[Mailman-Developers] Signed Mailing Lists

[Abhilash Raj]

Hi all,

I worked in GSoC 2013 (thanks to Steve and Barry!) to add support for
verification and re-signing of emails in mailman3. I am working on the
branch to rebase it with the recent changes in the trunk and make it
ready to be merged. The reason for this post is to discuss about the
current feature set and possible enhancements/changes to it (which
probably was not included in my proposal due to time-limit of 3 months).

* A new `signature` rule checks for validity and age of the signature in
all the emails and appropriate action is taken according to the
configuration variable `default_badsignature_action` which can also be
configured from postorius.

* For now, I have added this rule to the default pipeline which may or
may not be desirable. I think if someone wants to accept unsigned emails
as well, one can set `default_badsignature_action` to always `accept`.
Thoughts on this?

* Each list has a public/private key pair that can be generated from
Postorius, the public is displayed in ascii-armor on the `list-summary`
page on the postorius from which it can be imported. I think would be
easy to just publish the public key to a keyserver (not implemented yet).

* Users can import their public key from the keyservers (just paste your
key-id and hit import) or by copy-pasting the ascii-armor'ed format in
postorius.

* A `signmessage` handler signs the email using its own private key (yes
even those which are already signed). The structure of the email was
decided so that both the signatures can be verified with maximum *unix
based mail-clients. I tested with notmuch, mu4e, claws-mail, thunderbird
(was able to verify the outermost signature iirc, but not the inner one
i.e. by the actual sender). The structure is of this form:


multipart/signed
    multipart/mixed
       multipart/signed
           text/plain
           application/pgp-signature
       text/plain
    application/pgp-signature

For other structures that I tested with refer this[1] post.

* For now all the outgoing messages are signed by default. Is a setting
required to make this optional?


Anything else that could be added or changed in this implementation?


[1]: http://asynchronous.in/2013/09/12/message-structure/
-- 
thanks,
Abhilash Raj

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