How Does “Proof-of-Work” Secure a Blockchain?

Proof-of-Work (PoW) secures a blockchain by requiring miners to expend significant computational effort (hash power) to solve a complex mathematical problem to create a new block. This effort makes it prohibitively expensive and energy-intensive for a malicious actor to gain control of the network (the 51% attack).

The longest chain of blocks is accepted as the valid history.

What Is the Relationship between the Block Reward and the Security Provided by the Longest Chain Rule?
What Is a “51% Attack”?
How Does ‘Nakamoto Consensus’ Enforce the Longest Chain Rule?
What Is the ‘Longest Chain Rule’ in Bitcoin?
What Is the ‘Longest Chain Rule’ and Why Is It Fundamental to Nakamoto Consensus?
How Do Forks, Both Accidental and Malicious, Relate to the Longest Chain Rule?
Define “In-the-Money” (ITM) for a Call Option.
What Is the Difference between the “Longest Chain Rule” and the “Heaviest Chain Rule” in PoW?

Glossar