distributed document popularity metrics using amortizable hashcash (Re: [p2p-hackers] BitTorrent measurements / fully decentralizedsystems)

Hal Finney hal at finney.org
Thu Dec 16 21:56:59 UTC 2004

Adam Back writes:
> I proposed a way to do this without a reputation system: amorizable
> hashcash.  http://www.hashcash.org/papers/amortizable.pdf
> It is designed to not need a reputation system. 
> There are no certificates and each user essentially gets to vote on
> the document popularity (through implicit or explicit action) in a
> distributed fashion.  To vote the user expends CPU time to create a
> hashcash stamp tied to the document id.  (Eg lower priority background
> thread during playback for implicit, for some duration as a background
> thread after marking it as quality content for explicit).

This is a cool idea but I don't exactly understand your description of
the details.

> Documents are requested from peers, and with the requester sends his
> view of the documents popularity stamp value.  The server adds the
> requesters stamp to it's own stamp, and sends the new stamp in the
> response.

The grammar here is confusing to me.  How would a requester have a stamp
before he has even downloaded the file?  I thought someone would create
a stamp after downloading, and after they have determined that the file
is legit and not bogus.

> So each peer sharing a document sums the stamps it sees, and each peer
> that downloads a document sends stamps it sees from other peers it is
> swarming from.  So (for swarming) no additional connections are needed
> for popularity metrics.  The only comms overhead is the the size of
> the stamp which is relatively compact.

The idea here is that the downloader acts as a sort of clearinghouse for
the stamps, combining them from all the peers he is swarm-downloading
from, and sending back the summed stamp to all of the peers he is
downloading from?  This way the peers all get updates from each other,
without having to connect directly to each other?

I would have thought that the stamps would be used in two ways.  First,
a prospective downloader might see several candidate files in the network
that all claim to be the one he wants.  He wants to know which are legit
and which are bogus, and the stamp value can give him a clue about this.
So he'd want to compare stamps before downloading.  And second, there then
needs to be a feedback mechanism where, after downloading and inspecting
the content, a new stamp is sent back into the network which allows the
downloader to testify that the document was good (or bad, if negative
stamps are used too).

Anyway as I said it sounds like a good idea but I am a little unclear
about the exact mechanisms and how the data would flow.  I'd appreciate
it if you could explain that again.

Hal Finney

More information about the P2p-hackers mailing list