[Djigzo users] Notify about a successfully complete for signcheck

Martijn Brinkers martijn at djigzo.com
Thu Oct 27 10:32:06 CEST 2011


On 10/27/2011 09:25 AM, matthiasdort wrote:
>>>  I guess something like a "[Signed]" tag in the subject to show the end 
>>> user (internal recipient) that the message was signed and could be 
>>> verified when hitting the Djigzo Gateway.
>>
>>  
>>
>>  Thank you Andreas, yes, this is exactly what i mean.

This is not (yet?) supported. The main question is where are you using
the tag for? The reason I'm asking is that a tag line can lead to a
false sense of security. For example suppose an external sender sends a
non-signed message that contains the tag [Signed] in the subject?
You might argue that all incoming email should be scanned for such a tag
and have the tag be removed. Ok, then what about [ signed ]? Again you
might argue that the scanning should work on a regular expression and
should skip all spaces. Ok, then I come up with the following example,
{Signed}, or just Signed, or Signd.
Just as long as your end-users just use the tag as an indication that
the message *might* be signed, this should not be a problem. The problem
starts when end-users *assume* the message is signed and trusted because
the subject contains some kind of tag.

The best way to detect whether a message is signed and is trusted is by
using an S/MIME capable email client. If however you are not using an
S/MIME capable email client or are stripping the S/MIME signatures this
won't help. The gateway will however add certain header fields which
indicate whether the email is signed and whether the signature was
trusted/valid etc. Appendix A of the "S/MIME setup guide" briefly
explains these headers. Since all X-Djigzo-* headers are removed from
any incoming email, those headers cannot be spoofed. The trouble however
with these headers is that it's hard for end-users to read and interpret.

To conclude, I'm not saying that adding some kind of keyword/tag to the
subject should never be done. But, you should be careful on what it
means for your end-users when the subject contains a certain keyword/tag.

What is currently missing is a mailet (a mailet is a small piece of
software that handles an email)  that can add something to the current
subject of a message. I will add this to the todo list. If such a mailet
is available, you can add this functionality to the xml mail flow
specification and match when the email contains the keywords. This might
actually be done with Postfix as a workaround.

One last question, is there a reason you cannot use an S/MIME email
client to check the signatures?

Kind regards,

Martijn Brinkers

-- 
Djigzo open source email encryption



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