diff --git a/apex/replace_bytes.py b/apex/replace_bytes.py
new file mode 100644
index 0000000..b22f132
--- /dev/null
+++ b/apex/replace_bytes.py
@@ -0,0 +1,72 @@
+#!/usr/bin/env python
+#
+# Copyright (C) 2021 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.
+"""replace_bytes is a command line tool to replace bytes in a file.
+
+Typical usage: replace_bytes target_file old_file new_file
+
+  replace bytes of old_file with bytes of new_file in target_file. old_file and new_file should be
+  the same size.
+
+"""
+import argparse
+import sys
+
+
+def ParseArgs(argv):
+    parser = argparse.ArgumentParser(description='Replace bytes')
+    parser.add_argument(
+        'target_file',
+        help='path to the target file.')
+    parser.add_argument(
+        'old_file',
+        help='path to the file containing old bytes')
+    parser.add_argument(
+        'new_file',
+        help='path to the file containing new bytes')
+    return parser.parse_args(argv)
+
+
+def ReplaceBytes(target_file, old_file, new_file):
+    # read old bytes
+    with open(old_file, 'rb') as f:
+        old_bytes = f.read()
+
+    # read new bytes
+    with open(new_file, 'rb') as f:
+        new_bytes = f.read()
+
+    assert len(old_bytes) == len(new_bytes), 'Pubkeys should be the same size. (%d != %d)' % (
+        len(old_bytes), len(new_bytes))
+
+    # replace bytes in target_file
+    with open(target_file, 'r+b') as f:
+        pos = f.read().find(old_bytes)
+        assert pos != -1, 'Pubkey not found'
+        f.seek(pos)
+        f.write(new_bytes)
+
+
+def main(argv):
+    try:
+        args = ParseArgs(argv)
+        ReplaceBytes(args.target_file, args.old_file, args.new_file)
+    except Exception as e:
+        print(e)
+        sys.exit(1)
+
+
+if __name__ == '__main__':
+    main(sys.argv[1:])