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

[Ted Zlatanov <tzz@lifelogs.com>]

On Wed, 26 Nov 2008 03:43:56 +0900 Daiki Ueno <ueno@unixuser.org> wrote: 

>>>>>> In <867i6rd80c.fsf@lifelogs.com> 
>>>>>> Ted Zlatanov <tzz@lifelogs.com> wrote:
>> On Sat, 22 Nov 2008 07:45:16 +0800 anhnmncb <anhnmncb@sina.com> 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.

Ted

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 encryption."
+   :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)
  
  (eval-and-compile
    (if (fboundp 'encode-coding-string)
***************
*** 51,58 ****
  	   (eq key-id 'SYM))
        (progn
  	(setq file (file-truename file))
! 	(let ((entry (assoc file epa-file-passphrase-alist))
  	      passphrase)
  	  (or (copy-sequence (cdr entry))
  	      (progn
  		(unless entry
--- 57,81 ----
  	   (eq key-id 'SYM))
        (progn
  	(setq file (file-truename file))
! 	(let ((entry (assoc file epa-file-passphrase-alist))	      
  	      passphrase)
+ 	  ;; 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
+ 		     (< epa-file-cache-passphrase-for-symmetric-encryption-timeout
+ 			(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))
  	      (progn
  		(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))
  		passphrase))))
      (epa-passphrase-callback-function context key-id nil)))