Re: MML, message-send-hook and automatically GnuPG-signing messages.

[Florian Weimer <fw@s.netic.de>]

Jonas Steverud <d4jonas@dtek.chalmers.se> writes:

> I use mc-bbdb.el to automatically encrypt to some people (using
> Mailcrypt and depening on what a special field in the BBDB is saying)
> and this adds mc-bbdb-auto-encrypt-send to message-send-hook. I also
> had until just recently

> What is the best way of solving this?
> 
> 1. Force evaluate MML before my encryption (either by hand or by
>    adding something to message-send-hook). Kludge?
> 
> 2. Add the sign/encrypt parts *after* the MML evaluation, but how is
>    this done? I think this is preferred since encryption and signing
>    should go after all other mail processing is finished and right
>    before the mail actually goes away.

3.  Use `mml-generate-multipart-alist'. Example (untested with current
    Gnus version):

(setq mml-generate-multipart-alist
  '(("signed" . rfc2015-generate-signed-multipart)
    ("encrypted" . rfc2015-generate-encrypted-multipart)))

(defun rfc2015-generate-enclosed-parts-and-funcall (cont func)
  "Generate the the parts in a temporary buffer and call FUNC.
Returns the result of FUNC."
  ;; Descend one level.
  (setq cont (cddr cont))
  (if (> (length cont) 1)
      ;; multipart/signed may not to contain more than one part.
      ;; Add an intermediate multipart/mixed if necessary.
      (setq cont (append '(multipart (type . "mixed")) cont))
    ;; Descend to the contained part.
    (setq cont (car cont)))
  ;; Generate contained parts and signature.  Do not include the
  ;; enclosing MIME boundaries in the signature.
  (with-temp-buffer
    ;; Generate subparts.
    (mml-generate-mime-1 cont)
    ;; Make sure that last line ends with <LF>.
    (goto-char (point-max))
    (unless (bolp)
      (insert "\n"))
    (funcall func)))

(defun rfc2015-generate-signed-multipart (cont)
  (let* ((mml-boundary (mml-compute-boundary cont))
         ;; Make sure that the enclosed parts are encoded in the safest way.
         (quoted-printable-encode-from t)
         (mm-encode-no-7/8bit t)
         (parts-and-signature
          (rfc2015-generate-enclosed-parts-and-funcall
           cont
           (lambda ()
             (cons 
              (buffer-string)
              (rfc2015-gpg-sign (current-buffer))))))
         (parts (car parts-and-signature))
         (signature (cdr parts-and-signature)))
    (insert (format "Content-Type: multipart/signed; boundary=\"%s\";\n"
                    mml-boundary)
            "\tmicalg=pgp-md5; protocol=\"application/pgp-signature\"\n"
            "\n"
            "\n--" mml-boundary "\n")
    ;; Insert generated parts and signature.
    (insert parts)
    (insert "\n--" mml-boundary "\n"
            "Content-Type: application/pgp-signature\n"
            "\n"
            signature
            "\n--" mml-boundary "--\n")))

(defun rfc2015-generate-encrypted-multipart (cont)
  (let* ((mml-boundary (mml-compute-boundary cont))
         (encrypted-parts
          (rfc2015-generate-enclosed-parts-and-funcall
           cont
           (lambda ()
             (rfc2015-gpg-encrypt)
             (buffer-string)))))
    (insert (format "Content-Type: multipart/encrypted; boundary=\"%s\";\n"
                    mml-boundary)
            "\tprotocol=\"application/pgp-encrypted\"\n"
            "\n"
            "\n--" mml-boundary "\n"
            "Content-Type: application/pgp-encrypted\n"
            "\n"
            "Version: 1\n")
    (insert "\n--" mml-boundary "\n"
            "Content-Type: application/octet-stream\n"
            "\n"
            encrypted-parts
            "\n--" mml-boundary "\n")))