These are real problems with both centralized and p2p networks. They can be more accessible with p2p networks because you *don't* have to create a global mitm -- you just have to poison Alice's list of peers. I think this is called an Eclipse attack (?)
But blockchain technologies are almost entirely focused on resolving this issue. 1. You cannot change the past unless you can duplicate the amount of work produced by the entire mining network up from the event in the past you want to change and the last point of sync as Alice. Only then can you produce a blockchain long enough to convince an already-sync'd client that yours is correct -- and what you have basically done at this point is create a new canonical blockchain that should and will be used by everybody, not just Alice. 2. Alice has a wide variety of options to circumnavigate a persistent MITM. She can use an overlay network such as Tor or I2P. She can share her blockchain with her friends using floppies. She can sync via ad-hoc wifi or send packets over amateur radio. She does not have these options if she is using a centralized system, where the MITM can surround the servers themselves. 3. Alice can check and see what is going on. When data is committed to a blockchain the data resides in a block which has a hash unique to that block and all parent blocks that came before it. If you are living in a fake blockchain, your transaction and block ids will mismatch those of the people you are interacting with. Your blockchain will have a much lower proof of work difficulty. A persistent MITM is technically possible, but you also have to MITM all the other channels of relevant data. If my friend is resolving an address differently than me, we simply have to exchange blocks to figure out what is going on and who is right. I'm not too experienced but the way people are talking seems to disregard the grey areas of these situations. Blockchains are incredibly good at storing globally unique, permanent information. They have classic P2P network issues. But once you can intercept all information exchanged by an individual with anybody, you can make them believe yellow is blue under any conditions. On 8/3/15, Jonathan Rudenberg <[email protected]> wrote: > >> On Jul 23, 2015, at 9:22 PM, Tao Effect <[email protected]> wrote: >> >> So, the only real option left is for a persistent, 24/7 global MITM. At >> that point you are no longer dealing with the Internet anymore. You might >> as well smash Alice’s computer with a brick and declare a successful >> “attack” on Namecoin. > > This is already known to exist, it is called QUANTUM INSERT[0]. Also, BGP > and DNS attacks can be used to accomplish the same thing. Let alone the > cheaper option of just hacking Alice’s WiFi. Throwing out MITM attacks as > not a viable threat is unreasonable at this point. > > Jonathan > > [0] https://en.wikipedia.org/wiki/Tailored_Access_Operations#QUANTUM_attacks > _______________________________________________ > Messaging mailing list > [email protected] > https://moderncrypto.org/mailman/listinfo/messaging > _______________________________________________ Messaging mailing list [email protected] https://moderncrypto.org/mailman/listinfo/messaging
