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Re: [feature request] epa-file-cache-passphrase-for-symmetric-encryption

From: Ted Zlatanov
Subject: Re: [feature request] epa-file-cache-passphrase-for-symmetric-encryption timeout.
Date: Tue, 25 Nov 2008 14:56:23 -0600
User-agent: Gnus/5.110011 (No Gnus v0.11) Emacs/23.0.60 (gnu/linux)

On Wed, 26 Nov 2008 03:43:56 +0900 Daiki Ueno <address@hidden> wrote: 

>>>>>> In <address@hidden> 
>>>>>> Ted Zlatanov <address@hidden> wrote:
>> On Sat, 22 Nov 2008 07:45:16 +0800 anhnmncb <address@hidden> wrote: 

a> symmetric file encryption is enough for me :)

>> ping...  If Daiki Ueno is not interested I can implement this, but I
>> wanted to give him a chance to do it since his coding style is pretty
>> different from mine.

DU> If you do want to implement this, you should consider:

DU> - At the moment I'd rather recommend users to use public-key encryption
DU> instead of symmetric encryption if they want passphrase caching, since
DU> they will benefit from gpg-agent which utilizes secure memory.  So it's
DU> intensional that epa-file handles symmetric case specially.  

I see.

DU> - As I said many times before (but you don't seem to understand),
DU> epa-file.el is an application and epg.el is a library.  

Thank you for explaining again.

My proposed patch follows.  I've tested it.


Index: epa-file.el
RCS file: /sources/emacs/emacs/lisp/epa-file.el,v
retrieving revision 1.14
diff -c -r1.14 epa-file.el
*** epa-file.el 30 Sep 2008 07:41:52 -0000      1.14
--- epa-file.el 25 Nov 2008 20:52:44 -0000
*** 29,40 ****
--- 29,46 ----
    :type 'boolean
    :group 'epa-file)
+ (defcustom epa-file-cache-passphrase-for-symmetric-encryption-timeout nil
+   "If non-nil seconds, time out the passphrase cache for symmetric 
+   :type 'integer
+   :group 'epa-file)
  (defcustom epa-file-select-keys nil
    "If non-nil, always asks user to select recipients."
    :type 'boolean
    :group 'epa-file)
  (defvar epa-file-passphrase-alist nil)
+ (defvar epa-file-passphrase-timeout-alist nil)
    (if (fboundp 'encode-coding-string)
*** 51,58 ****
           (eq key-id 'SYM))
        (setq file (file-truename file))
!       (let ((entry (assoc file epa-file-passphrase-alist))
          (or (copy-sequence (cdr entry))
                (unless entry
--- 57,81 ----
           (eq key-id 'SYM))
        (setq file (file-truename file))
!       (let ((entry (assoc file epa-file-passphrase-alist))          
+         ;; when we have an entry and we need to time out the passphrase,
+         ;; get the time of the passphrase entry for this file
+         ;; and if it's more than e-f-c-p-for-s-encryption-timeout seconds ago,
+         ;; set the entry's passphrase to nil so the user will have to re-enter
+         (when (and entry
+                    epa-file-cache-passphrase-for-symmetric-encryption-timeout)
+           (let ((timeout-entry 
+                  (car-safe 
+                   (cdr (assoc file epa-file-passphrase-timeout-alist)))))
+             (when (and
+                    timeout-entry
+                    (< 
+                       (time-to-seconds (time-since timeout-entry))))
+               (setq epa-file-passphrase-timeout-alist 
+                     (delete file epa-file-passphrase-timeout-alist))
+               (setcdr entry nil))))
          (or (copy-sequence (cdr entry))
                (unless entry
*** 63,68 ****
--- 86,94 ----
                (setq passphrase (epa-passphrase-callback-function context
                                                                   key-id nil))
                (setcdr entry (copy-sequence passphrase))
+               (setq epa-file-passphrase-timeout-alist
+                     (cons (list file (current-time))
+                           epa-file-passphrase-timeout-alist))
      (epa-passphrase-callback-function context key-id nil)))

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