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Neighbour-Net Proxy Protocol
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README.md
rfc4685.txt

README.md

Introducing the Neighbour-Net Proxy Protocol

Goals

  • To implement tools for users to construct and maintain social networks a la Facebook and Twitter, in a decentralised distributed privacy-aware fashion with builtin redundancy if nodes go off-line or are compromised.

    • status updates and "public walls"
    • "blog" posting for the publication of news, articles, and essays
    • public and semi-public discussion forums
    • private/direct messaging a la email
  • To allow people to keep their content in their own house instead of at the mercy of third parties "in the cloud". See http://www.softwarefreedom.org/events/2010/isoc-ny/FreedomInTheCloud-transcript.html

  • By means of caching, be reasonably performant for people who want to read that content, without requiring everyone to have "5 9s" uptimes for their own hardware in their own living rooms.

  • Make some attempt at being robust against DNS shutdowns or poisoning.

  • Use existing standards where possible.

Non-goals

The following are not goals. No judgement on whether or not they are desirable goals is intended by their omission, but they are different problems from the problems which this proposal sets out to solve.

  • We are not in the business of providing an API for "Facebook App"-style third party web-page-in-a-frame applications.

  • We are not catering for use cases where anonymity is important. Your identity in this system may or may not correspond to your local government's record of your identity, but it is still your identity.

  • We are largely assuming you are operating in a place where the rule of law is mostly upheld.

Architecture

  • an Atompub server with pervasive xml-enc/xml-dsig (based on PGP)
  • which includes an http caching proxy open to our friends
  • and participates in a distributed hash table mapping node addresses (actually PGP key fingerprints) to IP addresses
  • the DHT also to be interrogable via the DNS protocol

Node

A node corresponds more or less with a user. It may run on hardware they have at home (the Freedom Box vision) or on shared server/virtual server space somewhere. Or even on a smartphone (this may not be a good idea if you're going to lose the phone). Basically, anywhere with an Internet connection.

Each NNPP node is an HTTP origin server and a proxy which will cache resources from neighbours. "Neighbours" are typically resources linked to from local content, or available from ATOM feeds to which the node owner has subscribed.

An NNPP-aware browser identifies an NNPP-aware server by the presence of a 'Cache-Control: public, nnpp-cache-links' header on its responses. It may then submit proxy requests to the same server for further content that it thinks the server is likely to hold. It must use an 'Cache-Control: only-if-cached' header on these requests [or something like it: might not want to usurp that token if there are legitimate reasons for using it]. The server may respond from cache (subject to normal HTTP cacheability rules) or by forwarding a request from upstream, or may reject the request ("504 Gateway timeout") if it doesn't want to serve that document.

Content

The local content available from a node is defined by an Atompub service document. Various collections may exist to group resources for different audiences (e.g. Whiteboard, Public, Work, Family, Friends, Clubmembers, Inbox). Whiteboard, Inbox and Public have special semantics

  • Public - others can see this, the owner can post
  • Whiteboard - others can see this, others can post (like a facebook wall)
  • Inbox - owner can see this, others can post (a "private message" feed)

"Others" in all three of these cases is user-defined according to preferred privacy settings.

[ to make this a credible email alternative there will need to be provision either for tagging inbox messages or for rule-based routing them ]

Other collections may be created ad-hoc for other purposes: users might wish for example to create special-interest collections to avoid spamming "normal" friends with "geek" interests, or vice versa

Remotely created content which is cached here may also be described in a similar way: we keep a Collection in which each entry is one of our friends' service documents, and clients may expect that an HTTP proxy request to this node for any document contained in those feeds will be answered.

Security

We use xml-enc,xml-dsig to PGP-(encrypt,sign) each entry when it is destined for a limited-access audience. The corresponding private key is given to each member of the group being posted to [ how? ] and changed if a group member is to be evicted [ again, how? ]

Note that each collection defines an http-addressable Feed document, by atompub decree. The information that a new document has been posted to a classified feed may itself be classified, so these feed resources must be regenerated and re-encrypted whenever they change. We can limit the work involved here by making them partial feeds with only a few entries, and by making them link to the entries instead of including them (but I think APP dictates this latter choice anyway)

[ need to sort out all the mechanism for how to get the key and signing it and all that jazz. ]

Public keys should be stored by the node when first encountered. They can be cached by intermediaries just like any other document, but if there is no trust relationship between the nodes then the client UA should caution the user that the document is not verified. To reiterate that last point: the pubkey can be cached according to the same rules as everything else, because it's the trust web that matters.

This proposal currently assumes that PGP keys correspond to nodes and not directly to users. Thus, if you also have a mobile device (e.g. smartphone) that you want to participate in the system, it becomes an independent node and can be independently revoked if it is lost or taken from you. There are several annoying niggly bits here I haven't fully explored: what happens if someone sends you a private message encrypted to your home node and you are not at your home node? I think the answer will be that your default identity is in fact a group, so your friend should encrypt for all of your multiple keys unless he specifically wants to send you something (perhaps a particularly sensitive document) that you can read only at home.

Bootstrapping/DNS

If a node is publishing controversial material, an offended party may attempt to make it inaccessible by putting pressure on the DNS provider. DNS in any case is a faff for people whose primary nodes are connected with dynamically assigned IP (DSL, dialup, mobiles).

We identify nodes by their PGP key. We make the key fingerprint the basic unit of addressing, and the PGP key name becomes the friendly node name. Then we can give all nodes addresses of the form

  • 1297D4B5.node.nnrp.net (shorthand for convenience)
  • 13D702AD866527E08F715326776FD7C0.1297D4B5.node.nnrp.net (unambiguous)

and implement a DHT mapping node addresses to IP addresses, which nodes will use internally in preference to ordinary DNS. A node may also be a public DNS server for this zone, and the published zone file can contain as many relatively stable nodes as we want. For the most part we only need conventional DNS when fetching from new nodes that we have no previous contact with, so there shouldn't be major outages if that blows up.

To avoid dns cache poisoning or similar attacks, after fetching a resource from a node, the client must verify that the fingerprint matches.

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