getdkimselector

#!/usr/bin/python3
#
# WARNING: Script is now developed in the keymonitor repository and will soon be removed here:
# https://github.com/badkeys/keymonitor/blob/main/dkim/getdkimselector

import argparse
import email.parser
import mailbox
import os

allheaders = [
    "DKIM-Signature",
    "ARC-Seal",
    "ARC-Message-Signature",
    "X-Google-DKIM-Signature",
    "X-Original-DKIM-Signature",
    "DomainKey-Signature",
]


def parse_mail(em):
    for xheader in allheaders:
        sigs = em.get_all(xheader)
        if sigs is None:
            continue
        for header in sigs:
            sig = str(header)
            sig = sig.translate({ord(c): None for c in "\n\r\t "})
            dkim = {}
            for f in sig.split(";"):
                fs = f.split("=", 2)
                if len(fs) != 2:
                    continue
                dkim[fs[0]] = fs[1]
            if args.verbose:
                print(sig)
                print(dkim)
            if ("d" not in dkim) or ("s" not in dkim):
                # looks invalid
                continue
            if (dkim["s"] == "") or (dkim["s"].isascii() is False):
                continue
            newhost = f"{dkim['s']}._domainkey.{dkim['d']}"
            if newhost not in hosts:
                hosts.add(newhost)
                print(newhost)


ap = argparse.ArgumentParser()
ap.add_argument("paths", nargs="+")
ap.add_argument("-v", "--verbose", action="store_true")
ap.add_argument("-m", "--mbox", action="store_true")
args = ap.parse_args()

hosts = set()
for path in args.paths:
    for root, _, files in os.walk(path):
        for name in files:
            fn = os.path.join(root, name)

            if args.mbox:
                mb = mailbox.mbox(fn)
                try:
                    for m in mb.iteritems():
                        parse_mail(m[1])
                except UnicodeDecodeError:
                    pass

            else:  # maildir mode
                with open(fn, "rb") as fp:
                    try:
                        parse_mail(email.message_from_binary_file(fp))
                    except Exception as e:
                        print(f"Something went wrong while parsing {fn}")
                        print(e)