But they aren't instrumental! Maybe only four actually sent the file, and even a judge can be made to understand that one of those was superfluous. If you want

But they aren't instrumental! Maybe only four actually sent the file, and even a judge can be made to understand that one of those was superfluous. If you want to make it even less clear, then imagine that the client is told they can download chunks from ten peers, of which five have relevant data, if which any three are sufficient. So someone comes along and downloads eight random chunks and reconstructs the bad file. If you are required to prove that a particular peer infringed a copyright by distributing a protected work, or a work derived therefrom I think you could have a hard time. I'm not sure I understand your second objection. Suppose I publish a "status" including some copyrighted work and I encrypt it such that you need a private key corresponding to the private key of anyone on my friends list to decrypt. Then it's distributed among a thousand peers (who are not my friends), such that one of my friends can download from a random twenty, receive garbage from ten, and they'll have a 30% change of being able to reconstruct the encrypted file. Can you now prove that on the balance of probabilities a peer has violated the copyright?