Re: depleting the random number generator

[David Honig]

At 04:45 PM 7/17/99 -0400, John Denker wrote:
>Hi Folks --
>
>I have a question about various scenarios for an attack against IPsec by way 
>of the random number generator.  The people on the linux-ipsec mailing list 
>suggested I bring it up here.

>>..worries that /dev/random exhaustion -> DoS, and /dev/urandom -> PRNG after
exhaustion..

You are correct.  There is no way around this, except to add a true RNG
to your server.  With an open source OS, you can add this to the existing
/dev/[u]random code

Commercial devices range from serial-port dongles to expensive crypto
accelerator
cards that include RNGs.  

If you are willing to build and test your own equiptment, you can use 
FM hiss, radiation, or electronic noise as a source of physical entropy.
You will have to condition the bits; see RFC 1750.

In both cases you'll have to hack your /dev/random code to integrate it
transparently.  But it is unavoidable if you want to do your security
properly.