Re: [tcpm] Q&C regarding tcpsecure-09 recommendations

[Joe Touch <[e-mail]>]

Anantha Ramaiah (ananth) wrote:
...
>> 	- with source port randomization, the mitigations are not needed
>> 	(port randomization provides a 2^15 strength amplification),
>> 	even presuming source IP addresses are known
> 
> Source port randomization is one way of adding robustness and does not
> every situation. Also you can't assume everyone is doing src port
> randomization. 

No, you cannot. The responsibility for protecting the session then falls 
to the side that initiates it (fair territory, IMO), rather than the 
side that receives the RST (which is arbitrary).

> Even then having these mitigations would make the attacks
> described in the document harder to accomplish.

Agreed that it makes the attacks still harder, but if they're already 
hard enough, then the mitigations aren't needed.

>> 	- if source IP addresses are not known, the mitigations are not
>> 	needed
> 
> I think this is very obvious in the document. Right from the intro which
> talks about the attack vectors, and what is needed to accomplish the
> attack. 
> 
>> 	- the mitigations may increase the time needed to respond to
>> 	a legitimate RST, incurring extra RTTs or retransmissions
>> 	vs. an unmodified system
> 
> Yes, this is obvious too due to the challenge ACK being sent.
> 
>> 	- the mitigations are not a substitute for network or
>> 	transport authentication, either of which obviate the need
>> 	for the mitigations (yes, this is noted in the security
>> 	considerations, but it's buried w.r.t. applicability)
> 
> Oh, the way I read the draft the above fact is mentioned all over the
> draft.. I can point out all the places if you want, but we have been
> thru this before and I have incorporated the feedback received from you
> but I am surprised that you are bringing this one up now.

I noted below why I am raising it now (the FreeBSD note).

>>   - the mitigations protect only off-path attacks; on-path
>> 	attacks, such as ISPs shutting connections down deliberately,
>> 	are not prevented by this mitigation (yes, also noted
>> 	in security considerations, but again worth noting in
>> 	applicability, and worth adding the ISP example, IMO)
> 
> Well, I would think that we generally don't want to repeat the same text
> all over the document again and again, but if the work group believes in
> this redundancy as you semm to do, I am more than willing to add it. 

I don't think it's huge; it is just a summary of - as you note - 
information noted elsewhere.

Joe

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