[Openswan Users] /dev/random question

[Paul Wouters]

On Wed, 23 Nov 2005, Nick wrote:

> I tried doing the "ipsec newhostkey" on a machine of mine, and after 30+
> minutes it still wasn't finished.
>
> So I told it to use /dev/urandom instead of /dev/random, and it was
> finished in a few seconds.

Yes, but you should not do that, since the /dev/urandom random is not
as strong as the /dev/random.

> From what I understand /dev/random can take an extremely long time if it
> is a headless box with no hard drive (just a small flash card), which is
> all you really need for a VPN router.

One way to bypass this is to generate the host key on another machine.

> Anyway I am wondering if this is going to cause a problem with the normal
> operation of openswan.  I don't know if it uses /dev/random in normal
> operation, other than generating keys/certs.

No, for all other uses, /dev/urandom is used, since it is strong enough for
session keys that last an hour. Your RSA key that you generate with the
newhostkey command though might be active for years, and should not be using
a weaker form of random. If hardware random support is detected, that is
used instead. (eg when using a VIA C3 with PadLock)

> I really would like to use /dev/random, but it's not just a problem of
> waiting (possibly several hours) once.  This is actually a little distro
> that I use for a fair amount of people/customers so I can't effectively
> have them all wait some extremely long (and unknown) time for the
> keys/certs to generate.  I wish there was a way to speed this up without
> using /dev/urandom, but I don't know how.  It looks like the new intel
> motherboards (which is what we are using, all new p4/celeron based
> systems) don't have the onboard random number generator.  And I don't want
> to buy a hardware card just for this.

Give your customers the box with a pre-calculated key, or write some application
that they can run on their machine to generate the key and upload to your
appliance.

Paul