Recently we presented a single-party cryptographic timestamping mechanism based on proof-of-sequential-work, which we proved secure in the universal composability framework. This paper describes this construction and its security claims and uses it to construct a multi-party permissioned blockchain protocol and show that it achieves an immutability notion.Finally we discuss applications of this protocol, including unpermissioned blockchains, and how these may benefit

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Reports of the European Society for Socially Embedded Technologies
ERCIM-Blockchain 2018: Blockchain Engineering: Challenges and Opportunities for Computer Science

Landerreche, E, & Stevens, M.M.J. (2018). On immutability of blockchains. In Proceedings of the 1st ERCIM Blockchain Workshop 2018. doi:10.18420/blockchain2018_04