Subject: Re: [Bitcoin-development] Peer Discovery and Overlay

From: Peter Todd <[email-masked]>
Date: Tue, 24 Dec 2013 09:02:28 -0500

On Tue, Dec 24, 2013 at 12:52:46AM -0800, Jeremy Spilman wrote:
> Some really nice efforts out there to map and analyze the bitcoin P2P  
> network.
> 
> The current protocol apparently recommends returning up to 2500 addresses  
>  from 'getaddr'. I'm not sure how much clients are expected to probe the  
> address space in order to select 'far-apart' peers, or how much such an  
> process would even attempt to achieve.

The logic is that by simply connecting to peers at random you keep the
network structure as a whole randomized. You don't need to make any
specific attempt at connecting to "far-apart" peers.

> How much does it matter if the ability to discover the entire network of  
> peers is fast or slow? There are probably pros and cons to both.
> 
> Is there any thought to how existing bitcoin node relations, and the ease  
> at which peers can be discovered, becomes a service in itself, or even  
> possibly a vulnerability?

Keep in mind it's easy for better knowledge of the network to be a
vulnerability; the number of full nodes is small enough that DoS
attacking all of them is quite feasible.

The other big vulnerability is that getaddr data is best effort; we
currently have no mechanism to ensure that nodes are in fact operated by
separate individuals. It'd be quite easy for someone to set up a
relatively small number of nodes that only advertise themselves in the
getaddr information. Over time they would get proportionally more
incoming connections than is "fair"

As for node addresses being a service, that's what the DNS seeds are!
bitcoinj clients, for instance, depend very heavily on those seeds and
can be easily compromised in a variety of ways by them.

-- 
'peter'[:-1]@petertodd.org
000000000000000092a315c01cfc115d7f1b40dc44edbafd504b0d7498b0704a