The Grapevine Project

steve jenson stevej@sieve.net
Wed, 05 Dec 2001 17:43:56 -0800


Stephen Blackheath wrote:
 >

> On Thu, 06 Dec 2001 13:00, you wrote:
> 
>>Stephen Blackheath wrote:
>>
>>>We use a 'hash cash' technique
>>>(which we call "Solve A Hard Problem") for defence against
>>>denial-of-service attacks - the assumption being that legitimate nodes
>>>have more CPU power than attackers.
>>>
>>that seems like a silly assumption. What about DDoS?
>>
> 
> Firstly, understand that when I say "legitimate nodes have more CPU power", I 
> am referring to the sum of all legitimate nodes vs. the sum of all attackers.


So it's not so much an assumption as a constraint? I'm not trying to be 
nitpicky but to clear up ambiguity. Speaking of constraints, I'm unable
to find a clear, concise Threat Model established in your literature.


> Ultimately, if an attacker has more of something than you do, then the 
> attacker will win.  The only thing you have control over as designer is what 
> that something is.  We chose CPU time rather than network bandwidth or access 
> to IP addresses, because none of the strategies relating to the latter things 
> seemed to work.  I am certainly open to better ideas.


This isn't necessarily true, have you read Ross Anderson's excellent
work 'Security Engineering' (ISBN 0471389226)? He outlays possible
strategies to protect agains *DoS, one of which is late binding of
names.

 
> DDoS - if you're talking about it as an attack from nodes outside the network 
> - - is difficult against the Grapevine due to the high cost of 'harvesting' IP 
> addresses.


No, I'm talking about malicious nodes from within your network working 
in tandem.

cheers,

steve