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My understanding is that IPFS and Bittorrent Mainline DHT are built on top of a Distributed hash Table (Kademlia). They use the file hash as Kademlia key to find a list of peer that might have this file.
1- What I don't understand is if this is all decentralized who remove from the DHT peer that no longer host a file content?
2- What prevent someone from storing large amount of data for free inside the DHT?
3- What prevent someone from disrupting the network by adding large number of invalid peer for a popular file.
4- What prevent a bad actor from joining the DHT ring and not following the routing protocol thus preventing discovery message from reaching correct nodes.
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Why Is a Distributed Hash Table Used? Distributed hash tables provide an easy way to find information in a large collection of data because all keys are in a consistent format, and the entire set of keys can be partitioned in a way that allows fast identification on where the key/value pair resides.
IPFS takes SHA256(PeerID) and interprets it as an integer between 0 and 2^256-1 . A projection that will take a record key and calculate a position in the address space where the peer or peers most ideally suited to store the record should be near. IPFS uses SHA256(Record Key) .
In computing, Chord is a protocol and algorithm for a peer-to-peer distributed hash table. A distributed hash table stores key-value pairs by assigning keys to different computers (known as "nodes"); a node will store the values for all the keys for which it is responsible.
Not sure why this was downvoted. These are excellent questions.
1- What I don't understand is if this is all decentralized who remove from the DHT peer that no longer host a file content?
I think that DHT entries are regularly re-broadcast. So if a peer goes away, its DHT entries will no longer be broadcast and the network will forget about the data it provides unless some other node has it.
2- What prevent someone from storing large amount of data for free inside the DHT?
Unless you re-publish or somebody else is interested in the data, it will vanish. The amount of data that you can store directly in a DHT entry is limited. So you can make other nodes store some of your data by putting data directly into DHT entries, but the effort outweighs the benefits.
3- What prevent someone from disrupting the network by adding large number of invalid peer for a popular file.
I think there are some mechanisms envisioned in IPFS to protect the DHT against attacks. However, I don't think the current implementation is all that sophisticated. I don't think that current IPFS would deal well with a large scale distributed DDOS attack.
4- What prevent a bad actor from joining the DHT ring and not following the routing protocol thus preventing discovery message from reaching correct nodes.
I think a single node would be insufficient to do much damage, because a node will ask multiple peers. You would have to have multiple nodes to do significant damage.
But IPFS as it is now would not survive a sophisticated attack by state actors.
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