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Date:      Mon, 16 Apr 2001 13:08:14 -0700
From:      Kris Kennaway <kris@obsecurity.org>
To:        Darren Reed <avalon@coombs.anu.edu.au>
Cc:        Kris Kennaway <kris@obsecurity.org>, Mike Silbersack <silby@silby.com>, Mark T Roberts <newsletter@marktroberts.com>, freebsd-security@FreeBSD.ORG, net@FreeBSD.ORG
Subject:   Re: non-random IP IDs
Message-ID:  <20010416130814.A12057@xor.obsecurity.org>
In-Reply-To: <200104162002.GAA09062@caligula.anu.edu.au>; from avalon@coombs.anu.edu.au on Tue, Apr 17, 2001 at 06:02:42AM %2B1000
References:  <20010416120630.C10023@xor.obsecurity.org> <200104162002.GAA09062@caligula.anu.edu.au>

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On Tue, Apr 17, 2001 at 06:02:42AM +1000, Darren Reed wrote:

> > > You should optimize it for mod being 2^n-1 (or make that a requiremen=
t).
> >=20
> > I'm afraid I don't have time to look at this right now.  Perhaps it
> > can be revisited (the sysctl defaults to off for now), or Niels Provos
> > may be interested in the idea.
>=20
> Basically it means '% mod' -> '& mod' and call it with a 2^n-1 number.

Oh, okay.

> > Well, it still has wrapping properties like a network-order counter,
> > i.e. the algorithm attempts to order the output so that it doesn't
> > wrap within the segment lifetime.  That would be lost without using
> > HTONS.
>=20
> You're confusing properties of the local number and some opaque bits in
> a packet being sent over the 'net.

Quite likely.

Kris

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