ChiFS - File Sharing over Tor
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PrivateCommunities.md 2.6KB

Private Communities

With the current model, each Share is public and is sharing all of its files with anyone who might be interested in them. A Share announces itself to one or more Hubs, but those Hubs are not necessarily the only ones indexing that particular Share. In fact, it would be relatively trivial for a Hub to fully clone another Hub: Just grab a list of all Shares from the Hub and index those. A Share has no way to restrict which Hubs are allowed to index it and/or who is allowed to download from it.

Reasons for wanting to restrict access to Hubs and Shares could be:

  • A Share only has limited bandwidth and wants that bandwidth to be used by people that they know or people who benefit the most from the shared files.
  • A minority group or fandom wishes to share files amongst themselves without attracting outside attention. E.g. Furries, Bronies, etc.
  • The shared files may contain sensitive information that should not leak outside of a small community. E.g. security research, whistleblowers.

I consider this out of scope for the early stages of ChiFS, but support for private communities can be considered if there’s demand for it. Here’s a rough idea of how this could work.

Architecture

Precondition: Users have a way to register and authenticate to a Hub. Plain old user/password authentication would suffice for this model, but stronger schemes could also be supported.

The Hub generates a public/private key pair and makes sure that the public key is available to all Shares indexed by the Hub. Users that wish to download a file from a Share first obtain a token signed by the Hub’s private key, which they can then use to authenticate themselves to a Share. The Share can verify the validity of the User’s token by checking it against the public key of the Hub.

A User’s token should be short-lived, anywhere between 5 minutes and 24 hours should suffice, depending on the Hub’s policies. A short expiration time ensures that Users will have to regularly re-authenticate themselves to the Hub and limits the amount of time that a user can access Shares after their authorization has been revoked. Short-lived tokens also avoid the need to implement systems like CRL or OCSP.

Tokens could be restricted in various ways:

  • A general token to allow a user to download anything from any Share. This is just a verification that the user is registered with the Hub and is authorized to download things.
  • A token to only download from a particular Share; This way the Hub can restrict users to only access particular Shares.
  • A token to only download a single file. For extra fine-grained access control.