Sunday, January 27, 2008

A security thought: AT&T Copyright Fighting

The following is just my own opinion and speculation, to a hypothetical question: If I was AT&T, why and how would I implement the AT&T plan to enforce copyright on user traffic. (Note, this post is an extension of my slashdot comment on that thread, and basically describes a "DMCA Takedown on the Network Layer" style of response.)

I also believe this would be a significant problem if implemented. I'm a believer that general network neutrality is a mostly good thing. But when a company seriously proposes filtering, I believe we should attempt to determine what shape such filtering would take, and how it could maximize the stated objectives while minimizing collateral damage. This also gives those opposed to filtering a leg up on attempting to counter it.

To begin with, AT&T probably has a huge incentive to block pirated traffic. Time-Warner cable supposedly has 50% of the bandwidth used by 5% of the users. Who wants to bet that of this bandwidth, it is almost all pirated material and/or pornography? As an ISP, wouldn't you want to remove 1/3rd of your traffic? Especially if its customers that can't really complain about it?

The strength of piracy on the Internet is the ease of getting the pirated material,and the ease of distribution. Thus pirated material must be easy to find if it is to be a substantial portion of traffic and to have a significant economic impact.

So all the MPAA has to do is find the easy-to-find content, and do something about it. Currently, they've tried playing Whak-A-Mole on the Torrent tracking servers, but this has been a losing game, as these servers have already fled to "Countries of convenience", where they are difficult for the MPAA to sue off the network.

But rather than playing Whak-A-Mole on Torrent tracker servers (which are largely offshore), with ISP cooperation from AT&T it becomes possible to play Whak-A-Mole on the torrents themselves. Such a system would benefit both the content owners and the ISPs.

All that is necessary is that the MPAA or their contractor automatically spiders for torrents. When it finds torrents, it connects to each torrent with manipulated clients. The client would first transfer enough content to verify copyright, and then attempt to map the participants in the Torrent.

Now the MPAA has a "map" of the participants, a graph of all clients of a particular stream. Simply send this as an automated message to the ISP saying "This current graph is bad, block it". All the ISP has to do is put in a set of short lived (10 minute) router ACLs which block all pairs that cross its network, killing all traffic for that torrent on the ISP's network. By continuing to spider the Torrent, the MPAA can find new users as they are added and dropped, updating the map to the ISP in near-real-time.

This would be a powerful system, and the likely solution AT&T will use if they carry through on their plans to enforce copyright:

  • This requires no wiretapping. Instead, it relies solely on public information: the torrent servers and being able to contact participants in order to map those fetching an individual file. BitTorrent encryption would have no impact on this scheme.
  • It can be completely automated, both for the MPAA and AT&T
  • It also minimizes collateral damage, since only participants in an individual torrent can't communicate with each other when a Torrent is blocked. If the MPAA actually spiders the torrent (rather then trusting information from the trackers), there should be no false edges in the graph. The only collateral damage is if a pair of systems is also performing legitimate communication at the same time they are participating in the Torrent, something the ISP probably considers acceptable.
  • Any real collateral damage (incorrectly blocking content) AT&T can say is the fault of the MPAA.
  • It should be robust in the arms race: if the pirated material is open and distributed in a P2P manner, the MPAA's spiders should be able to track it. (Remember, even if CAPTCHAs are used to protect trackers or aspects of the systems, solving a CAPTCHA only costs $.01).
  • And its inexpensive. All AT&T has to do is deploy a small program to set and release a bunch of router ACLs, and thats it. AT&T can even keep the number of ACLs reasonably low, because they expire quickly and only need to be partially effective. No new hardware is required and everything can be fully automated. All the real costs (of spidering the Torrents, content identification, affirming that it is actually a copyright violation, and constructing the graphs) is placed on the MPAA or their contractor.

Likewise, (IANAL) AT&T can possibly avoid most liability. They aren't doing any wiretapping, nor even making a decision about which traffic to block.

Finally, AT&T has a huge number of reasons to deploy such a system:

  • It keeps the content providers happy for when they are negotiating their compete-with-iTunes/Netflix video on demand and cable TV services.
  • It keeps the content providers from pushing through very draconian legislation, or at least draconian legislation you aren't happy with. (It can F-up your competitors, but thats just a bonus)
  • And it drops their bandwidth bills by 30-50% by eliminating a large amount of deliberately-noncacheable (both politically and because of bittorrent encryption) traffic.

This won't stop closed-world pirates, those with a significant entry and secrecy, but those are far less significant. Closed-world pirates are much lower bandwidth for the ISP, because its far more difficult for pirates to get the content. But it should be able to shut down Bittorrent for open-world piracy, without blocking legitimate BitTorrent. It also won't stop child porn, although AT&T would probably claim that it does.

This was speculation. I have no evidence that this is what AT&T is planning. But given the huge expense (deep packet inspection), legal implications (wiretapping, false positives) and limitations (cryptography), I find it doubtful that AT&T really wants to detect copyrighted material directly. Performing deep packet inspection at line rates, especially to match a large database of copyrighted material, is hugely expensive, and would fail in the presence of encrypted Torrents and SSL-equipped Torrent search servers.

Thus I'm almost certain that if AT&T truely wishes to carry forward with its copyright-enforcement plants, the system will be similar to the one I've described.

Detecting this if they do deploy copyright enforcement would be possible, by participating in torrents (to generate the block) and then checking how that affects connectivity. If AT&T blocks Torrents but other TCP connectivity in those port ranges remains between two hosts, they aren't using only the speculated system, instead they would have to be directly inspecting the traffic between the hosts to determine that an individual flow is participating, information which can only be obtained by directly monitoring communication between the two hosts.

EDIT/addition: Richard Bennet has also discussed this technique at the Network Neutrality forum on 1/26/2008 (Slides at Richard Bennet's web site, on how easy it is to find pirated materials and participating peers to tell the ISP what to block).

He also brings up the important question: "Is there any reason that such an automated system should not be used, or does Net Neutrality now connote a license to steal?" This is a tough argument to counter.

The ongoing discussion can be viewed at The NNSquad Mailing List archive.

EDIT/addition #2: Delayed release of keys (distribute then release keys, as Richard Clayton pointed out) would slow down any spider, but also slows down users from getting content. The spider could still block all users after the key is released, and as people couldn't tell what they are downloading BEFORE the key is released, the MPAA could produce a large number of poisoned (false data) torrents during this window.