wiki:NetDB/NextBackend

Version 21 (modified by hottuna, 6 years ago) (diff)

General P2P networks

Name Search horizon* Comments
Gnutella Limited
Gnutella2 Limited


  • Search horizon describes how much the network that can be searched from a certain position in the network graph. Limited search horizon means that a search from one part of the network won't necessarily find results from another part of the network.

DHTs

DHTs are a good alternative due to O(log n) lookup time and a unlimited search horizon. But have serious issues when it comes to being robust against attacks.

Name Search horizon* Lookup steps Mutable data Comments
Kademlia Unlimited Max: O(log2 n)
Min: O(log2b n)
No Is susceptible to sybil and eclipse attacks.*
Freenet Unlimited O(log2 n) [2]No
Choord Unlimited No Is highly susceptible to sybil and eclipse attacks.*
Pastry Unlimited No Is highly susceptible to sybil and eclipse attacks.*


  • Kademlia is less susceptible to eclipse attacks. "For one thing, it is difficult to affect the routing tables of a Kademlia node, as each node tends to keep only highly available peers in its routing table. This increases the required costs for an attacker to convince honest nodes to link to the compromised nodes. Similarly, Kademlia uses iterative routing, exploring multiple nodes at each step, making routing less dependent on specific nodes and thus less vulnerable to attacks." [1]

Kademlia lookups can be optimized by enlarging how many bits of IDs, b, that are considered for each bucket. With b > 1 lookup steps would be decreased from O(log2 n) to O(log2b n) but the number of buckets would be increased to an expected 2blog2bn. [2]


Kademlia Defence Mechanisms

Sybil Defence

Sybil attacks are based in the idea of creating a large number of participating nodes. The Sybil attack does not damage the DHT by itself, but can be used as a vector to artificially create a major- ity of colluding malicious nodes in the overlay.

Name Source Description

Eclipse Defence

Eclipse attacks are attacks on the routing / routing tables.

Name Source Description
Random lookups R5N[4] Before initiating a recursive kad lookup, do a random walk in the network graph to determine the start of the kad lookup.
Control in/out-degrees [5][1] Control of the in-degree and out-degree of nodes via anonymous auditing. At the cost of slower avg. lookups.

Storage Defence

Storage attacks are attacks which attempt to provide bogus responses to queries.

Name Source Description
Recursive lookups R5N[4] By making each node in a FIND_VALUE request forward the query recursively and (recursively, to the previous requester in the chain of the recursion) return the answer, a reliability metric of nodes can be obtained. Which can be used in conjunction with the last_seen attribute of k-bucket entries to create a combined eviction policy.

Kademlia Performance Improvements

Standard Kademlia performance can be improved by modifying it.

Name Source Description
Recursive lookups [6] Make FIND_VALUE request recursive by forwarding the query recursively and returning the answer directly to the original source of the request.



[1] A Survey of DHT Security Techniques _
[2] Kademlia: A Peer-to-peer information system based on the XOR Metric _
[3] Searching in a Small World _
[4] R5N : Randomized Recursive Routing for Restricted-Route Networks _
[5] Eclipse attacks on overlay networks: Threats and defenses _
[6] R/Kademlia: Recursive and Topology-aware Overlay Routing _ slides

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