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

Blockchain, Cryptographic immutability, Cryptographic timestamping, Proof-of-sequential-work
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