Scalable and Redactable Blockchain with Update and Anonymity

Abstract Internet-of-Things (IoT) envisions communications between heterogeneous devices and utilization of the associated data for smart decision making. Blockchain bridges the gap between widely-distributed IoT devices and the need for a universal trust-layer. When applying blockchain for IoT, some concerns can arise. Among them, scalability is a crucial factor because it decides whether blockchain can keep empowering IoT in the long term . According to a recent survey by Ali et al., some newly launched blockchains are suffering from powerful attacks (e.g. 51% attack) when the computing pool is small, and the number of participated nodes is inadequate (USENIX 2016). To ensure the scalability of initially-deployed blockchains, a proper countermeasure is important to be devised. Ateniese et al. proposed the notion of the redactable blockchain (EuroS&P 2017) which allows block history to be rewritten by using chameleon hash. However, the distribution and management of trapdoor key is crucial for the scalability of chameleon hash as well as redactable blockchain. To deal with the above problems, we propose two cryptographic schemes as the new theoretic tools for blockchain redaction: time updatable chameleon hash (TUCH) and linkable-and-redactable ring signature (LRRS). The use of TUCH and LRRS schemes enables redaction to take place scalably and anonymously where the spontaneous ring is generated for redaction, which costs little expenditures to rewrite a block content. Specifically, the redaction will be processed without assigning and splitting trapdoor key among multiple users in a complex way, and achieve transaction anonymity for users . What is more, we briefly instantiate how to build a redactable blockchain with update and anonymity (SRB) with our proposed TUCH and LRRS. While security analysis confirms that our proposals are theoretically secure, the experimental results show that our proposals are efficient for implementation purposes.