How Does the Concept of “Proof-of-Work” Contribute to the Immutability of a Blockchain And, Consequently, Non-Repudiation?

Proof-of-work is a consensus mechanism that requires miners to solve a complex mathematical problem to add a new block to the blockchain. This process is computationally expensive and time-consuming, making it extremely difficult for a single actor to alter the blockchain's history.

To change a previous block, an attacker would need to re-mine that block and all subsequent blocks faster than the rest of the network, which would require an immense amount of computing power. This makes the blockchain effectively immutable, ensuring that transactions cannot be altered or deleted, which in turn strengthens non-repudiation.