From: Antoine =?utf-8?Q?Beaupr=C3=A9?= <anarcat@anarcat.ath.cx>
To: Gregor Zattler <telegraph@gmx.net>, David Edmondson <dme@dme.org>,
	Jameson Graef Rollins <jrollins@finestructure.net>,
	Gregor Zattler <telegraph@gmx.net>, Notmuch Mail <notmuch@notmuchmail.org>
Subject: Re: Emacs: Crypto: How to get automatic encryption?
In-Reply-To: <87d3akppoc.fsf@shi.workgroup>
Message-ID: <87pqejj5nl.fsf@marcos.anarcat.ath.cx>
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Date: Tue, 17 Jan 2012 04:48:36 -0000

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Jumping in here, I have modified the previously posted code here to
provide me with a more complete solution.

With the attach code, I can:

 * automatically encrypt mails if all recipients have a *valid* public
   key. The previous patch allowed encryption if a key existed but was
   revoked, which cause a weird UX issue where the user would be
   bothered with "No public key for..."

 * not have specify if i want to encrypt the mail or not: it is
   encrypted if possible

 * try to autodetect (by running the function directly) if the mail will
   be crypted and signed or just signed before sending

 * explicitely request the mail to be encrypted or just signed, if I
   want to, using the usual keybindings (ie. the existing #secure tags
   are respected)

So basically, this replaces the common hook:

(add-hook 'message-setup-hook 'mml-secure-sign-pgpmime)

with this:

(add-hook 'message-send-hook 'anarcat/message-set-encryption)

The rationale behind this technique is that the setup-hook runs when
recipients are not yet defined so it will always set the mail to be only
signed, even though your final recipients should be crypted.=20

An alternative would be for notmuch to prompt the To: header before
setting up the buffer ("=C3=A0 la" Mutt), but I didn't feel like going that
way.

Code is attached. Obviously, those function names would change if they
would be to integrate into notmuch. ;)


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;; -*- mode: emacs-lisp; -*-

(require 'notmuch)

(add-hook 'message-send-hook 'anarcat/message-set-encryption)

(defun anarcat/message-set-encryption (&optional force)
  "Automatically set the encryption depending on the recipients.

If ran interactively, will overwrite settings, otherwise it will
not touch existing settings, so that this can safely be ran in
`message-send-hook'."
  (interactive "p")
  (message-goto-body)
  ;; clear existing settings
  (if (and force (re-search-forward "<#secure [^>]*>\n" nil t))
      (replace-match "" nil nil))
  ;; If we can encrypt, do so, else just sign.
  (if (or force (not (re-search-forward "<#secure [^>]*>\n" nil t)))
      (if (anarcat/message-guess-encryption)
          (insert "<#secure method=3Dpgpmime mode=3Dsignencrypt>\n")
        (insert "<#secure method=3Dpgpmime mode=3Dsign>\n"))
    )
)

;; http://notmuchmail.org/pipermail/notmuch/2012/007340.html
(defun anarcat/message-guess-encryption ()
  "Return `t' if we have gpg public keys for all recipients of this message=
."
  (require 'epa-mail)
  (if (and (not (message-news-p))  ; No encryption for news,=20
           (or (message-fetch-field "to") (message-fetch-field "cc"))) ; we=
 have to have one address at least
      (catch :exit
        (mapc
         (lambda (addr)
           ;; check for a usable key - taken from epa-mail.el
           (if (not (epa-mail--find-usable-key
                     (epg-list-keys
                      (epg-make-context epa-protocol)
                      (downcase (mail-strip-quoted-names addr)))
                     'encrypt))
               (throw :exit nil)))
         (message-tokenize-header (concat
                                   (message-fetch-field "to")
                                   ","
                                   (message-fetch-field "cc"))))
        t)
    nil))

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Opportunistic encryption, here we go.

a.

=2D-=20
Evil exists to glorify the good. Evil is negative good.
It is a relative term. Evil can be transmuted into good.
What is evil to one at one time,
becomes good at another time to somebody else.
                        - Sivananda

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