Re: [PROPOSAL/PATCH] Fortuna PRNG in /dev/random

Jean-Luc Cooke
2004-09-27T15:21:07Z

Thanks.

My re-writing wilol appear as more like an editorial revision than a
re-write.

I will certainly talk to Jamal et al. Thanks

JLC

On Mon, Sep 27, 2004 at 10:55:55AM -0400, Theodore Ts'o wrote:
> On Mon, Sep 27, 2004 at 09:32:03AM -0400, Jean-Luc Cooke wrote:
> >
> > I'll read over this once I finish re-writing my patch to use your entropy
> > estimation.
>
> While you're at it, please re-read RFC 793 and RFC 1185. You still
> don't have TCP sequence generation done right. The global counter
> is being increased for every TCP connection, and with only eight bits,
> it can wrap very frequently. Encrypting the source/destination
> address/port tuple and using that as an offset to the global clock,
> and then only bumping the counter when you rekey would be much more in
> the spirit of RFC 1185, and would result in sequence numbers much less
> likely to cause stale packets to get mistakenly accepted.
>
> I'm still a bit concerned about whether doing AES is going to be a
> speed issue. Your comparisons against MD4 using openssl don't really
> prove much, because (a) the original code used a cut-down MD4, and (b)
> the openssl benchmark does a large number of encryptions and nothing
> else, so all of the AES key schedule and tables will be in cache.
>
> The only real way to settle this would be to ask Jamal and some of the
> other networking hackers to repeat their benchmarks and see if the AES
> encryption for every TCP SYN is a problem or not. CPU's have gotten
> faster (but then again so have networks, and memory has *not* gotten
> much faster), so only a real benchmark will tell us for sure.
>
> - Ted