On 04/27/2014 05:36 AM, Sergio Lerner wrote: >> Without invoking moon math or assumptions of honest peers and >> jamming-free networks, the only way to know a chain is valid is to >> witness the each and every block. SPV nodes on the other hand, >> simply trust that the most-work chain is a valid chain, based on >> economic arguments about the opportunity cost of mining invalid >> blocks. > I argue that you cannot talk about "the most-work chain" without > actually making an assumption about honest peers.
I should have said "without invoking moon math or interactive protocols requiring honest peers over jamming-free networks." The interactive protocol was more the point than the honest peers and jamming-free network. Yes, without an honest peer and an un-jammed network, you might never learn about the most-work chain in the first place. But having the security of the proof not depend on query access to an honest full node is absolutely necessary for some applications and certainly desirable in others. Although strictly speaking what I said may not be 100% true. The single alternative solution I've seen involves some sort of Fiat–Shamir transform that could give you a probabilistic proof by including random additional paths through the block chain chosen based on the combined hash of the headers. However this is disadvantageous as it massively increases the proof size and verification time, and you have to include a lot of data to achieve assurance that more work was required to generate the fraud than an honest chain. > If you do not make the assumption, you compute the "economic > arguments" wrong. Not necessarily. By requiring connectivity you know that what you are receiving is built off of the main chain, for example, and you can still make assumptions about resulting opportunity costs. > First this is a method that uses NPPs, not SPV proofs. Since the > method chooses all peers that are synchronized (have the latest > current block) then going back means only skipping a potential short > fork (which I suppose has never been more than 3 blocks during normal > network conditions). You're looking for a common ancestor, not the > checkpoint. So the linear scan is actually O(1). The exact value can > be approximated by the sum of the convergent infinite geometrical > sequence of forking probabilities, which it's about 1.03 without > considering selfish-mining, and probably less than 2.03 considering > it. Unless you're connected to attacker nodes which are wildly divergent from each other. It's relatively easy to create a massive fake history of difficulty-1 blocks. If you assume honest peers things get very easy. But that's not a safe assumption to be making. With back-link block-history commitments, on the other hand, an interactive protocol allows you to do a binary search to find common ancestors, and have trust that the intermediate links actually exist. ------------------------------------------------------------------------------ Start Your Social Network Today - Download eXo Platform Build your Enterprise Intranet with eXo Platform Software Java Based Open Source Intranet - Social, Extensible, Cloud Ready Get Started Now And Turn Your Intranet Into A Collaboration Platform http://p.sf.net/sfu/ExoPlatform _______________________________________________ Bitcoin-development mailing list Bitcoinfirstname.lastname@example.org https://lists.sourceforge.net/lists/listinfo/bitcoin-development