I was thinking about the incentive problem in DHTs.
DHTs sort of inherently mean you can’t choose which node will host your data, right? You can choose which network, but if the nodes that your key hashes to are unfriendly, they can forget you ever tried to store data on them; and so there’s no way to set up BitTorrent-like reciprocity, where other DHT nodes have an incentive to store my data so that I’ll be more willing to store their data.
I’m wondering if there’s a way to solve that problem without completely losing the desirable aspects of DHTs. In particular, node load in a DHT scales sublinearly with the system size, assuming churn is low (which is an incentive problem!), node count scales with data size, and update rate doesn’t change. That would fit in, say, 64 bytes. But nodes might discard your data item because it’s deemed to be an anti-Islamic data item, for example, if the DHT node happens to be hosted in Saudi Arabia, or a heretical data item if it happens to be hosted in a Christian country.
The data that is thus incentive-protected need not be large, because the data items can be very small and still be useful. For example, you could store a (key, favorableserver) pair that redirects querents to a server that you do have some kind of ongoing mutual relationship with, such as ownership, payment, or reciprocal storage.
One possibility is that there’s some way to ensure that the DHT node can’t erase your data with certainty without erasing everyone’s data with some probability, which converts the incentive from a relationship with only you to a relationship with the entire network. Like, if the node couldn’t tell which data was yours.
Typically, DHTs already do store your data on multiple DHT nodes to provide some resilience in the face of node churn; even Karger’s original “Consistent Hashing” paper from 1997 that Akamai was founded on explains that you can hash the URL to several different points on the circle, which will probably map to different servers; but this doesn’t really solve the incentive problem.
As another way of thinking about the incentive problem, consider the case of expiry times. You have a DHT that typically maintains object validity fo ra day. But you want to store data in it that will be consulted perhaps once a week. If your publisher is reliable, it will re-store the data in the DHT nodes about every 12 hours, which is to say about 14 times as often as it's consulted. It would be a lot more efficient on an overall basis to persuade the DHT to store your data for a week or ten instead of a day, and also be more resistant to you being arrested for publishing un-Islamic material.
DHTs suffer badly from churn, and churn in practice is pretty high, which is arguably another aspect of the same incentive problem — how do you incentivize people to keep their nodes running?
You are looking for the phrase "proof-of-storage" (which doesn't exist yet, but many people have been wondering about this under this name). Usually you can't actually guarantee storage, but you can pay people to provide proofs that they have data that you salted before giving to them.