[Mono-list] For those interested in the Guid class.

Brian Jepson bjepson@oreilly.com
Wed, 19 Sep 2001 22:06:26 -0400 (EDT)

On 19 Sep 2001, Miguel de Icaza wrote:

> So it seems like the decent thing to do these days is to use random
> data instead of using a computer Mac address (which raises some
> privacy issues).

e2fsprogs (http://e2fsprogs.sourceforge.net/) comes with libuuid.so.  It
exports some functions for generating uuids.  If you have e2fsprogs-devel
installed, you should be able to find some info in
/usr/include/uuid/uuid.h.  Even if you can't use the library directly,
perhaps the algorithm will be of help.

On my system, the manpages weren't installed by default, but here is what
I found in the source distro's uuid_generate.3 file:

    The  uuid_generate  function  creates  a  new  universally
    unique  identifier  (UUID).   The  uuid  will be generated
    based on high-quality  randomness  from  /dev/urandom,  if
    available.   If  it  is  not available, then uuid_generate
    will use an alternative algorithm which uses  the  current
    time,  the  local ethernet MAC address (if available), and
    random data generated using a pseudo-random generator.

    The uuid_generate_random function forces the  use  of  the
    all-random UUID format, even if a high-quality random num-
    ber generator (i.e., /dev/urandom) is  not  available,  in
    which  case  a pseudo-random generator will be subsituted.
    Note that the use of a pseudo-random generator may compro
    mise the uniqueness of UUID's generated in this fashion.

    The  uuid_generate_time  function  forces  the  use of the
    alternative algorithm which uses the current time and  the
    local ethernet MAC address (if available).  This algorithm
    used to be the default one  used  to  generate  UUID,  but
    because  of  the  use  of the ethernet MAC address, it can
    leak information about when and where the UUID was  gener-
    ated.   This  can  cause privacy problems in some applica-
    tions, so the uuid_generate function only uses this  algo-
    rithm if a high-quality source of randomness is not avail-

    The UUID is 16 bytes (128 bits) long, which gives approxi-
    mately  3.4x10^38  unique  values (there are approximately
    10^80 elemntary particles in  the  universe  according  to
    Carl Sagan's Cosmos).  The new UUID can reasonably be con-
    sidered unique among all UUIDs created on the  local  sys-
    tem,  and among UUIDs created on other systems in the past
    and in the future.

    The newly created UUID is returned in the memory  location
    pointed to by out.

    OSF DCE 1.1

Hope this helps,