The cost of a supernode is more than just monetary. There is a cost to the network when one single entity controls all the supernodes, because in almost all cases that means they have some disproportionate level of power over routing or quality of service. You wouldn&#x27;t want one company running every Tor exit node, because then it&#x27;s not decentralized.<p>A business model that relies on donations to one, or a few, entities controlling the supernodes perpetuates the centralization of infrastructure. Not to mention that donations are historically the most cost inefficient solution, especially compared to &quot;market forces.&quot; If the efficiency of a decentralized system depends on the number and quality of supernodes, then some economic mechanism must exist to incentivize peers to become &quot;super peers.&quot; The competition will ensure that the super peers who survive are the ones with the highest quality nodes at the lowest cost.<p>Then the question becomes, who pays the cost that gets distributed to the supernodes? In the case of TorCoin, we wanted to avoid the situation  where people need to pay to join the Tor network. So our solution was a cryptocurrency with &quot;proof of bandwidth&quot; as its &quot;proof of work.&quot; Just like a single Bitcoin represents some amount of CPU power that was expended to &quot;mine&quot; the BitCoin, a single TorCoin would represent some amount of bandwidth that was transferred to &quot;mine&quot; the TorCoin.<p>The idea was that a TorCoin would have value outside of Tor, and Tor was simply the mechanism used to mine it. So relay operators would mine TorCoins, then sell them on an exchange just like they would any other altcoin. This way they get value from providing bandwidth to Tor users, but the users do not need to pay for the service.<p>However this gets complicated very fast, because you&#x27;re not talking about one person mining coins with one CPU, but pairs of people mining coins by transferring bandwidth between each other. So the priority of the paper was addressing the threat of collusion, where two malicious nodes (possibly controlled by the same actor) spoof terabytes of bandwidth between each other, flooding the market with TorCoins. Our key insight was &quot;TorPath,&quot; a circuit selection mechanism that ensures every circuit participating in the TorCoin mining scheme is &quot;privately-addressable but publicly verifiable.&quot; So each TorCoin (or part of a TorCoin) would represent a circuit that actually existed, and anyone could verify that via a public ledger, without revealing the identity of the circuit participants.<p>I think the idea of non-CPU &quot;proof of work&quot; schemes is very interesting in general, and bandwidth is one of the most profitable venues to apply it to. For example, imagine if the BGP system were operated along an incentive scheme like this, where instead of &quot;circuits&quot; we are talking about &quot;peering.&quot; The path selection mechanism we devised would work in any routing system with multiple participants, not just Tor.