   MINIMUM_TOKEN_LENGTH = 28
 
@@ -72,8 +73,8 @@ class << self
     # that was created ahead of the upload itself on form submission.
     #
     # The signed ID is also used to create stable URLs for the blob through the BlobsController.
-    def find_signed(id, record: nil)
-      find ActiveStorage.verifier.verify(id, purpose: :blob_id)
+    def find_signed!(id, record: nil)
+      super(id, purpose: :blob_id)
     end
 
     def build_after_upload(io:, filename:, content_type: nil, metadata: nil, service_name: nil, identify: true, record: nil) #:nodoc:
@@ -125,12 +126,16 @@ def create_before_direct_upload!(key: nil, filename:, byte_size:, checksum:, con
     def generate_unique_secure_token(length: MINIMUM_TOKEN_LENGTH)
       SecureRandom.base36(length)
     end
+
+    # Customize signed ID purposes for backwards compatibility.
+    def combine_signed_id_purposes(purpose)
+      purpose.to_s
+    end
   end
 
   # Returns a signed ID for this blob that's suitable for reference on the client-side without fear of tampering.
-  # It uses the framework-wide verifier on <tt>ActiveStorage.verifier</tt>, but with a dedicated purpose.
   def signed_id
-    ActiveStorage.verifier.generate(id, purpose: :blob_id)
+    super(purpose: :blob_id)
   end
 
   # Returns the key pointing to the file on the service that's associated with this blob. The key is the
diff --git a/activestorage/lib/active_storage/attached/changes/create_one.rb b/activestorage/lib/active_storage/attached/changes/create_one.rb
index 498a6b5337349df66fb4746e4f5a2d913994bc15..b61d3b078c8c1d29dbfec693c864982ec82ae4d5 100644
--- a/activestorage/lib/active_storage/attached/changes/create_one.rb
+++ b/activestorage/lib/active_storage/attached/changes/create_one.rb
@@ -68,7 +68,7 @@ def find_or_build_blob
             )
           )
         when String
-          ActiveStorage::Blob.find_signed(attachable, record: record)
+          ActiveStorage::Blob.find_signed!(attachable, record: record)
         else
           raise ArgumentError, "Could not find or build blob: expected attachable, got #{attachable.inspect}"
         end
diff --git a/activestorage/test/controllers/direct_uploads_controller_test.rb b/activestorage/test/controllers/direct_uploads_controller_test.rb
index 17356c059048a9f876574e4cdd3043ed3260270c..734798ff3caa85af10b37cd07d7a919859376a01 100644
--- a/activestorage/test/controllers/direct_uploads_controller_test.rb
+++ b/activestorage/test/controllers/direct_uploads_controller_test.rb
@@ -21,7 +21,7 @@ class ActiveStorage::S3DirectUploadsControllerTest < ActionDispatch::Integration
         filename: "hello.txt", byte_size: 6, checksum: checksum, content_type: "text/plain" } }
 
       response.parsed_body.tap do |details|
-        assert_equal ActiveStorage::Blob.find(details["id"]), ActiveStorage::Blob.find_signed(details["signed_id"])
+        assert_equal ActiveStorage::Blob.find(details["id"]), ActiveStorage::Blob.find_signed!(details["signed_id"])
         assert_equal "hello.txt", details["filename"]
         assert_equal 6, details["byte_size"]
         assert_equal checksum, details["checksum"]
@@ -56,7 +56,7 @@ class ActiveStorage::GCSDirectUploadsControllerTest < ActionDispatch::Integratio
         filename: "hello.txt", byte_size: 6, checksum: checksum, content_type: "text/plain" } }
 
       @response.parsed_body.tap do |details|
-        assert_equal ActiveStorage::Blob.find(details["id"]), ActiveStorage::Blob.find_signed(details["signed_id"])
+        assert_equal ActiveStorage::Blob.find(details["id"]), ActiveStorage::Blob.find_signed!(details["signed_id"])
         assert_equal "hello.txt", details["filename"]
         assert_equal 6, details["byte_size"]
         assert_equal checksum, details["checksum"]
@@ -90,7 +90,7 @@ class ActiveStorage::AzureStorageDirectUploadsControllerTest < ActionDispatch::I
         filename: "hello.txt", byte_size: 6, checksum: checksum, content_type: "text/plain" } }
 
       @response.parsed_body.tap do |details|
-        assert_equal ActiveStorage::Blob.find(details["id"]), ActiveStorage::Blob.find_signed(details["signed_id"])
+        assert_equal ActiveStorage::Blob.find(details["id"]), ActiveStorage::Blob.find_signed!(details["signed_id"])
         assert_equal "hello.txt", details["filename"]
         assert_equal 6, details["byte_size"]
         assert_equal checksum, details["checksum"]
@@ -112,7 +112,7 @@ class ActiveStorage::DiskDirectUploadsControllerTest < ActionDispatch::Integrati
       filename: "hello.txt", byte_size: 6, checksum: checksum, content_type: "text/plain" } }
 
     @response.parsed_body.tap do |details|
-      assert_equal ActiveStorage::Blob.find(details["id"]), ActiveStorage::Blob.find_signed(details["signed_id"])
+      assert_equal ActiveStorage::Blob.find(details["id"]), ActiveStorage::Blob.find_signed!(details["signed_id"])
       assert_equal "hello.txt", details["filename"]
       assert_equal 6, details["byte_size"]
       assert_equal checksum, details["checksum"]
diff --git a/activestorage/test/models/attached/one_test.rb b/activestorage/test/models/attached/one_test.rb
index f3c5ead528a148477cc0159b87a37e15c0e5fb4c..304f32bf1525263cde568066369274855c522fcd 100644
--- a/activestorage/test/models/attached/one_test.rb
+++ b/activestorage/test/models/attached/one_test.rb
@@ -32,7 +32,7 @@ class ActiveStorage::OneAttachedTest < ActiveSupport::TestCase
   test "attaching an existing blob from a signed ID passes record" do
     blob = create_blob(filename: "funky.jpg")
     arguments = [blob.signed_id, record: @user]
-    assert_called_with(ActiveStorage::Blob, :find_signed, arguments, returns: blob) do
+    assert_called_with(ActiveStorage::Blob, :find_signed!, arguments, returns: blob) do
       @user.avatar.attach blob.signed_id
     end
   end
diff --git a/activestorage/test/models/attachment_test.rb b/activestorage/test/models/attachment_test.rb
index 88e83c32ab39c484037ab04b1f7280aeb4c85be7..ebcb837e86c6bbc8eec7a20aab9267f4287e5402 100644
--- a/activestorage/test/models/attachment_test.rb
+++ b/activestorage/test/models/attachment_test.rb
@@ -55,6 +55,14 @@ class ActiveStorage::AttachmentTest < ActiveSupport::TestCase
     @user.avatar.attach(blob)
 
     signed_id = @user.avatar.signed_id
-    assert_equal blob, ActiveStorage::Blob.find_signed(signed_id)
+    assert_equal blob, ActiveStorage::Blob.find_signed!(signed_id)
+  end
+
+  test "signed blob ID backwards compatibility" do
+    blob = create_blob
+    @user.avatar.attach(blob)
+
+    signed_id_generated_old_way = ActiveStorage.verifier.generate(@user.avatar.id, purpose: :blob_id)
+    assert_equal blob, ActiveStorage::Blob.find_signed!(signed_id_generated_old_way)
   end
 end