Last Tuesday we meet again to discuss different attacks and possible countermeasures for distributed hash tables. More in particular we looked at Kademlia and its security extension S/Kademlia [1], possible eclipse attacks on the Ethereum network [2], a novel approach of hiding its own connection buckets as well as using an existing social graph as a network topology in the Whanau paper[3], security extensions to the Chord DHT [4], as well as a larger study of different security techniques for DHTs [5].

The attacks mentioned in the papers go from the simple identity stealing, to the well known eclipse and related adversarial routing attacks, sybil attacks, denial of service and churn attacks as well as attacks on the data storage.

While the identity stealing attack is easy to solve with the help of public-key cryptography, most of the others are based on the fact that in peer-to-peer networks there is no global trusted authority granting access, thus generating new identities is cheap and fast. When introducing a central authority is not an option, one can make identity generation harder by introducing crypto puzzles [1], binding identities to IP addresses [2] or depend on reputation systems.

Within a Kademlia DHT, queries converge towards the same path when searching for a node or value. With this in mind an attacker would need to only control some nodes at the right place within the key spectrum to control answers to queries for a certain key range. The S/Kademlia [1] paper suggests to enforce disjoint lookup paths making those adversarial routing attacks less likely to succeed.

The evaluation of S/Kademlia in the simulation frame-work OverSim has shown, that even with 20% of adversar-ial nodes still 99% of all lookups are successful if disjointpaths are used

For more info, see [1] directly.

A countermeasure against data storage attacks would be to enforce that a given key would always need to correspond to the hash of its value. While this makes targeted storage requests a lot harder, it defeats the use case of the DHT as a lookup service where the key is a known string not based on the value.

Instead when issuing a storage request, one can: (1) use the hash of the key to enforce a uniform distribution and (2) send the plaintext key along with the request as an attestation for proper hashing, making the generation of keys within a certain range a lot harder.

[1] Baumgart, Ingmar, and Sebastian Mies. “S/kademlia: A practicable approach towards secure key-based routing.” 2007 International Conference on Parallel and Distributed Systems. IEEE, 2007.

[2] Marcus, Yuval, Ethan Heilman, and Sharon Goldberg. “Low-Resource Eclipse Attacks on Ethereum’s Peer-to-Peer Network.” IACR Cryptology ePrint Archive 2018 (2018): 236.

[3] Lesniewski-Laas, Christopher, and M. Frans Kaashoek. “Whanau: A sybil-proof distributed hash table.” (2010).

[4] Fiat, Amos, Jared Saia, and Maxwell Young. “Making chord robust to byzantine attacks.” European Symposium on Algorithms. Springer, Berlin, Heidelberg, 2005.

[5] Urdaneta, Guido, Guillaume Pierre, and Maarten Van Steen. “A survey of DHT security techniques.” ACM Computing Surveys (CSUR) 43.2 (2011): 8.