diff --git a/tools/pm3_key_file_diff.py b/tools/pm3_key_file_diff.py
new file mode 100755
index 000000000..4069d6684
--- /dev/null
+++ b/tools/pm3_key_file_diff.py
@@ -0,0 +1,80 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+
+########################################################################
+#
+# Copyright 2018 Gerhard Klostermeier
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+########################################################################
+#
+# Usage: ./key-file-diff.py <file A> <file B>
+#
+########################################################################
+#
+# Info:
+# - Read two key files and show the keys that are in file B but not in A.
+# - Keys must be 12 hex characters long and at the beginning of a line.
+#
+########################################################################
+
+
+import re
+
+
+def main(args):
+    """
+    Read two key files and show the keys that are in file B but not in A.
+    :param args: Path to two key files A and B (positional shell parameters).
+    :return: 0 if everything went fine.
+    """
+    key_file_a = args[1]
+    key_file_b = args[2]
+
+    with open(key_file_a, 'r') as f:
+        keys_a = parse_keys(f)
+    with open(key_file_b, 'r') as f:
+        keys_b = parse_keys(f)
+
+    # Show all keys that are in B but not in A.
+    keys_diff = keys_b.difference(keys_a)
+    for key in keys_diff:
+        print(key)
+
+    return 0
+
+
+def parse_keys(file):
+    """
+    Parse keys from a file and return them as a set.
+    Keys must be 12 hex characters long and at the beginning of a line.
+    :param file: Path to a file containing keys.
+    :return: A set of keys read from the file.
+    """
+    keys = set()
+    key_regex = re.compile('^[0-9a-fA-F]{12}')
+    for line in file:
+        key = key_regex.match(line)
+        try:
+            key = key.group(0).upper()
+            keys.add(key)
+        except AttributeError:
+            pass
+    return keys
+
+
+if __name__ == '__main__':
+    import sys
+    sys.exit(main(sys.argv))