diff --git a/tools/releasetools/ota_from_target_files.py b/tools/releasetools/ota_from_target_files.py
index 2b64f7f..edc20f6 100755
--- a/tools/releasetools/ota_from_target_files.py
+++ b/tools/releasetools/ota_from_target_files.py
@@ -360,6 +360,122 @@
     return out_file
 
 
+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'
+
+  def __init__(self):
+    # The place where the output from the subprocess should go.
+    self._log_file = sys.stdout if OPTIONS.verbose else subprocess.PIPE
+    self.payload_file = None
+    self.payload_properties = None
+
+  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])
+    cmd.extend(additional_args)
+    p = common.Run(cmd, stdout=self._log_file, stderr=subprocess.STDOUT)
+    stdoutdata, _ = p.communicate()
+    assert p.returncode == 0, \
+        "brillo_update_payload generate failed: {}".format(stdoutdata)
+
+    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", "256",
+           "--metadata_hash_file", metadata_sig_file,
+           "--payload_hash_file", payload_sig_file]
+    p1 = common.Run(cmd, stdout=self._log_file, stderr=subprocess.STDOUT)
+    p1.communicate()
+    assert p1.returncode == 0, "brillo_update_payload hash failed"
+
+    # 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", "256",
+           "--metadata_signature_file", signed_metadata_sig_file,
+           "--payload_signature_file", signed_payload_sig_file]
+    p1 = common.Run(cmd, stdout=self._log_file, stderr=subprocess.STDOUT)
+    p1.communicate()
+    assert p1.returncode == 0, "brillo_update_payload sign failed"
+
+    # 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]
+    p1 = common.Run(cmd, stdout=self._log_file, stderr=subprocess.STDOUT)
+    p1.communicate()
+    assert p1.returncode == 0, "brillo_update_payload properties failed"
+
+    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
+
+    # 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.PAYLOAD_BIN,
+                    compress_type=zipfile.ZIP_STORED)
+    common.ZipWrite(output_zip, self.payload_properties,
+                    arcname=Payload.PAYLOAD_PROPERTIES_TXT,
+                    compress_type=zipfile.ZIP_STORED)
+
+
 def SignOutput(temp_zip_name, output_zip_name):
   pw = OPTIONS.key_passwords[OPTIONS.package_key]
 
@@ -1122,12 +1238,6 @@
       value += ' ' * (expected_length - len(value))
     return value
 
-  # The place where the output from the subprocess should go.
-  log_file = sys.stdout if OPTIONS.verbose else subprocess.PIPE
-
-  # Get the PayloadSigner to be used in step 3.
-  payload_signer = PayloadSigner()
-
   # Stage the output zip package for package signing.
   temp_zip_file = tempfile.NamedTemporaryFile()
   output_zip = zipfile.ZipFile(temp_zip_file, "w",
@@ -1143,77 +1253,23 @@
   # Metadata to comply with Android OTA package format.
   metadata = GetPackageMetadata(target_info, source_info)
 
-  # 1. Generate payload.
-  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])
+  # Generate payload.
+  payload = Payload()
+
+  # Enforce a max timestamp this payload can be applied on top of.
   if OPTIONS.downgrade:
     max_timestamp = source_info.GetBuildProp("ro.build.date.utc")
   else:
     max_timestamp = metadata["post-timestamp"]
-  cmd.extend(["--max_timestamp", max_timestamp])
-  p1 = common.Run(cmd, stdout=log_file, stderr=subprocess.STDOUT)
-  p1.communicate()
-  assert p1.returncode == 0, "brillo_update_payload generate failed"
+  additional_args = ["--max_timestamp", max_timestamp]
 
-  # 2. 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", payload_file,
-         "--signature_size", "256",
-         "--metadata_hash_file", metadata_sig_file,
-         "--payload_hash_file", payload_sig_file]
-  p1 = common.Run(cmd, stdout=log_file, stderr=subprocess.STDOUT)
-  p1.communicate()
-  assert p1.returncode == 0, "brillo_update_payload hash failed"
+  payload.Generate(target_file, source_file, additional_args)
 
-  # 3. Sign the hashes and insert them back into the payload file.
-  # 3a. Sign the payload hash.
-  signed_payload_sig_file = payload_signer.Sign(payload_sig_file)
+  # Sign the payload.
+  payload.Sign(PayloadSigner())
 
-  # 3b. Sign the metadata hash.
-  signed_metadata_sig_file = payload_signer.Sign(metadata_sig_file)
-
-  # 3c. 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", payload_file,
-         "--payload", signed_payload_file,
-         "--signature_size", "256",
-         "--metadata_signature_file", signed_metadata_sig_file,
-         "--payload_signature_file", signed_payload_sig_file]
-  p1 = common.Run(cmd, stdout=log_file, stderr=subprocess.STDOUT)
-  p1.communicate()
-  assert p1.returncode == 0, "brillo_update_payload sign failed"
-
-  # 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]
-  p1 = common.Run(cmd, stdout=log_file, stderr=subprocess.STDOUT)
-  p1.communicate()
-  assert p1.returncode == 0, "brillo_update_payload properties failed"
-
-  if OPTIONS.wipe_user_data:
-    with open(properties_file, "a") as f:
-      f.write("POWERWASH=1\n")
-
-  # Add the signed payload file and properties into the zip. In order to
-  # support streaming, we pack payload.bin, payload_properties.txt and
-  # care_map.txt as ZIP_STORED. So these entries can be read directly with
-  # the offset and length pairs.
-  common.ZipWrite(output_zip, signed_payload_file, arcname="payload.bin",
-                  compress_type=zipfile.ZIP_STORED)
-  common.ZipWrite(output_zip, properties_file,
-                  arcname="payload_properties.txt",
-                  compress_type=zipfile.ZIP_STORED)
+  # Write the payload into output zip.
+  payload.WriteToZip(output_zip)
 
   # If dm-verity is supported for the device, copy contents of care_map
   # into A/B OTA package.
@@ -1224,6 +1280,8 @@
     namelist = target_zip.namelist()
     if care_map_path in namelist:
       care_map_data = target_zip.read(care_map_path)
+      # In order to support streaming, care_map.txt needs to be packed as
+      # ZIP_STORED.
       common.ZipWriteStr(output_zip, "care_map.txt", care_map_data,
                          compress_type=zipfile.ZIP_STORED)
     else:
diff --git a/tools/releasetools/test_ota_from_target_files.py b/tools/releasetools/test_ota_from_target_files.py
index fa6655b..103d4b6 100644
--- a/tools/releasetools/test_ota_from_target_files.py
+++ b/tools/releasetools/test_ota_from_target_files.py
@@ -15,12 +15,14 @@
 #
 
 import copy
+import os
 import os.path
 import unittest
+import zipfile
 
 import common
 from ota_from_target_files import (
-    _LoadOemDicts, BuildInfo, GetPackageMetadata, PayloadSigner,
+    _LoadOemDicts, BuildInfo, GetPackageMetadata, Payload, PayloadSigner,
     WriteFingerprintAssertion)
 
 
@@ -564,3 +566,157 @@
 
     verify_file = os.path.join(self.testdata_dir, self.SIGNED_SIGFILE)
     self._assertFilesEqual(verify_file, signed_file)
+
+
+class PayloadTest(unittest.TestCase):
+
+  def setUp(self):
+    self.testdata_dir = get_testdata_dir()
+    self.assertTrue(os.path.exists(self.testdata_dir))
+
+    common.OPTIONS.wipe_user_data = False
+    common.OPTIONS.payload_signer = None
+    common.OPTIONS.payload_signer_args = None
+    common.OPTIONS.package_key = os.path.join(self.testdata_dir, 'testkey')
+    common.OPTIONS.key_passwords = {
+        common.OPTIONS.package_key : None,
+    }
+
+  def tearDown(self):
+    common.Cleanup()
+
+  @staticmethod
+  def _construct_target_files():
+    target_files = common.MakeTempFile(prefix='target_files-', suffix='.zip')
+    with zipfile.ZipFile(target_files, 'w') as target_files_zip:
+      # META/update_engine_config.txt
+      target_files_zip.writestr(
+          'META/update_engine_config.txt',
+          "PAYLOAD_MAJOR_VERSION=2\nPAYLOAD_MINOR_VERSION=4\n")
+
+      # META/ab_partitions.txt
+      ab_partitions = ['boot', 'system', 'vendor']
+      target_files_zip.writestr(
+          'META/ab_partitions.txt',
+          '\n'.join(ab_partitions))
+
+      # Create dummy images for each of them.
+      for partition in ab_partitions:
+        target_files_zip.writestr('IMAGES/' + partition + '.img',
+                                  os.urandom(len(partition)))
+
+    return target_files
+
+  def _create_payload_full(self):
+    target_file = self._construct_target_files()
+    payload = Payload()
+    payload.Generate(target_file)
+    return payload
+
+  def _create_payload_incremental(self):
+    target_file = self._construct_target_files()
+    source_file = self._construct_target_files()
+    payload = Payload()
+    payload.Generate(target_file, source_file)
+    return payload
+
+  def test_Generate_full(self):
+    payload = self._create_payload_full()
+    self.assertTrue(os.path.exists(payload.payload_file))
+
+  def test_Generate_incremental(self):
+    payload = self._create_payload_incremental()
+    self.assertTrue(os.path.exists(payload.payload_file))
+
+  def test_Generate_additionalArgs(self):
+    target_file = self._construct_target_files()
+    source_file = self._construct_target_files()
+    payload = Payload()
+    # This should work the same as calling payload.Generate(target_file,
+    # source_file).
+    payload.Generate(
+        target_file, additional_args=["--source_image", source_file])
+    self.assertTrue(os.path.exists(payload.payload_file))
+
+  def test_Generate_invalidInput(self):
+    target_file = self._construct_target_files()
+    common.ZipDelete(target_file, 'IMAGES/vendor.img')
+    payload = Payload()
+    self.assertRaises(AssertionError, payload.Generate, target_file)
+
+  def test_Sign_full(self):
+    payload = self._create_payload_full()
+    payload.Sign(PayloadSigner())
+
+    output_file = common.MakeTempFile(suffix='.zip')
+    with zipfile.ZipFile(output_file, 'w') as output_zip:
+      payload.WriteToZip(output_zip)
+
+    import check_ota_package_signature
+    check_ota_package_signature.VerifyAbOtaPayload(
+        os.path.join(self.testdata_dir, 'testkey.x509.pem'),
+        output_file)
+
+  def test_Sign_incremental(self):
+    payload = self._create_payload_incremental()
+    payload.Sign(PayloadSigner())
+
+    output_file = common.MakeTempFile(suffix='.zip')
+    with zipfile.ZipFile(output_file, 'w') as output_zip:
+      payload.WriteToZip(output_zip)
+
+    import check_ota_package_signature
+    check_ota_package_signature.VerifyAbOtaPayload(
+        os.path.join(self.testdata_dir, 'testkey.x509.pem'),
+        output_file)
+
+  def test_Sign_withDataWipe(self):
+    common.OPTIONS.wipe_user_data = True
+    payload = self._create_payload_full()
+    payload.Sign(PayloadSigner())
+
+    with open(payload.payload_properties) as properties_fp:
+      self.assertIn("POWERWASH=1", properties_fp.read())
+
+  def test_Sign_badSigner(self):
+    """Tests that signing failure can be captured."""
+    payload = self._create_payload_full()
+    payload_signer = PayloadSigner()
+    payload_signer.signer_args.append('bad-option')
+    self.assertRaises(AssertionError, payload.Sign, payload_signer)
+
+  def test_WriteToZip(self):
+    payload = self._create_payload_full()
+    payload.Sign(PayloadSigner())
+
+    output_file = common.MakeTempFile(suffix='.zip')
+    with zipfile.ZipFile(output_file, 'w') as output_zip:
+      payload.WriteToZip(output_zip)
+
+    with zipfile.ZipFile(output_file) as verify_zip:
+      # First make sure we have the essential entries.
+      namelist = verify_zip.namelist()
+      self.assertIn(Payload.PAYLOAD_BIN, namelist)
+      self.assertIn(Payload.PAYLOAD_PROPERTIES_TXT, namelist)
+
+      # Then assert these entries are stored.
+      for entry_info in verify_zip.infolist():
+        if entry_info.filename not in (Payload.PAYLOAD_BIN,
+                                       Payload.PAYLOAD_PROPERTIES_TXT):
+          continue
+        self.assertEqual(zipfile.ZIP_STORED, entry_info.compress_type)
+
+  def test_WriteToZip_unsignedPayload(self):
+    """Unsigned payloads should not be allowed to be written to zip."""
+    payload = self._create_payload_full()
+
+    output_file = common.MakeTempFile(suffix='.zip')
+    with zipfile.ZipFile(output_file, 'w') as output_zip:
+      self.assertRaises(AssertionError, payload.WriteToZip, output_zip)
+
+    # Also test with incremental payload.
+    payload = self._create_payload_incremental()
+
+    output_file = common.MakeTempFile(suffix='.zip')
+    with zipfile.ZipFile(output_file, 'w') as output_zip:
+      self.assertRaises(AssertionError, payload.WriteToZip, output_zip)