Core Blockchain Principles Flashcards

What property of a Merkle tree allows efficient proof that a specific transaction is included in a block without downloading the entire blockchain?

Answer: Merkle proof (SPV proof)

A Merkle proof (used in Simplified Payment Verification) requires only a logarithmic number of hashes to prove inclusion without the full dataset.

In blockchain terminology, what does 'finality' refer to?

Answer: The guarantee that a confirmed transaction cannot be reversed

Finality means a transaction is irrevocably settled and cannot be altered, rolled back, or double-spent after confirmation.

Which type of blockchain fork occurs when nodes permanently diverge because they follow different protocol rules?

Answer: Hard fork

A hard fork introduces backward-incompatible rule changes, causing non-upgraded nodes to follow a different chain permanently.

What role does a cryptographic nonce serve in Proof of Work mining?

Answer: It is a number miners increment to find a hash meeting the difficulty target

Miners repeatedly change the nonce value until the resulting block hash falls below the network's current difficulty target.

What is the primary purpose of the UTXO (Unspent Transaction Output) model used in Bitcoin?

Answer: To track coin ownership by recording spendable outputs rather than account balances

The UTXO model represents value as discrete unspent outputs, preventing double-spend without requiring a global account ledger.

Which characteristic makes blockchain data immutable in practice?

Answer: Cryptographic chaining of blocks so altering one invalidates all subsequent blocks

Each block contains the hash of the previous block, so changing historical data requires recomputing all subsequent hashes—computationally infeasible on large networks.

In a permissioned blockchain, what distinguishes it from a public blockchain regarding participation?

Answer: Participation requires identity verification and explicit authorization

Permissioned blockchains restrict who can read, write, or validate transactions, requiring known identities and approved membership.