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From: Jesper Harder <harder@myrealbox.com>
Subject: Re: UUIDGEN in lisp
Date: Sun, 15 Feb 2004 01:27:31 +0100	[thread overview]
Message-ID: <m3smhdmbkc.fsf@defun.localdomain> (raw)
In-Reply-To: mailman.2398.1076783242.928.help-gnu-emacs@gnu.org

Brad Collins <brad@studiojungle.net> writes:

> But I really do need to use a proper UUID.
>
> I've been trying to see how it's been done by others but it's not
> easy stuff.  I still don't understand about high and low parts of a
> time stamp and how to convert them..

Well, the time-based UUID is annoying to generate -- it requires
system-wide storage of a seed.  I don't see how you can guarantee
that your generator will use the same storage as, say, the Perl
generator and whatever else might generate UUIDs on ms-windows.

This type of UUID also leaks your MAC address.

Random-based UUIDs are much nicer.  Below is an implementation.  It
uses /dev/urandom as a source of high quality random bits on
GNU/Linux, but I don't know if the built-in `random' in Emacs used on
other systems qualifies as a "cryptographic strength random number
generator".

(defun uuid ()
  "Generate a version 4 UUID."
  (let ((bytes (uuid-random)))
    (setf (nth 7 bytes)
	  (logior #B01000000 (logand #B01111111 (nth 7 bytes))))
    (setf (nth 8 bytes)
	  (logior #B01000000 (logand #B01001111 (nth 8 bytes))))
    (apply 'format
	   "%02x%02x%02x%02x-%02x%02x-%02x%02x-%02x%02x-%02x%02x%02x%02x%02x%02x"
	   bytes)))

(defun uuid-random ()
  "Return a list of 16 random bytes."
  (if (file-readable-p "/dev/urandom")
      (let (((coding-system-for-read 'binary)))
	(mapcar 'identity
		(substring
		 (string-as-unibyte
		  (shell-command-to-string
		   "dd count=16 bs=1 < /dev/urandom"))
		 0 16)))
    (random t)
    (mapcar 'random (make-list 16 255))))

  parent reply	other threads:[~2004-02-15  0:27 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <mailman.2374.1076727586.928.help-gnu-emacs@gnu.org>
2004-02-14  4:05 ` UUIDGEN in lisp Jesper Harder
2004-02-14 18:23   ` Brad Collins
     [not found]   ` <mailman.2398.1076783242.928.help-gnu-emacs@gnu.org>
2004-02-15  0:27     ` Jesper Harder [this message]
2004-02-15  4:16       ` Brad Collins
2004-02-15 16:05         ` Brad Collins
     [not found]       ` <mailman.2412.1076818749.928.help-gnu-emacs@gnu.org>
2004-02-15 20:47         ` Jesper Harder
2004-02-16 10:04           ` Eli Zaretskii
2004-02-16 13:47           ` Brad Collins
     [not found]           ` <mailman.2461.1076925909.928.help-gnu-emacs@gnu.org>
2004-02-16 16:30             ` Jesper Harder
2004-02-16 19:48               ` Eli Zaretskii
     [not found]               ` <mailman.2509.1076960950.928.help-gnu-emacs@gnu.org>
2004-02-16 21:05                 ` Jesper Harder
2004-02-17  6:46                   ` Eli Zaretskii
     [not found]                   ` <mailman.2546.1077000306.928.help-gnu-emacs@gnu.org>
2004-02-17 18:45                     ` Jesper Harder
2004-02-17 20:08                       ` Eli Zaretskii
     [not found]                       ` <mailman.2586.1077048551.928.help-gnu-emacs@gnu.org>
2004-02-17 21:21                         ` Jesper Harder
2004-02-18  6:34                           ` Eli Zaretskii
2004-02-19 16:57                         ` Stefan Monnier
     [not found]           ` <mailman.2471.1076940207.928.help-gnu-emacs@gnu.org>
2004-02-16 17:10             ` Jesper Harder
2004-02-14 18:54 ` Kai Grossjohann
2004-02-15  2:37   ` Felix
2004-02-14  2:57 Brad Collins

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