diff --git a/tools/releasetools/ota_from_target_files.py b/tools/releasetools/ota_from_target_files.py
index 65644e1..7aada51 100755
--- a/tools/releasetools/ota_from_target_files.py
+++ b/tools/releasetools/ota_from_target_files.py
@@ -255,7 +255,6 @@
 import re
 import shlex
 import shutil
-import struct
 import subprocess
 import sys
 import zipfile
@@ -264,7 +263,7 @@
 import common
 import ota_utils
 from ota_utils import (UNZIP_PATTERN, FinalizeMetadata, GetPackageMetadata,
-                       PropertyFiles, SECURITY_PATCH_LEVEL_PROP_NAME, GetZipEntryOffset)
+                       Payload, SECURITY_PATCH_LEVEL_PROP_NAME, StreamingPropertyFiles, AbOtaPropertyFiles)
 from common import IsSparseImage
 import target_files_diff
 from check_target_files_vintf import CheckVintfIfTrebleEnabled
@@ -336,143 +335,6 @@
     'vendor', 'vendor_boot']
 
 
-class Payload(object):
-  """Manages the creation and the signing of an A/B OTA Payload."""
-
-  PAYLOAD_BIN = 'payload.bin'
-  PAYLOAD_PROPERTIES_TXT = 'payload_properties.txt'
-  SECONDARY_PAYLOAD_BIN = 'secondary/payload.bin'
-  SECONDARY_PAYLOAD_PROPERTIES_TXT = 'secondary/payload_properties.txt'
-
-  def __init__(self, secondary=False):
-    """Initializes a Payload instance.
-
-    Args:
-      secondary: Whether it's generating a secondary payload (default: False).
-    """
-    self.payload_file = None
-    self.payload_properties = None
-    self.secondary = secondary
-
-  def _Run(self, cmd):  # pylint: disable=no-self-use
-    # Don't pipe (buffer) the output if verbose is set. Let
-    # brillo_update_payload write to stdout/stderr directly, so its progress can
-    # be monitored.
-    if OPTIONS.verbose:
-      common.RunAndCheckOutput(cmd, stdout=None, stderr=None)
-    else:
-      common.RunAndCheckOutput(cmd)
-
-  def Generate(self, target_file, source_file=None, additional_args=None):
-    """Generates a payload from the given target-files zip(s).
-
-    Args:
-      target_file: The filename of the target build target-files zip.
-      source_file: The filename of the source build target-files zip; or None if
-          generating a full OTA.
-      additional_args: A list of additional args that should be passed to
-          brillo_update_payload script; or None.
-    """
-    if additional_args is None:
-      additional_args = []
-
-    payload_file = common.MakeTempFile(prefix="payload-", suffix=".bin")
-    cmd = ["brillo_update_payload", "generate",
-           "--payload", payload_file,
-           "--target_image", target_file]
-    if source_file is not None:
-      cmd.extend(["--source_image", source_file])
-      if OPTIONS.disable_fec_computation:
-        cmd.extend(["--disable_fec_computation", "true"])
-      if OPTIONS.disable_verity_computation:
-        cmd.extend(["--disable_verity_computation", "true"])
-    cmd.extend(additional_args)
-    self._Run(cmd)
-
-    self.payload_file = payload_file
-    self.payload_properties = None
-
-  def Sign(self, payload_signer):
-    """Generates and signs the hashes of the payload and metadata.
-
-    Args:
-      payload_signer: A PayloadSigner() instance that serves the signing work.
-
-    Raises:
-      AssertionError: On any failure when calling brillo_update_payload script.
-    """
-    assert isinstance(payload_signer, PayloadSigner)
-
-    # 1. Generate hashes of the payload and metadata files.
-    payload_sig_file = common.MakeTempFile(prefix="sig-", suffix=".bin")
-    metadata_sig_file = common.MakeTempFile(prefix="sig-", suffix=".bin")
-    cmd = ["brillo_update_payload", "hash",
-           "--unsigned_payload", self.payload_file,
-           "--signature_size", str(payload_signer.maximum_signature_size),
-           "--metadata_hash_file", metadata_sig_file,
-           "--payload_hash_file", payload_sig_file]
-    self._Run(cmd)
-
-    # 2. Sign the hashes.
-    signed_payload_sig_file = payload_signer.Sign(payload_sig_file)
-    signed_metadata_sig_file = payload_signer.Sign(metadata_sig_file)
-
-    # 3. Insert the signatures back into the payload file.
-    signed_payload_file = common.MakeTempFile(prefix="signed-payload-",
-                                              suffix=".bin")
-    cmd = ["brillo_update_payload", "sign",
-           "--unsigned_payload", self.payload_file,
-           "--payload", signed_payload_file,
-           "--signature_size", str(payload_signer.maximum_signature_size),
-           "--metadata_signature_file", signed_metadata_sig_file,
-           "--payload_signature_file", signed_payload_sig_file]
-    self._Run(cmd)
-
-    # 4. Dump the signed payload properties.
-    properties_file = common.MakeTempFile(prefix="payload-properties-",
-                                          suffix=".txt")
-    cmd = ["brillo_update_payload", "properties",
-           "--payload", signed_payload_file,
-           "--properties_file", properties_file]
-    self._Run(cmd)
-
-    if self.secondary:
-      with open(properties_file, "a") as f:
-        f.write("SWITCH_SLOT_ON_REBOOT=0\n")
-
-    if OPTIONS.wipe_user_data:
-      with open(properties_file, "a") as f:
-        f.write("POWERWASH=1\n")
-
-    self.payload_file = signed_payload_file
-    self.payload_properties = properties_file
-
-  def WriteToZip(self, output_zip):
-    """Writes the payload to the given zip.
-
-    Args:
-      output_zip: The output ZipFile instance.
-    """
-    assert self.payload_file is not None
-    assert self.payload_properties is not None
-
-    if self.secondary:
-      payload_arcname = Payload.SECONDARY_PAYLOAD_BIN
-      payload_properties_arcname = Payload.SECONDARY_PAYLOAD_PROPERTIES_TXT
-    else:
-      payload_arcname = Payload.PAYLOAD_BIN
-      payload_properties_arcname = Payload.PAYLOAD_PROPERTIES_TXT
-
-    # Add the signed payload file and properties into the zip. In order to
-    # support streaming, we pack them as ZIP_STORED. So these entries can be
-    # read directly with the offset and length pairs.
-    common.ZipWrite(output_zip, self.payload_file, arcname=payload_arcname,
-                    compress_type=zipfile.ZIP_STORED)
-    common.ZipWrite(output_zip, self.payload_properties,
-                    arcname=payload_properties_arcname,
-                    compress_type=zipfile.ZIP_STORED)
-
-
 def _LoadOemDicts(oem_source):
   """Returns the list of loaded OEM properties dict."""
   if not oem_source:
@@ -484,113 +346,6 @@
   return oem_dicts
 
 
-class StreamingPropertyFiles(PropertyFiles):
-  """A subclass for computing the property-files for streaming A/B OTAs."""
-
-  def __init__(self):
-    super(StreamingPropertyFiles, self).__init__()
-    self.name = 'ota-streaming-property-files'
-    self.required = (
-        # payload.bin and payload_properties.txt must exist.
-        'payload.bin',
-        'payload_properties.txt',
-    )
-    self.optional = (
-        # apex_info.pb isn't directly used in the update flow
-        'apex_info.pb',
-        # care_map is available only if dm-verity is enabled.
-        'care_map.pb',
-        'care_map.txt',
-        # compatibility.zip is available only if target supports Treble.
-        'compatibility.zip',
-    )
-
-
-class AbOtaPropertyFiles(StreamingPropertyFiles):
-  """The property-files for A/B OTA that includes payload_metadata.bin info.
-
-  Since P, we expose one more token (aka property-file), in addition to the ones
-  for streaming A/B OTA, for a virtual entry of 'payload_metadata.bin'.
-  'payload_metadata.bin' is the header part of a payload ('payload.bin'), which
-  doesn't exist as a separate ZIP entry, but can be used to verify if the
-  payload can be applied on the given device.
-
-  For backward compatibility, we keep both of the 'ota-streaming-property-files'
-  and the newly added 'ota-property-files' in P. The new token will only be
-  available in 'ota-property-files'.
-  """
-
-  def __init__(self):
-    super(AbOtaPropertyFiles, self).__init__()
-    self.name = 'ota-property-files'
-
-  def _GetPrecomputed(self, input_zip):
-    offset, size = self._GetPayloadMetadataOffsetAndSize(input_zip)
-    return ['payload_metadata.bin:{}:{}'.format(offset, size)]
-
-  @staticmethod
-  def _GetPayloadMetadataOffsetAndSize(input_zip):
-    """Computes the offset and size of the payload metadata for a given package.
-
-    (From system/update_engine/update_metadata.proto)
-    A delta update file contains all the deltas needed to update a system from
-    one specific version to another specific version. The update format is
-    represented by this struct pseudocode:
-
-    struct delta_update_file {
-      char magic[4] = "CrAU";
-      uint64 file_format_version;
-      uint64 manifest_size;  // Size of protobuf DeltaArchiveManifest
-
-      // Only present if format_version > 1:
-      uint32 metadata_signature_size;
-
-      // The Bzip2 compressed DeltaArchiveManifest
-      char manifest[metadata_signature_size];
-
-      // The signature of the metadata (from the beginning of the payload up to
-      // this location, not including the signature itself). This is a
-      // serialized Signatures message.
-      char medatada_signature_message[metadata_signature_size];
-
-      // Data blobs for files, no specific format. The specific offset
-      // and length of each data blob is recorded in the DeltaArchiveManifest.
-      struct {
-        char data[];
-      } blobs[];
-
-      // These two are not signed:
-      uint64 payload_signatures_message_size;
-      char payload_signatures_message[];
-    };
-
-    'payload-metadata.bin' contains all the bytes from the beginning of the
-    payload, till the end of 'medatada_signature_message'.
-    """
-    payload_info = input_zip.getinfo('payload.bin')
-    (payload_offset, payload_size) = GetZipEntryOffset(input_zip, payload_info)
-
-    # Read the underlying raw zipfile at specified offset
-    payload_fp = input_zip.fp
-    payload_fp.seek(payload_offset)
-    header_bin = payload_fp.read(24)
-
-    # network byte order (big-endian)
-    header = struct.unpack("!IQQL", header_bin)
-
-    # 'CrAU'
-    magic = header[0]
-    assert magic == 0x43724155, "Invalid magic: {:x}, computed offset {}" \
-        .format(magic, payload_offset)
-
-    manifest_size = header[2]
-    metadata_signature_size = header[3]
-    metadata_total = 24 + manifest_size + metadata_signature_size
-    assert metadata_total < payload_size
-
-    return (payload_offset, metadata_total)
-
-
 def ModifyVABCCompressionParam(content, algo):
   """ Update update VABC Compression Param in dynamic_partitions_info.txt
   Args:
diff --git a/tools/releasetools/ota_utils.py b/tools/releasetools/ota_utils.py
index 12acc13..e593eb3 100644
--- a/tools/releasetools/ota_utils.py
+++ b/tools/releasetools/ota_utils.py
@@ -21,10 +21,13 @@
 import zipfile
 
 import ota_metadata_pb2
+import common
 from common import (ZipDelete, ZipClose, OPTIONS, MakeTempFile,
                     ZipWriteStr, BuildInfo, LoadDictionaryFromFile,
                     SignFile, PARTITIONS_WITH_BUILD_PROP, PartitionBuildProps,
                     GetRamdiskFormat)
+from payload_signer import PayloadSigner
+
 
 logger = logging.getLogger(__name__)
 
@@ -702,3 +705,247 @@
   sourceEntry = ReadEntry(source_file, _ZUCCHINI_CONFIG_ENTRY_NAME)
   targetEntry = ReadEntry(target_file, _ZUCCHINI_CONFIG_ENTRY_NAME)
   return sourceEntry and targetEntry and sourceEntry == targetEntry
+
+
+class Payload(object):
+  """Manages the creation and the signing of an A/B OTA Payload."""
+
+  PAYLOAD_BIN = 'payload.bin'
+  PAYLOAD_PROPERTIES_TXT = 'payload_properties.txt'
+  SECONDARY_PAYLOAD_BIN = 'secondary/payload.bin'
+  SECONDARY_PAYLOAD_PROPERTIES_TXT = 'secondary/payload_properties.txt'
+
+  def __init__(self, secondary=False):
+    """Initializes a Payload instance.
+
+    Args:
+      secondary: Whether it's generating a secondary payload (default: False).
+    """
+    self.payload_file = None
+    self.payload_properties = None
+    self.secondary = secondary
+
+  def _Run(self, cmd):  # pylint: disable=no-self-use
+    # Don't pipe (buffer) the output if verbose is set. Let
+    # brillo_update_payload write to stdout/stderr directly, so its progress can
+    # be monitored.
+    if OPTIONS.verbose:
+      common.RunAndCheckOutput(cmd, stdout=None, stderr=None)
+    else:
+      common.RunAndCheckOutput(cmd)
+
+  def Generate(self, target_file, source_file=None, additional_args=None):
+    """Generates a payload from the given target-files zip(s).
+
+    Args:
+      target_file: The filename of the target build target-files zip.
+      source_file: The filename of the source build target-files zip; or None if
+          generating a full OTA.
+      additional_args: A list of additional args that should be passed to
+          brillo_update_payload script; or None.
+    """
+    if additional_args is None:
+      additional_args = []
+
+    payload_file = common.MakeTempFile(prefix="payload-", suffix=".bin")
+    cmd = ["brillo_update_payload", "generate",
+           "--payload", payload_file,
+           "--target_image", target_file]
+    if source_file is not None:
+      cmd.extend(["--source_image", source_file])
+      if OPTIONS.disable_fec_computation:
+        cmd.extend(["--disable_fec_computation", "true"])
+      if OPTIONS.disable_verity_computation:
+        cmd.extend(["--disable_verity_computation", "true"])
+    cmd.extend(additional_args)
+    self._Run(cmd)
+
+    self.payload_file = payload_file
+    self.payload_properties = None
+
+  def Sign(self, payload_signer):
+    """Generates and signs the hashes of the payload and metadata.
+
+    Args:
+      payload_signer: A PayloadSigner() instance that serves the signing work.
+
+    Raises:
+      AssertionError: On any failure when calling brillo_update_payload script.
+    """
+    assert isinstance(payload_signer, PayloadSigner)
+
+    # 1. Generate hashes of the payload and metadata files.
+    payload_sig_file = common.MakeTempFile(prefix="sig-", suffix=".bin")
+    metadata_sig_file = common.MakeTempFile(prefix="sig-", suffix=".bin")
+    cmd = ["brillo_update_payload", "hash",
+           "--unsigned_payload", self.payload_file,
+           "--signature_size", str(payload_signer.maximum_signature_size),
+           "--metadata_hash_file", metadata_sig_file,
+           "--payload_hash_file", payload_sig_file]
+    self._Run(cmd)
+
+    # 2. Sign the hashes.
+    signed_payload_sig_file = payload_signer.Sign(payload_sig_file)
+    signed_metadata_sig_file = payload_signer.Sign(metadata_sig_file)
+
+    # 3. Insert the signatures back into the payload file.
+    signed_payload_file = common.MakeTempFile(prefix="signed-payload-",
+                                              suffix=".bin")
+    cmd = ["brillo_update_payload", "sign",
+           "--unsigned_payload", self.payload_file,
+           "--payload", signed_payload_file,
+           "--signature_size", str(payload_signer.maximum_signature_size),
+           "--metadata_signature_file", signed_metadata_sig_file,
+           "--payload_signature_file", signed_payload_sig_file]
+    self._Run(cmd)
+
+    # 4. Dump the signed payload properties.
+    properties_file = common.MakeTempFile(prefix="payload-properties-",
+                                          suffix=".txt")
+    cmd = ["brillo_update_payload", "properties",
+           "--payload", signed_payload_file,
+           "--properties_file", properties_file]
+    self._Run(cmd)
+
+    if self.secondary:
+      with open(properties_file, "a") as f:
+        f.write("SWITCH_SLOT_ON_REBOOT=0\n")
+
+    if OPTIONS.wipe_user_data:
+      with open(properties_file, "a") as f:
+        f.write("POWERWASH=1\n")
+
+    self.payload_file = signed_payload_file
+    self.payload_properties = properties_file
+
+  def WriteToZip(self, output_zip):
+    """Writes the payload to the given zip.
+
+    Args:
+      output_zip: The output ZipFile instance.
+    """
+    assert self.payload_file is not None
+    assert self.payload_properties is not None
+
+    if self.secondary:
+      payload_arcname = Payload.SECONDARY_PAYLOAD_BIN
+      payload_properties_arcname = Payload.SECONDARY_PAYLOAD_PROPERTIES_TXT
+    else:
+      payload_arcname = Payload.PAYLOAD_BIN
+      payload_properties_arcname = Payload.PAYLOAD_PROPERTIES_TXT
+
+    # Add the signed payload file and properties into the zip. In order to
+    # support streaming, we pack them as ZIP_STORED. So these entries can be
+    # read directly with the offset and length pairs.
+    common.ZipWrite(output_zip, self.payload_file, arcname=payload_arcname,
+                    compress_type=zipfile.ZIP_STORED)
+    common.ZipWrite(output_zip, self.payload_properties,
+                    arcname=payload_properties_arcname,
+                    compress_type=zipfile.ZIP_STORED)
+
+
+class StreamingPropertyFiles(PropertyFiles):
+  """A subclass for computing the property-files for streaming A/B OTAs."""
+
+  def __init__(self):
+    super(StreamingPropertyFiles, self).__init__()
+    self.name = 'ota-streaming-property-files'
+    self.required = (
+        # payload.bin and payload_properties.txt must exist.
+        'payload.bin',
+        'payload_properties.txt',
+    )
+    self.optional = (
+        # apex_info.pb isn't directly used in the update flow
+        'apex_info.pb',
+        # care_map is available only if dm-verity is enabled.
+        'care_map.pb',
+        'care_map.txt',
+        # compatibility.zip is available only if target supports Treble.
+        'compatibility.zip',
+    )
+
+
+class AbOtaPropertyFiles(StreamingPropertyFiles):
+  """The property-files for A/B OTA that includes payload_metadata.bin info.
+
+  Since P, we expose one more token (aka property-file), in addition to the ones
+  for streaming A/B OTA, for a virtual entry of 'payload_metadata.bin'.
+  'payload_metadata.bin' is the header part of a payload ('payload.bin'), which
+  doesn't exist as a separate ZIP entry, but can be used to verify if the
+  payload can be applied on the given device.
+
+  For backward compatibility, we keep both of the 'ota-streaming-property-files'
+  and the newly added 'ota-property-files' in P. The new token will only be
+  available in 'ota-property-files'.
+  """
+
+  def __init__(self):
+    super(AbOtaPropertyFiles, self).__init__()
+    self.name = 'ota-property-files'
+
+  def _GetPrecomputed(self, input_zip):
+    offset, size = self._GetPayloadMetadataOffsetAndSize(input_zip)
+    return ['payload_metadata.bin:{}:{}'.format(offset, size)]
+
+  @staticmethod
+  def _GetPayloadMetadataOffsetAndSize(input_zip):
+    """Computes the offset and size of the payload metadata for a given package.
+
+    (From system/update_engine/update_metadata.proto)
+    A delta update file contains all the deltas needed to update a system from
+    one specific version to another specific version. The update format is
+    represented by this struct pseudocode:
+
+    struct delta_update_file {
+      char magic[4] = "CrAU";
+      uint64 file_format_version;
+      uint64 manifest_size;  // Size of protobuf DeltaArchiveManifest
+
+      // Only present if format_version > 1:
+      uint32 metadata_signature_size;
+
+      // The Bzip2 compressed DeltaArchiveManifest
+      char manifest[metadata_signature_size];
+
+      // The signature of the metadata (from the beginning of the payload up to
+      // this location, not including the signature itself). This is a
+      // serialized Signatures message.
+      char medatada_signature_message[metadata_signature_size];
+
+      // Data blobs for files, no specific format. The specific offset
+      // and length of each data blob is recorded in the DeltaArchiveManifest.
+      struct {
+        char data[];
+      } blobs[];
+
+      // These two are not signed:
+      uint64 payload_signatures_message_size;
+      char payload_signatures_message[];
+    };
+
+    'payload-metadata.bin' contains all the bytes from the beginning of the
+    payload, till the end of 'medatada_signature_message'.
+    """
+    payload_info = input_zip.getinfo('payload.bin')
+    (payload_offset, payload_size) = GetZipEntryOffset(input_zip, payload_info)
+
+    # Read the underlying raw zipfile at specified offset
+    payload_fp = input_zip.fp
+    payload_fp.seek(payload_offset)
+    header_bin = payload_fp.read(24)
+
+    # network byte order (big-endian)
+    header = struct.unpack("!IQQL", header_bin)
+
+    # 'CrAU'
+    magic = header[0]
+    assert magic == 0x43724155, "Invalid magic: {:x}, computed offset {}" \
+        .format(magic, payload_offset)
+
+    manifest_size = header[2]
+    metadata_signature_size = header[3]
+    metadata_total = 24 + manifest_size + metadata_signature_size
+    assert metadata_total < payload_size
+
+    return (payload_offset, metadata_total)