[p2p-hackers] Incentive to trade with newcomers, catch 22

[Vaste]

I want to discuss a problem with torrent and similar tradebased swarming 
networks. It is how a new peer is suppose to begin participating in the 
trade. No rational greedy peer would be interested in trading with it 
since it (naturally) has no pieces to offer in exchange. Yet, the swarm 
should (likely) benefit from it joining, providing additional bandwidth. 
Catch 22.

This has so far been solved by generosity and which works quite well. 
Yet it could be better. The problem is with a swarm generous towards 
newcomers is that it favors newcomers over regular peers. In a swarm of 
sufficient size a freerider could do quite well by downloading every 
piece from different peers, always appearing to be a new peer with 
nothing to share. The opposite, a stingy swarm, could result in new 
peers never ever being able to join the swarm.

A solution could be to let new peers transfer encrypted pieces on behalf 
of another peer. After the transfer the new peer is rewarded the key to 
the transferred piece.

Example:

A wants to transfer a piece to B and C. Seeing D is in a weak position, 
having no pieces yet, he makes a proposal. D gets to transfer the piece 
to B and C on behalf of A. D agrees. To make sure D doesn't just run off 
once he gets the piece, it is encrypted.

A transfers the piece to D who passes it on to B and C as agreed. A gets 
(some) credit from B and C for sending the piece.

A, B and C now has the decrypted piece and the key. D has the encrypted 
piece but no key. A, B and C may now ignore D; it might even be in their 
interest to keep D in a weak positition. Still, transferring the key is 
a very cheap operation and A, B or C only need some small incentive to 
do this.

E.g. A, B or C may wish to offer D to send another piece on their 
behalf. In this case it would be very unlikely for D to cooperate again, 
were they not to.

Yet, even if D were to be screwed it is still positive for the swarm as 
a whole, and D is no worse of than in the extremely stingy swarm. And 
freeriders don't thrive. (And with a little generosity D is quite well off.)

/Vaste