There are a few issues with BitTorrent-like file sharing systems that make it a bad fit for the Tor network.
From the top of my head, I can think of this issues:
- You'll have to use hidden services if you want both sides of a connection to be anonymous. Such a connection involves 6 relays which means that the bandwidth used in the Tor network six times higher than the actual transfer speed.
My point is that file-sharing over Tor is the problem, because it needs a lot of bandwidth. Just like streaming youtube or netflix over Tor consumes a lot of bandwidth
Yes, they do, but unlike torrents they are still transfered at a limited speed. File sharing client will try to use all bandwidth available however. This is going to make the network unusable for anything that needs low latency, like browsing. Of course downloading files has the same effect, but having file sharing on the network could increase this kind of traffic by a few orders of magnitude.
that's why I'm looking for an answer which involves millions of bittorrent users switching to something different. Which at that scale would apparently be very bad for the Tor network.
There are few issues with having millions of users of BitTorrent or a similar software that provide relays:
- The way Tor currently informs client about available relays doesn't scale to millions of relays.
- TorBrowser, to be usable, depends on stable relays. The infrastructure to decide if millions of relays are stable and behave properly does not exist.
- It would likely make it easier for an adversary to hide malicious relays in millions of relays.
- Many of the relays are going to be very small, just a few torrent streams running over the same relay are going to make it unusable for Browsing (high delay). (Something like QoS would have to be implemented.)
Tor was designed as a low latency network, to allow it to be used for Browsing mainly. What is needed for file sharing is high bandwidth not low latency. It would probably be best to just use something that is designed for file sharing, the design of GNUnet, for instance, might be a better fit.
In conclusion, the Tor network, in its current form, is the wrong network for large-scale file sharing and it will likely stay that way for the foreseeable future.