On 01/30/2012 11:33 PM, Michael Hendricks wrote: > On Mon, Jan 30, 2012 at 7:05 PM, Gavin Andresen <gavinandre...@gmail.com> > wrote: >> Given the randomness in Pieter's design, that seems extremely unlikely >> / difficult to do. Is it possible to do a back-of-the-envelope >> calculation to figure out what percentage of nodes on the network an >> attacker would have to control to have a (say) 1% chance of a >> successful Sybil attack? > The randomness prevents finely crafted attacks since an attacker can't > predict which bucket his address ends up in. I don't think it helps > against brute force attacks though. If 60% of the network's nodes are > controlled by an evil botnet, 60% of the nodes we pull out of the > address manager point to the attacker. If a client has 8 connections > to the network, a Sybil attack would succeed 1.7% of the time. At > current network size, 60% of listening nodes is 2,800; only 2-5% of a > decent botnet. > > Nodes that accept incoming connections are far less vulnerable, since > the probability of success decreases exponentially with the number of > connections. 95% botnet control with 125 connections has 10^-6 chance > of success. > > Perhaps we could add a command-line option for increasing the maximum > number of outbound connections. That way, nodes unable to accept > incoming connections can easily decrease their susceptibility to Sybil > attack. > >> I've also been wondering if it is time to remove the IRC bootstrapping >> mechanism; it would remove a fair bit of code and we'd stop getting >> reports that various ISPs tag bitcoin as malware. When testing the >> list of built-in bootstrapping IP addresses I always connect fairly >> quickly, and the DNS seeding hosts seems to be working nicely, too. > I think it should be disabled by default one release after the new > address manager is released. That way, we're not changing too many > parts of the bootstrapping process at once. > > As an aside, I can't help but wonder whether ISPs blocking IRC traffic > filters some botnets out of the IRC bootstrapping channels; keeping > them more "pure". > If the number of outbound connections is increased the delay of transaction broadcast code needs to be improved to avoid a broadcast storm.
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