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[Emacs-diffs] master a757149 1/2: Identify unsafe combinations of Bcc an
From: |
Lars Ingebrigtsen |
Subject: |
[Emacs-diffs] master a757149 1/2: Identify unsafe combinations of Bcc and encryption |
Date: |
Sun, 27 Dec 2015 18:25:38 +0000 |
branch: master
commit a757149ca49c1ae0b70ef74c2181e0fb10a81f5e
Author: Jens Lechtenboerger <address@hidden>
Commit: Lars Ingebrigtsen <address@hidden>
Identify unsafe combinations of Bcc and encryption
* lisp/gnus/gnus-util.el (gnus-subsetp): New function
* lisp/gnus/mml-sec.el (mml-secure-safe-bcc-list): New variable
* lisp/gnus/mml-sec.el (mml-secure-bcc-is-safe): New function
---
lisp/gnus/gnus-util.el | 10 ++++++++++
lisp/gnus/mml-sec.el | 46 ++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 56 insertions(+), 0 deletions(-)
diff --git a/lisp/gnus/gnus-util.el b/lisp/gnus/gnus-util.el
index 40e2dcf..933387d 100644
--- a/lisp/gnus/gnus-util.el
+++ b/lisp/gnus/gnus-util.el
@@ -1989,6 +1989,16 @@ to case differences."
(defun gnus-timer--function (timer)
(elt timer 5)))
+(defun gnus-subsetp (list1 list2)
+ "Return t if LIST1 is a subset of LIST2.
+Similar to `subsetp' but use member for element test so that this works for
+lists of strings."
+ (when (and (listp list1) (listp list2))
+ (if list1
+ (and (member (car list1) list2)
+ (gnus-subsetp (cdr list1) list2))
+ t)))
+
(provide 'gnus-util)
;;; gnus-util.el ends here
diff --git a/lisp/gnus/mml-sec.el b/lisp/gnus/mml-sec.el
index 45da937..dbae280 100644
--- a/lisp/gnus/mml-sec.el
+++ b/lisp/gnus/mml-sec.el
@@ -122,6 +122,21 @@ Whether the passphrase is cached at all is controlled by
:group 'message
:type 'integer)
+(defcustom mml-secure-safe-bcc-list nil
+ "List of e-mail addresses that are safe to use in Bcc headers.
+EasyPG encrypts e-mails to Bcc addresses, and the encrypted e-mail
+by default identifies the used encryption keys, giving away the
+Bcc'ed identities. Clearly, this contradicts the original goal of
+*blind* copies.
+For an academic paper explaining the problem, see URL
+`http://crypto.stanford.edu/portia/papers/bb-bcc.pdf'.
+Use this variable to specify e-mail addresses whose owners do not
+mind if they are identifiable as recipients. This may be useful if
+you use Bcc headers to encrypt e-mails to yourself."
+ :version "25.1"
+ :group 'message
+ :type '(repeat string))
+
;;; Configuration/helper functions
(defun mml-signencrypt-style (method &optional style)
@@ -272,6 +287,37 @@ Use METHOD if given. Else use `mml-secure-method' or
(interactive)
(mml-secure-part "smime"))
+(defun mml-secure-is-encrypted-p ()
+ "Check whether secure encrypt tag is present."
+ (save-excursion
+ (goto-char (point-min))
+ (re-search-forward
+ (concat "^" (regexp-quote mail-header-separator) "\n"
+ "<#secure[^>]+encrypt")
+ nil t)))
+
+(defun mml-secure-bcc-is-safe ()
+ "Check whether usage of Bcc is safe (or absent).
+Bcc usage is safe in two cases: first, if the current message does
+not contain an MML secure encrypt tag;
+second, if the Bcc addresses are a subset of `mml-secure-safe-bcc-list'.
+In all other cases, ask the user whether Bcc usage is safe.
+Raise error if user answers no.
+Note that this function does not produce a meaningful return value:
+either an error is raised or not."
+ (when (mml-secure-is-encrypted-p)
+ (let ((bcc (mail-strip-quoted-names (message-fetch-field "bcc"))))
+ (when bcc
+ ;; Split recipients at "," boundary, omit empty strings (t),
+ ;; and strip whitespace.
+ (let ((bcc-list (split-string hdr "," t "\\s-+")))
+ (unless (gnus-subsetp bcc-list mml-secure-safe-bcc-list)
+ (unless (yes-or-no-p "Message for encryption contains Bcc header.\
+ This may give away all Bcc'ed identities to all recipients.\
+ Are you sure that this is safe?\
+ (Customize `mml-secure-safe-bcc-list' to avoid this warning.) ")
+ (error "Aborted"))))))))
+
;; defuns that add the proper <#secure ...> tag to the top of the message body
(defun mml-secure-message (method &optional modesym)
(let ((mode (prin1-to-string modesym))