| Re: the last link >In the Kademlia adaption for Bittorrent a peer's address (NodeID) is to be generated randomly, or more appropriate: arbitrarily. Because randomness isn't verifiable, an implementation can advertise itself with popular NodeIDs or even change them on a per-packet basis. At the end of the slides they suggest sha1(ip+port) as a possible fix. This would increase the barrier-to-entry of a Sybil attack to the point where an attacker needs to be able to spoof IP addresses or connections. However, I believe that a sufficiently motivated and financially equipped attacker may already exist who would still be able to attack this scheme. Perhaps an alternative to sha1(ip+port) could be some form of cryptographic signature scheme, where the NodeID is a public key or hash of a public key, and a node is only considered "real" if it is at least able to sign responses with the private key that corresponds with the NodeID. Maybe operators of nodes should be allowed to tweak some kind of setting that controls how paranoid the node should be of Sybil attacks. Maybe it would be possible to include some kind of hashcash or Bitcoin scheme to make Sybil attacks more costly. There has to be some way of requiring an attacker to expend considerable computation power. |