Monero With Multi-Grained Redaction

Monero is a privacy-centric cryptocurrency that allows users to obscure their transactions with multiple input and output addresses. Current research on Monero mainly focuses on identifying design vulnerabilities or optimizing towards stronger privacy, security, etc. For example, improving the design of ring confidential transaction (RingCT) protocol proposed by Noether et al. As revealed by Ali et al. in USENIX 2016, new blockchains have inadequate nodes and network computing resources to resist powerful attack (e.g., 51% attack). Obviously, Monero blockchain is not an exception. Ateniese et al. proposed the notion of redactable blockchain in EuroS
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P 2017, which begins the trend of formalizing blockchain with extra cryptographic primitives. The motivation is to turn an immutable blockchain into a mutable ledger by adapting the blockchain design and integrating with new cryptographic schemes. In such a setting, users could use their private keys to perform the secure multi-party computation to reverse blockchain history. The idea of redactable blockchain has attracted many researchers to pursuit this topic. However, few works have considered the privacy-preserving setting. Even fewer have practised their designs in an actual cryptocurrency. In this paper, we seek to adapt the RingCT protocol with several building blocks. Our proposal achieves most of the desired properties for blockchain redaction. It allows multiple tracing authorities to collaboratively trace users’ identities, and a system manager to perform multi-grained (including block-level, transaction-level, accumulator-level and commitment-level) redaction on block contents. Our proposal can be seen as an extension of RingCT protocol. We give rigorous security requirements and comprehensive analysis of our scheme. The performance evaluation suggested that our scheme suffers from some unscalabilities in large-scale implementations. A more elegant design to achieve stronger security and ideal scalability is deemed as a challenging and interesting future work.