diff --git a/shared/BoardConfig.mk b/shared/BoardConfig.mk
index 8df1ba9..07f5da1 100644
--- a/shared/BoardConfig.mk
+++ b/shared/BoardConfig.mk
@@ -162,6 +162,7 @@
   BOARD_SUPER_PARTITION_METADATA_DEVICE := vda
   BOARD_BUILD_SUPER_IMAGE_BY_DEFAULT := true
   BOARD_SUPER_IMAGE_IN_UPDATE_PACKAGE := true
+  TARGET_RELEASETOOLS_EXTENSIONS := device/google/cuttlefish/shared
 else
   # No dynamic partitions support; we must specify maximum sizes
   BOARD_SYSTEMIMAGE_PARTITION_SIZE := 4294967296 # 4 GB
diff --git a/shared/releasetools.py b/shared/releasetools.py
new file mode 100644
index 0000000..e401139
--- /dev/null
+++ b/shared/releasetools.py
@@ -0,0 +1,54 @@
+#
+# Copyright 2019 The Android Open-Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+import os
+
+from common import BlockDifference, EmptyImage, GetUserImage
+
+# The joint list of user image partitions of source and target builds.
+# - Items should be added to the list if new dynamic partitions are added.
+# - Items should not be removed from the list even if dynamic partitions are
+#   deleted. When generating an incremental OTA package, this script needs to
+#   know that an image is present in source build but not in target build.
+USERIMAGE_PARTITIONS = [
+    "product",
+]
+
+
+def GetUserImages(input_tmp, input_zip):
+  return {partition: GetUserImage(partition, input_tmp, input_zip)
+          for partition in USERIMAGE_PARTITIONS
+          if os.path.exists(os.path.join(input_tmp,
+                                         "IMAGES", partition + ".img"))}
+
+
+def FullOTA_GetBlockDifferences(info):
+  images = GetUserImages(info.input_tmp, info.input_zip)
+  return [BlockDifference(partition, image)
+          for partition, image in images.items()]
+
+
+def IncrementalOTA_GetBlockDifferences(info):
+  source_images = GetUserImages(info.source_tmp, info.source_zip)
+  target_images = GetUserImages(info.target_tmp, info.target_zip)
+
+  # Use EmptyImage() as a placeholder for partitions that will be deleted.
+  for partition in source_images:
+    target_images.setdefault(partition, EmptyImage())
+
+  # Use source_images.get() because new partitions are not in source_images.
+  return [BlockDifference(partition, target_image, source_images.get(partition))
+          for partition, target_image in target_images.items()]