leading dot causes wrong signature

[Stefan Krause]

Hi,

found a serious error causing a miscalculated hash.

If any line from body starts with a dot (.), mail signing ends with a wrong signature.

You can test this with the following commands.

working:
echo "message text" | mail -s "Testmail" <email address hidden> -f <email address hidden>
printf "Subject: Testmail\n\nmessage text" | <email address hidden> -f <email address hidden>

causing error:
echo ".message text" | mail -s "Testmail" <email address hidden> -f <email address hidden>
printf "Subject: Testmail\n\n.message text" | <email address hidden> -f <email address hidden>

Reproduced the error with opensmtpd/jammy,now 6.8.0p2 on Ubuntu 22.04.3 LTS and opensmtpd-6.8.0,1 on FreeBSD 12.4.

Could you please fix this the problem?

Kind regards

Stefan

[Stefan Krause (krauses)]

After some further research the problem is not related to dkimpy!

http://www.opendkim.org/libopendkim/dkim_body.html
"Dot stuffing and the terminating dot in the message body are expected to be removed by the caller." see the notes

openSMTPD masks a leading dot with an additional dot, which is a correct behaviour according to RFC.
https://www.rfc-editor.org/rfc/rfc5321#section-4.5.2

The problem was caused by the used OpenSMTPD -> dkimpy integration.
https://gist.github.com/palant/c6ad869a1dd2cd79506898e4e8401438