This Week in Blockchain Research Issue #102
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Paper of the Week:
In proof-of-stake (PoS) blockchains, stakeholders that extend the chain are selected according to the amount of stake they own. In S&P 2019 the “Ouroboros Crypsinous” system of Kerber et al. (and concurrently Ganesh et al. in EUROCRYPT 2019) presented a mechanism that hides the identity of the stakeholder when adding blocks, hence preserving anonymity of stakeholders both during payment and mining in the Ouroboros blockchain.
They focus on anonymizing the messages of the blockchain protocol, but suggest that potential identity leaks from the network-layer can be removed as well by employing anonymous broadcast channels.
This work shows that this intuition is flawed. Even ideal anonymous broadcast channels do not suffice to protect the identity of the stakeholder who proposes a block.
The work shows a formal network-attack against Ouroboros Crypsinous, where the adversary can leverage network delays to distinguish who is the stakeholder that added a block on the blockchain.
It abstracts the above attack and shows that whenever the adversary has control over the network delay – within the synchrony bound – loss of anonymity is inherent for any protocol that provides liveness guarantees.
This is done, by first proving that it is impossible to devise a (deterministic) state-machine replication protocol that achieves basic liveness guarantees and better than (1 − 2f ) anonymity at the same time (where f is the fraction of corrupted parties).
Then connecting this result to the PoS setting by presenting the tagging and reverse tagging attack that allows an adversary, across several executions of the PoS protocol, to learn the stake of a target node, by simply delaying messages for the target.
The paper shows that the attacks are practical, by describing how they can be carried out over the Zcash blockchain network (even when Tor is used).
In conclusion, approaches are suggested that can mitigate such attacks.
1. Paper Title: History Binding Signature.
Summary: A single private/public key pair signature scheme using verifiable random function, that binds a signer to its signature history.
Affiliations: * Ben-Gurion University of the Negev.
Summary: New cryptographic techniques to integrate security policies (developed in the traditional banking domain) in the blockchain settings.
Authors: Florian Breuer*, Vipul Goyal†‡, and Giulio Malavolta§,
Summary: While the LN has the potential to also become a privacy-preserving tool, recent work has demon- strated that the existing public payment channel network leaks private information about payments.
Summary: A privacy-preserving cross-chain platform to enable confidential interoperability across blockchains.
Affiliations: * Peking University.
Summary: A novel SNARK-based construction that allows Bitcoin-like blockchains to create and communicate with sidechains of different types without knowing their internal structure.
1. Paper Title: Categories and Functions of Crypto-Tokens.
Summary: Major issues concerning the economics of using tokens including platform finance, user adoption, stablecoins, crowdsourcing, and agency issues, with legal and regulatory implications, and finally
Authors: Lin William Cong* and Yizhou Xiao†,
2. Paper Title: Fertile LAND: Pricing non-fungible tokens.
Summary: The pricing of parcels of virtual real estate in the largest blockchain virtual world, Decentraland; an NFT simply termed LAND.
Authors: Michael M. Dowling*,
Affiliations: * Dublin City University Business School.
Summary: The fairness of incentives for several blockchain protocols, including PoW, ML-PoS, SL-PoS and C-PoS.
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