initial commit

update-dkim.py

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+#!/usr/bin/env python3
+#
+# 
+# This script takes two arguments: 
+#  1) a BIND DNS zone file
+#  2) a DNS record generated by 'opendkim-genkey'
+#
+# 'opendkim-genkey' is part of the 'opendkim-tools' Debian package
+#
+# This script use regex to 
+#  1) extract the DKIM selector and the value of the TXT record from the
+#     DKIM TXT record generated by opendkim-genkey
+#  2) replace the DKIM selector and TXT value in the zone file with the
+#     new values
+#
+#  Example:
+#  First run:
+#   /usr/sbin/opendkim-genkey -b 2048 -d example.org -s $(/bin/date +%Y%m%d)-1
+#  which will generate a DNS DKIM TXT record such as '20210811-1.txt'
+#  Then run this script, passing the zone file you want to update and the above
+#    .txt file:
+#   update-dkim.py <zone file> 20210811-1.txt
+#
+
+import sys
+
+# Make sure Python is at least version 3.6 (required for f-string literals support)
+if not (sys.version_info.major == 3 and sys.version_info.minor >= 6):
+    print("This script requires Python 3.6 or higher")
+    print("You are using Python {}.{}.".format(sys.version_info.major, sys.version_info.minor))
+    sys.exit(1)
+
+import argparse
+import re
+
+# Create an ArgumentParser object to parse the command-line arguments
+parser = argparse.ArgumentParser(
+    description='Update DNS zone file DKIM TXT record(s)'
+)
+
+# First argument is the zone file which will be updated    
+parser.add_argument(
+    'zone_file', type=argparse.FileType('r+')
+)
+    
+# Second argument is the opendkim-genkey-generated DKIM TXT record
+parser.add_argument(
+    'dkim_txt', type=argparse.FileType('r')
+)
+
+args = parser.parse_args()
+
+# Read the files into corresponding string variables
+zone_text = args.zone_file.read()
+dkim_txt = args.dkim_txt.read()
+
+# This regex strips the old DKIM selector and TXT value from the zone file
+# The remaining text is captured in a backreference
+zone_re = re.compile(
+    r'^[\d-]+(\._domainkey\.?[a-z.]*\s+[0-9h]+\s+IN\s+TXT\s+\()[\s"=;+\/\w]+',
+    re.MULTILINE
+)
+
+# This regex uses two backreferences to capture the DKIM selector and TXT value
+#  from the opendkim-genkey-generated DKIM record
+dkim_txt_re = re.compile(
+    r'^([\d-]+)\._domainkey\s+IN\s+TXT\s+\(([\s"=;+\/\w]+).+\s+$',
+    re.MULTILINE
+)
+
+# Store the captured values as variables
+selector = dkim_txt_re.sub(r'\1', dkim_txt)
+dkim_value = dkim_txt_re.sub(r'\2', dkim_txt)
+
+# Perform the regex substitution on the zone file
+#  use f-strings to provide the variables in the substitution
+zone = zone_re.sub(rf"{selector}\1{dkim_value}", zone_text)
+
+# print("\nselector: ", selector, "\ndkim_value: ", dkim_value, "\n\nzone:\n", zone)
+print(zone)
+
+# Sample DKIM TXT record
+#
+# 20160525-014646._domainkey.whitehall 3h IN TXT ( "v=DKIM1; k=rsa; t=y; p=MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCA"
+#     "QEAulkdTaAsWGpcN4O6HRMzCN6i67AWoMyjemrryvd+j/2epCSZ3qNfkD/ZV8g4S"
+#     "42IVk4dBs3evQQCyCGQhhoqpQIDAQAB" )
+