[lwip-users] Re: [lwip] TCP sequence number attacks

[Adam Dunkels]

On Fri, 2002-08-16 at 22:56, Paul Sheer wrote:
> > The right way to solve it isn't just to do iss = random(), though. I
> 
> it is with PaulOS, because PaulOS random() is secure

The problem isn't with the randomness, but with the probability for
hitting "old" sequence numbers that have been used recently. Here is
what RFC1948 says:

   The choice of initial sequence numbers for a connection is not
   random.  Rather, it must be chosen so as to minimize the probability
   of old stale packets being accepted by new incarnations of the same
   connection [6, Appendix A].  Furthermore, implementations of TCP
   derived from 4.2BSD contain special code to deal with such
   reincarnations when the server end of the original connection is
   still in TIMEWAIT state [7, pp. 945].  Accordingly, simple
   randomization, as suggested in [8], will not work well.

/adam
-- 
Adam Dunkels <address@hidden>
http://www.dunkels.com/adam/

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