Re: Problems with implementation - DoS attacks possible

Hello.

[cut]

> These means the disclosure key of previous TRACEBACK messages
>   will be included in next TRACEBACK message.
>
> So, if the comming DoS traffic is as forged ICMP traceback,  under the
> jammy noisy traffic, the collector need to "*WAIT" the disclosure key.

Exactly.


> But, if the disclosure key comes first or same-time don't you think it
> becomes better?

Hash algorithm is a one-way function. If the key is disclosured, everyone
can spoof a ICMP Traceback message.
Very simple explanation:
P(_message_ + _key_material_) = _hash_

In itrace we know only P() function, _message_ and _hash_. So, we can't
check if the _hash_ is correct as far as we don't have _key_material_. If
the router will disclosure his _key_material_, we will be able to make the
same P() function as router did before and check if the hash is correct.
Moreover, we can now produce our own hash for our spoofed message:
P(_spoofed_message_ + _key_material_) = _spoofed_hash_
So, you can see now, that after key disclosure we musn't use that key
anymore.

We are not talking about digital signatures here! We are hashing only and
nothing more. The digital signature will be used only in Key Disclosure
List element.

The main reason for such solution is speed. Hash algorithms are very
fast - we can use it on every ICMP Traceback packet. Digital signatures
are much slower - we will use it only to sign Key Disclosure List which
means we need to do this only when keys are changing.



> >Assuming I have 622 Mbps speed and I'm flooded with ICMP Traceback
> >messages. The time beetwen key change is one hour. Imagine how big
> >buffer-1 must be...
> >
>
> If the full network speed were available, it is about 80MB/s. Assuming
> the average size of packets were 500 bytes, it is about 160,000 packet/s.
>
> If we use a PC of 1GB Memory as collector, the memory will be filled up
>   about 10 seconds, though we need to backup the data to HDD until then.

You need a big HDD to collect all messages :)
What I'm saying here it is *not possible* to collect all messages (and
yes, I'm connected 622 Mbps to the Internet and I recently experienced an
attack at >500 Mbps speed).


> > >    iii) Configure the lifetime of the key much longer
> >
> >I rather hoped it will be much shorter :)
>
> I think this issue comes from or depends on the weakness of Hash or PKI tech,
> and traceback is not necessary success, so I think the lifetime, actually days
>   or week level, can be acceptable. I hope so but not nesessary.

Untrue.


---
Tomasz Grabowski  (0-91)4494234
Akademickie Centrum Informatyki
mailto:[email protected]