BA-05 · LESSON 07

Confirmations and finality

Confirmations measure accumulated proof of work after inclusion; required depth depends on value, threat model, and protocol configuration.

55 min Difficulty 2/5 Not started

VISUAL MODEL

See the whole mechanism before going step by step

Use the diagrams to orient yourself. Then the guided explanation below teaches every part in depth.

4 explanatory views

CONCEPT-SPECIFIC MAP · transaction bytesA transaction consumes prior outputs and commits new onesSelect any state to inspect its exact role.

RELATIONSHIP MAPInputs, rule, and outputs

01
OUTPOINTSTxid : output index
Every input references one specific prior transaction output.
02
AUTHORIZATIONWitness or scriptSig
Spending data satisfies the prior output's locking condition.
03
SERIALIZATIONConfirmations and finality
The Confirmations and finality mechanism determines which transaction fields or identifiers matter.
04
NEW OUTPUTSAmount and script
Payment and change outputs are newly created state.
05
IDENTIFIERSTxid and wtxid
Double-SHA256 identifiers commit to defined byte regions.

Rule shown: Inputs name exact outpoints; outputs allocate value; signatures authorize the committed spending context.

STAGE 1 OF 5OUTPOINTS: Txid : output index

Every input references one specific prior transaction output.

Governing relationship: Inputs name exact outpoints; outputs allocate value; signatures authorize the committed spending context. Complete path: 1. OUTPOINTS, Txid : output index. Every input references one specific prior transaction output. 2. AUTHORIZATION, Witness or scriptSig. Spending data satisfies the prior output's locking condition. 3. SERIALIZATION, Confirmations and finality. The Confirmations and finality mechanism determines which transaction fields or identifiers matter. 4. NEW OUTPUTS, Amount and script. Payment and change outputs are newly created state. 5. IDENTIFIERS, Txid and wtxid. Double-SHA256 identifiers commit to defined byte regions.

1. State transitionWhat exists, what changes, and what results

BEFORE

Transaction T is included at height 800,000. The current accepted tip is 800,005.

MECHANISM

Before inclusion, the transaction is unconfirmed and can conflict, be replaced under policy, expire from mempools, or fail to reach miners.

AFTER

Count confirmations relative to the current accepted chain and track the exact block containing the transaction.

Text equivalent: Starting from Transaction T is included at height 800,000. The current accepted tip is 800,005. The mechanism begins when Before inclusion, the transaction is unconfirmed and can conflict, be replaced under policy, expire from mempools, or fail to reach miners. The resulting lesson is Count confirmations relative to the current accepted chain and track the exact block containing the transaction.

2. Mechanism pathSelect a stage to inspect its job

STAGE 1 OF 5

Observe block inclusion

Before inclusion, the transaction is unconfirmed and can conflict, be replaced under policy, expire from mempools, or fail to reach miners.

Complete path: 1. Observe block inclusion: Before inclusion, the transaction is unconfirmed and can conflict, be replaced under policy, expire from mempools, or fail to reach miners. 2. Count depth: If a transaction is in block height h and the tip is height H on the same chain, confirmations equal H minus h plus one. 3. Model a competing history: A reorganization disconnects blocks when another valid branch gains more accumulated work. Transactions from disconnected blocks return to an unconfirmed or conflicted state if still valid. 4. Choose a risk threshold: Appropriate confirmation depth depends on payment value, attacker capability, transaction signals, counterparty, service, and cost of reversal. 5. Monitor rather than declare certainty: Even deeply confirmed transactions have nonzero reorg probability. Applications should define explicit handling for reorgs and conflicting state.

3. Rule and failure boundaryWhat accepts the result and where it can stop

ACCEPTED PATH

The accepted branch is selected by accumulated work, confirmations are recomputed from its exact inclusion height, and the application records confirmed, unconfirmed, or conflicted state.

CHANGED CONDITION

A deeper reorg that disconnects the containing block removes confirmations; a conflicting replacement marks the payment conflicted rather than merely zero-depth.

Important distinction: Six confirmations make a Bitcoin transaction mathematically irreversible. Six is a common risk convention, not a consensus finality boundary. Reversal becomes less probable and more costly as work accumulates.

Text equivalent: The accepted path is enforced by The accepted branch is selected by accumulated work, confirmations are recomputed from its exact inclusion height, and the application records confirmed, unconfirmed, or conflicted state. If the required condition changes, A deeper reorg that disconnects the containing block removes confirmations; a conflicting replacement marks the payment conflicted rather than merely zero-depth.

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Learn the idea

A confirmation means a transaction is included in a block on the node's accepted chain. Its first confirmation is that block; each valid descendant block adds one. More confirmations represent more accumulated proof of work built after the transaction. They reduce reorganization risk but do not create absolute finality.

GUIDED EXPLANATION1/5 ideas inspected

Observe block inclusion

Before inclusion, the transaction is unconfirmed and can conflict, be replaced under policy, expire from mempools, or fail to reach miners.

The worked example follows the explanation

Inspect every idea above to open it.

Important distinction“Six confirmations make a Bitcoin transaction mathematically irreversible.”

Six is a common risk convention, not a consensus finality boundary. Reversal becomes less probable and more costly as work accumulates.

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