What Is the Concept of “Finality” in a Blockchain and How Does a 51% Attack Challenge It?
Finality refers to the guarantee that once a transaction is recorded in a block, it cannot be reversed, altered, or removed from the blockchain. In Proof-of-Work, finality is probabilistic, increasing with each subsequent block (confirmations).
A 51% attack directly challenges this by enabling the attacker to create a longer, alternative chain that excludes the original transaction, effectively reversing it. This breaks the fundamental assumption of immutability and finality that underpins the network's trust.
Glossar
Probabilistic Finality
Certainty ⎊ Probabilistic finality within cryptocurrency and derivatives represents a quantified assessment of settlement irreversibility, diverging from traditional absolute finality models.
51% Attack
Dominance ⎊ The 51% attack, within cryptocurrency contexts, represents a scenario where a single entity or coalition controls more than half of a blockchain network's hashing power or stake.