What Is ‘Finality’ in Blockchain Transactions and How Does a 51% Attack Violate It?
Finality refers to the guarantee that a transaction, once confirmed, cannot be reversed or altered. In PoW, transactions achieve probabilistic finality after a sufficient number of subsequent blocks are added.
A 51% attack violates this by creating a longer, secret chain that includes a double-spend transaction, then releasing it to the network, forcing a chain reorganization (reorg). This reverses the original transaction, nullifying its perceived finality.
Glossar
Transaction Finality
Principle ⎊ Transaction finality is the principle that once a transaction is recorded on a blockchain, it cannot be reversed, altered, or canceled, providing absolute and irreversible settlement assurance.
Probabilistic Finality
Certainty ⎊ Probabilistic finality within cryptocurrency and derivatives represents a quantified assessment of settlement irreversibility, diverging from traditional absolute finality models.
Consensus Mechanisms
Validation ⎊ Consensus mechanisms, within cryptocurrency, establish trust and secure transaction records without a central authority, fundamentally altering traditional financial infrastructure.
Block Depth
Depth ⎊ The concept of block depth, across cryptocurrency, options, and derivatives, fundamentally quantifies the number of blocks or periods required for a transaction or derivative contract to achieve finality, representing a measure of temporal security and irreversibility.
Chain Reorganization
Blockchain Fork Resolution ⎊ The process by which a network resolves a temporary divergence in the transaction history, typically resulting in the abandonment of the shorter chain in favor of the one with greater cumulative proof-of-work.