Re: [tcpm] Roman Danyliw's No Objection on draft-ietf-tcpm-rfc793bis-25: (with COMMENT)

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Date: Fri, 07 Jan 2022 21:13:11 -0800
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Subject: Re: [tcpm] Roman Danyliw's No Objection on draft-ietf-tcpm-rfc793bis-25: (with COMMENT)
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> On Jan 7, 2022, at 12:12 PM, Wesley Eddy <> wrote:
>> ** Section 3.4.  Per “There are security issues that result if an off-path
>> attacker is able to predict or guess ISN values”, a reference might be helpful
>> for this statement.  Perhaps [41] or [Morris185] from [41].
> ACK; Zahed also mentioned this and I think [41] is a good reference because it includes some more context beyond just [Morris1985] alone, and of course it includes reference to [Morris1985] itself as well.
The ISN is relevant only during the TWHS; otherwise, it’s not. I really wish we’d stop worrying so much about the ISN itself.

I.e., ISNs aren’t the issue; being able to guess or hit *inside the active window* is.

That can happen two ways - knowing the ISN *or* having the sequence numbers move through the whole number space.

And the latter is not mitigated by any sort of magically unpredictable ISN.