Two KeyPair

Alphax alphasigmax at
Wed Nov 29 13:03:37 CET 2006

Henry Bremridge wrote:
> On Wed, Nov 29, 2006 at 08:20:06PM +1030, Alphax wrote:
>> That advice is seriously flawed. You do *not* want to copy the
>> random-seed file!
> Just out of interest: why?

As someone a lot smarter than me pointed out in a message I can't find
when I suggested "just copy the .gnupg directory" (and with a bit of
background info thrown in, and I'm not a cryptographer and haven't
really studied the GnuPG internals so I might be wrong):

GPG is a hybrid cryptosystem; messages are (symmetrically) encrypted to
"random" session keys, which are then (asymmetrically) encrypted to a
number of recipient public keys. Part of the security of the system is
that the session key is "random" or as close to it as possible; because
GPG will work on many different and varying systems, there is no
guarantee of a system-wide random data source, so you can't just read
from /dev/random or /dev/urandom every time you want a bit of random
data, because it might not exist (and these have their own problems).
So, GPG has it's own internal pseudorandom number generator. In order to
speed things up a bit, it normally has an internal seed of pooled random
data - which it stores in .gnupg/random_seed while it's not using it.
When GPG decides it wants some random data, it generates it using this
file as the seed - so if you know what the random seed file was, it's
(somewhat) easier to predict what the next lot of random data is going
to be. So, you don't want two installations of GPG to have the same
random_seed, because you're going to start producing deterministic output...

        Death to all fanatics!
  Down with categorical imperative!
OpenPGP key:

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