[Users] nonASCII chars in OpenPGP signature

[Michael Hughes]

On Sat, 16 Apr 2022 14:02:04 +0200
Slavko <linux at slavino.sk> wrote:

> Hi,
> 
> recently i got one mail which i wrote in CM rejected with message:
> 
>     550 5.6.0 improper use of 8-bit data in message header
> 
> As the message was attached in bounce, i inspect it, and only
> suspicious message's headers i found is Content-Description: in
> OpenPGP signature:
> 
>     Content-Type: application/pgp-signature
>     Content-Description: Digitálny podpis OpenPGP
> 
> (raw translated "OpenPGP digital signature")
> 
> As one can see, it contains nonASCII char -- the "á", but the message
> itself (nor that signature) has not Content-Transfer-Encoding:
> defined, which AFAIK defaults to 7bit. I sign all outgoing messages
> for years, and i meet this problem first time, but as it was working
> i never inspect outgoing message encoding, thus i cannot tell if and
> when it was changed.
> 
> The guess about signature problem is near to 100% right, as when i
> resend that message not signed, it was accepted. The recipient's MTA
> is postfix and i read, that postfix's 8BITMIME/SMTPUTF8
> implementation is prone to be badly configured, and target system
> advertise 8BITMIME (only), thus i do not know if that matter (i never
> used postfix, i only fight with similar problem with Subject: but
> that was not CM related).
> 
> Now i am not sure what i want to ask ;-) But that comes in my minds is
> if that signature's "Content-Description:" header was added by CM or
> by gnupg? If it is added by CM, why is not 8bit transfer encoding
> used?
> 
> Is it possible to force message's Content-Transfer-Encoding: 8bit in
> CM? Or how i can ensure, that message content fits its transfer
> encoding?
> 
> regards
> 
> -- 
> Slavko
> https://www.slavino.sk

The email to the list also fails the DKIM check with OpenDKIM on my
system:

KIM-Filter: OpenDKIM Filter v2.10.3 thehugheslogcabin.net 23GCA1xo071267
Authentication-Results: thehugheslogcabin.net;
	dkim=fail reason="signature verification failed" (1024-bit key) header.d=slavino.sk header.i=@slavino.sk header.b=K0kj2xsf;
	dkim=permerror (0-bit key) header.d=slavino.sk header.i=@slavino.sk header.b=pAQIN/0F
Authentication-Results:  perfora.net; dkim=fail header.i=@slavino.sk

-- 
Michael Hughes
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