Re: [briar-devel] Discovering Nodes etc.

[Michael R. <mi...@br...>]

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Hi g3ntleman,

The short answer to your question is Tor hidden services. Each device
publishes a Tor hidden service whenever it's online, which its
contacts can connect to regardless of the device's current IP address,
NAT, etc. Connecting through Tor conceals the social graph from
internet surveillance.

It's also possible for devices to connect directly to each other via
TCP, across the LAN or the internet. But connections across the
internet are unlikely to succeed for several reasons. First, as you
mentioned, contacts may not be online at the same time. Second, they
may not know each other's current IP addresses. Third, they may be
behind NATs or firewalls (very likely for mobile devices).

We have some measures to get around these problems: UPnP for automatic
port forwarding, and exchanging up-to-date IP addresses whenever
contacts can reach each other via any transport. But it's still
unlikely that two mobile devices will be able to reach each other
reliably via TCP. Worst of all, direct TCP connections reveal the
social graph to internet surveillance - and a peer discovery mechanism
such as a DHT would do the same. Because of all these issues, I've
disabled the internet TCP plugin in recent builds. The LAN TCP plugin
is still enabled.

In the long term we're planning two features that could help to
mitigate these issues. The first feature is called a repeater: a
device connected to wifi or Tor that acts as a dead drop for encrypted
data. Alice connects to the repeater and uploads a blob of encrypted
data for Bob, and later Bob connects to the repeater and downloads it.
Alice and Bob don't have to be in wifi range of each other, or online
at the same time, to communicate. The repeater can't read the data,
and if Alice and Bob connect to the repeater via Tor then it doesn't
even need to know who they are.

The second feature is similar, but it uses Alice and Bob's mutual
contacts as repeaters. If Alice, Bob and Carol are all contacts, and
if they all /know/ that they're contacts (for example, because Alice
introduced Bob to Carol), then Alice can connect to Carol and upload a
blob of encrypted data for Bob, and later Bob can connect to Carol and
download it. Again, Carol can't read the data.

Hope this answers your question.

Cheers,
Michael

On 29/01/14 02:20, d.t...@gm... wrote:
> Hi, Michael et al!
> 
> With interest, I read the information available about briar on the
> briar web site. However, after doing so, it’s still nor clear to me
> how peers find each other (e.g. in a TCP network).
> 
> When I do the routing myself by sending e.g. USB-Sticks, it’s ok,
> but how to connect to my friend to deliver a message to him in a
> TCP network where he might be offline most of the time and my
> sending node is offline at times.
> 
> Would my sending node just send the messages to any node(s)
> available and hope the flooding does the rest?
> 
> How do nodes discover each other?
> 
> Greetings, g3ntleman 
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>
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