Move some OTA signing functions to a separte file

This makes it easier for other otatools to re-use these logic without
having to pull in lots of dependencies.

Test: th
Bug: 227848550

Change-Id: I81ed01c5cea4b934a074650731b6f89752221de9

tools/releasetools/payload_signer.py

@@ -0,0 +1,89 @@
+#!/usr/bin/env python3
+#
+# Copyright (C) 2022 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 common
+import logging
+from common import OPTIONS
+
+logger = logging.getLogger(__name__)
+
+
+class PayloadSigner(object):
+  """A class that wraps the payload signing works.
+
+  When generating a Payload, hashes of the payload and metadata files will be
+  signed with the device key, either by calling an external payload signer or
+  by calling openssl with the package key. This class provides a unified
+  interface, so that callers can just call PayloadSigner.Sign().
+
+  If an external payload signer has been specified (OPTIONS.payload_signer), it
+  calls the signer with the provided args (OPTIONS.payload_signer_args). Note
+  that the signing key should be provided as part of the payload_signer_args.
+  Otherwise without an external signer, it uses the package key
+  (OPTIONS.package_key) and calls openssl for the signing works.
+  """
+
+  def __init__(self, package_key=None, private_key_suffix=None, pw=None, payload_signer=None):
+    if package_key is None:
+      package_key = OPTIONS.package_key
+    if private_key_suffix is None:
+      private_key_suffix = OPTIONS.private_key_suffix
+
+    if payload_signer is None:
+      # Prepare the payload signing key.
+      private_key = package_key + private_key_suffix
+
+      cmd = ["openssl", "pkcs8", "-in", private_key, "-inform", "DER"]
+      cmd.extend(["-passin", "pass:" + pw] if pw else ["-nocrypt"])
+      signing_key = common.MakeTempFile(prefix="key-", suffix=".key")
+      cmd.extend(["-out", signing_key])
+      common.RunAndCheckOutput(cmd, verbose=True)
+
+      self.signer = "openssl"
+      self.signer_args = ["pkeyutl", "-sign", "-inkey", signing_key,
+                          "-pkeyopt", "digest:sha256"]
+      self.maximum_signature_size = self._GetMaximumSignatureSizeInBytes(
+          signing_key)
+    else:
+      self.signer = payload_signer
+      self.signer_args = OPTIONS.payload_signer_args
+      if OPTIONS.payload_signer_maximum_signature_size:
+        self.maximum_signature_size = int(
+            OPTIONS.payload_signer_maximum_signature_size)
+      else:
+        # The legacy config uses RSA2048 keys.
+        logger.warning("The maximum signature size for payload signer is not"
+                       " set, default to 256 bytes.")
+        self.maximum_signature_size = 256
+
+  @staticmethod
+  def _GetMaximumSignatureSizeInBytes(signing_key):
+    out_signature_size_file = common.MakeTempFile("signature_size")
+    cmd = ["delta_generator", "--out_maximum_signature_size_file={}".format(
+        out_signature_size_file), "--private_key={}".format(signing_key)]
+    common.RunAndCheckOutput(cmd, verbose=True)
+    with open(out_signature_size_file) as f:
+      signature_size = f.read().rstrip()
+    logger.info("%s outputs the maximum signature size: %s", cmd[0],
+                signature_size)
+    return int(signature_size)
+
+  def Sign(self, in_file):
+    """Signs the given input file. Returns the output filename."""
+    out_file = common.MakeTempFile(prefix="signed-", suffix=".bin")
+    cmd = [self.signer] + self.signer_args + ['-in', in_file, '-out', out_file]
+    common.RunAndCheckOutput(cmd)
+    return out_file