merge #451 - Increase DKIM key length to 2048

CHANGELOG.md

@@ -4,6 +4,9 @@ CHANGELOG
 In Development
 --------------
 
+Advisories:
+* This update replaces your DKIM signing key with a stronger key. Because of DNS caching/propagation, mail sent within a few hours after this update could be marked as spam by recipients. If you use External DNS, you will need to update your DNS records.
+
 Mail:
 * Greylisting will now let some reputable senders pass through immediately.
 * Searching mail (via IMAP) will now be much faster using the dovecot lucene full text search plugin.
@@ -11,6 +14,7 @@ Mail:
 * Fix for deleting admin@ and postmaster@ addresses.
 * Roundcube is updated to version 1.1.2, plugins updated.
 * Exchange/ActiveSync autoconfiguration was not working on all devices (e.g. iPhone) because of a case-sensitive URL.
+* The DKIM signing key has been increased to 2048 bits, from 1024, replacing the existing key.
 
 Web:
 * 'www' subdomains now automatically redirect to their parent domain (but you'll need to install an SSL certificate).

management/dns_update.py

@@ -250,8 +250,8 @@ def build_zone(domain, all_domains, additional_records, www_redirect_domains, en
 	# Skip if the user has set a DKIM record already.
 	opendkim_record_file = os.path.join(env['STORAGE_ROOT'], 'mail/dkim/mail.txt')
 	with open(opendkim_record_file) as orf:
-		m = re.match(r'(\S+)\s+IN\s+TXT\s+\( "([^"]+)"\s+"([^"]+)"\s*\)', orf.read(), re.S)
-		val = m.group(2) + m.group(3)
+		m = re.match(r'(\S+)\s+IN\s+TXT\s+\( ((?:"[^"]+"\s+)+)\)', orf.read(), re.S)
+		val = "".join(re.findall(r'"([^"]+)"', m.group(2)))
 		if not has_rec(m.group(1), "TXT", prefix="v=DKIM1; "):
 			records.append((m.group(1), "TXT", val, "Recommended. Provides a way for recipients to verify that this machine sent @%s mail." % domain))
 
@@ -373,9 +373,16 @@ $TTL 1800           ; default time to live
 			zone += subdomain
 		zone += "\tIN\t" + querytype + "\t"
 		if querytype == "TXT":
-			value = value.replace('\\', '\\\\') # escape backslashes
-			value = value.replace('"', '\\"') # escape quotes
-			value = '"' + value + '"' # wrap in quotes
+			# Divide into 255-byte max substrings.
+			v2 = ""
+			while len(value) > 0:
+				s = value[0:255]
+				value = value[255:]
+				s = s.replace('\\', '\\\\') # escape backslashes
+				s = s.replace('"', '\\"') # escape quotes
+				s = '"' + s + '"' # wrap in quotes
+				v2 += s + " "
+			value = v2
 		zone += value + "\n"
 
 	# DNSSEC requires re-signing a zone periodically. That requires

setup/dkim.sh

@@ -35,13 +35,18 @@ RequireSafeKeys         false
 EOF
 fi
 
-# Create a new DKIM key. This creates
-# mail.private and mail.txt in $STORAGE_ROOT/mail/dkim. The former
-# is the actual private key and the latter is the suggested DNS TXT
-# entry which we'll want to include in our DNS setup.
+# Create a new DKIM key. This creates mail.private and mail.txt
+# in $STORAGE_ROOT/mail/dkim. The former is the private key and
+# the latter is the suggested DNS TXT entry which we'll include
+# in our DNS setup. Note tha the files are named after the
+# 'selector' of the key, which we can change later on to support
+# key rotation.
+#
+# A 1024-bit key is seen as a minimum standard by several providers
+# such as Google. But they and others use a 2048 bit key, so we'll
+# do the same. Keys beyond 2048 bits may exceed DNS record limits.
 if [ ! -f "$STORAGE_ROOT/mail/dkim/mail.private" ]; then
-	# Should we specify -h rsa-sha256?
-	opendkim-genkey -r -s mail -D $STORAGE_ROOT/mail/dkim
+	opendkim-genkey -b 2048 -r -s mail -D $STORAGE_ROOT/mail/dkim
 fi
 
 # Ensure files are owned by the opendkim user and are private otherwise.

setup/migrate.py

@@ -95,6 +95,11 @@ def migration_7(env):
 	# Save.
 	conn.commit()
 
+def migration_8(env):
+	# Delete DKIM keys. We had generated 1024-bit DKIM keys.
+	# By deleting the key file we'll automatically generate
+	# a new key, which will be 2048 bits.
+	os.unlink(os.path.join(env['STORAGE_ROOT'], 'mail/dkim/mail.private'))
 
 def get_current_migration():
 	ver = 0