Re: [Bitcoin-development] Protocol extensions

[Christian Decker <decker.christian@gmail.com>]

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For the future evolution without considering DHTs:
While I think we will sooner or later have supernodes, I don't think they
will need to be trusted too much.
Supernodes will be those nodes that verify all transactions and make them
available to miners. Since miners will become more and more specialized
these supernodes are likely to be owned by the miners themself. To be a
miner either you need to verify all the transactions you include (otherwise
others might be able to find an error in your block and thus drop it) or
have someone that verifies them for you. In the end I think we'll end up
with a hierarchical network, with the miners/supernodes tighly
interconnected at the top and the lightweight clients that simply verify
transactions (or their inputs to be precise) that are destined for them at
the bottom.

As for the DHT we had a few brainstorming sessions a while back on the
forum http://bit.ly/sc2RLZ (gmaxwell didn't like it then either :D)
Forcing someone to participate in a fixed position in the block storage
network is a good way to reduce the risk of a sybil attack as Michael said.
The hash should include only information that cannot be changed by the
user, so IP can be used, but including the port is risky.

Broadcasting the transactions would not need to be done, since miners fetch
them from their storage place, alternatively we could use the inv broadcast
to notify peers about a new block/transaction and let it retrieve them from
the permanent storage (DHT or block storage network). If we route traffic
internally in the DHT we could even start caching at nodes leading to the
real location, since announcements would lead to flashcrowds, putting heavy
load on the responsible nodes. Caching is not a risk since the hash of the
object to be retrieved is already known.

Regards,
Chris

On Wed, Dec 21, 2011 at 1:41 PM, Michael Grønager <gronager@ceptacle.com>wrote:

> I find it likely that we will at some point have supernodes. If we have
> browser based wallets then the server for these automatically becomes
> supernodes. Further, if we move along that direction, it becomes much
> simpler to use both the scheme I proposed or to use a a lot of other
> schemes for sharing the validation work on a farm constituting the
> supernode.
>
> However, if we want to keep bitcoin in a real p2p setup and enable
> scalability in terms of ensuring both thin and fat client to connect then
> we need to go along the path I propose.
>
> Actually, after thinking a bit more about the possible new attack vector I
> don't find it that alarming - if you still require 7 confirmations of any
> bigger transaction before you, as receiver accepts the transaction as payed
> you will not risk anything. The question is then if it is sufficiently easy
> to fake small transaction to e.g. gain access to micropayment based web
> services. I would again say no - the requirement that you have ok from e.g.
> 8 different A.B nodes will make it extremely difficult to cheat, and that
> would even require you to gain some level of control over the network that
> the service you want to cheat is connected through.
>
> This means that you should not divide the hash space more finely than you
> would at all times be able to find 8 different A.B nodes. As the number of
> clients grows you can then divide the hash space further. (with 100000
> nodes today and a division into 512 parts you would have approx 200 nodes
> to choose from).
>
> Cheers,
>
> M
>
>
>
> On 21/12/2011, at 12:42, Eric Lombrozo wrote:
>
> > Is it just me or does it seem inevitable that at some point supernodes
> > will emerge that other nodes trust to validate transactions for them?
> > Supernodes needn't even store the entire block chain and transaction
> > pool...it would be sufficient that they keep lists of IP addresses of
> > other trustworthy nodes and partition them into a hashspace.
> >
> > Anonymous peers have no reputation to defend...but a trusted supernode
> > would, which could provide just enough incentive for the supernode to
> > do its best to ensure the nodes it vouches for are indeed legit. Of
> > course, unless the supernode is validating the entire block chain and
> > transaction pool itself, it could only assess the trustworthiness of
> > other nodes by performing random sampling.
> >
> > Michael, I really like your ideas and the clarity you bring to the
> > issue. Regarding the potential attack vector you mention, would it be
> > possible to partition the hashspace to minimize the risk that an
> > attacker can manage to disproportionately gain control over a part of
> > the hashspace?
> >
> >
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