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Re: Random Sequence Numbers
From: smb () RESEARCH ATT COM (Steven M. Bellovin)
Date: Thu, 10 Feb 2000 17:35:03 -0500


In message <00Feb10.090608est.115219 () border alcanet com au>, Peter Jeremy write
s:
On 2000-Feb-09 20:27:08 +1100, Omachonu Ogali <oogali () intranova net> wrote:
I don't know if anyone else attempted, but I whipped up a little patch for
FreeBSD that randomizes the sequence/acknowledgment numbers sent by TCP
instead of incrementing it by one each time. Apply using 'patch'.

Note that the patch is using libkern/random().  This function is a
simple, multiplicative PNRG with 32-bits of state (all of which is
`leaked' via its return value.  Whilst the change might be better than
a simple increment/decrement, I don't believe it provides any real
security (especially in view of the %=2 operations).

I never saw the original posting to this; let me suggest that folks read RFC
1948 before doing sequence number randomization.

                --Steve Bellovin


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