On Wed, 2003-08-20 at 09:16, Steve Crook wrote: [..] > When Minion is launched, it will be difficult to estimate the rate at > which nodes/pingers/directory servers will join. Based on this, is it > not possible that a resourceful attacker could introduce services which > would enable him to control the quorum? [Steve and I discussed this on IRC, but I'm writing to the list too for the record.] There aren't supposed to be an arbitrarily large amount of voting directory servers. If there were, we'd have exactly the same problem of knowing which directory servers to trust that we do with knowing which mixes to trust. Instead, the default quorum should contain a handful of directory servers (say, between 5 and 9). All of these should be run by well known people and organizations, living and operating in different jurisdictions. An attacker can alway sign up more directory servers ... but unless the attacker can get the members of a good quorum to trust the attacker's servers, those servers can not join the quorum. (It's okay if the attacker has his own quorum of 25 servers floating off in the middle of nowhere... users who decide to use that quorum instead are screwed, but in this case, we can't save users from their own bad judgment.) If the attacker persuades _some_ of the servers in the good quorum to trust *enough* of the attackers' servers, the attacker may be able to lure those "confused" servers into preferring the attacker's quorum. (For instance, suppose the default quorum has good servers G1...G6, along with confused servers C1,C2,C3. Suppose the attacker signs up M1...M7. If the attacker persuades C1...C3 to trust M1...M7, and M1...M7 are listed as trusting C1...C3 and themselves, then the attacker's larger quorum will pull <C1...C3,M1...M7> into a separate quorum, leaving G1...G6 on their own.) (Of course, in this case, the attacker still cannot produce a directory signed by more than half of the default quorum, unless the attacker manages to confuse at least half of the default quorum in this way.) HTH, -- Nick
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