Block 170 shows what a Bitcoin transaction actually spends

Inherited archive entry · retained from the earlier edition. Its factual, legal and policy claims have not all been reverified for 19 September 2026. Research scope.

The transaction recorded in block 170

Block 170, timestamped 12 January 2009, contains a coinbase transaction and one further transaction that spends a single 50-bitcoin input and produces two outputs: one paying 10 bitcoin to a public key, the other returning 40 bitcoin to a different public key. Hal Finney later wrote in his own account, 'Bitcoin and me (Hal Finney)', that he was the recipient of that first transaction, describing the ten coins Satoshi sent him as 'a test'. Read together, the chain data shows the mechanics and Finney's own words identify the recipient of the smaller output.

What a transaction consumes and creates

The pattern in block 170 is the pattern every Bitcoin transaction still follows. The Bitcoin developer guide describes it directly: each input spends the satoshis paid to a previous output, and each new output then waits as an unspent output until some later transaction spends it in turn. A transaction is not a transfer of a labelled coin from one party to another; it is the destruction of one or more prior outputs and the creation of new ones whose combined value cannot exceed what was consumed. The 40-bitcoin output here is ordinary change, mechanically identical to the 10-bitcoin payment; the chain itself does not mark one output as the payment and the other as the leftover, only the sender's intent, visible here only because Finney later described it, does that.

The limits of this evidence

The blockchain data proves the transaction's structure, what was spent, what was created, when, with the same certainty it proves any other transaction in the chain's history. It does not, by itself, prove who controlled either public key; that link depends entirely on Finney's own testimony, written more than four years later as part of a longer account posted after his diagnosis with a terminal illness. That testimony is a first-person recollection rather than a document either party signed at the time, and it should be weighted accordingly: strong evidence of identity, but not chain-verifiable in the way the transaction's inputs and outputs are.

• What does the ledger itself prove about a transaction, independent of who later claims to have sent or received it?
• How is a change output distinguished from a payment output in any given transaction?
• What weight should a participant's later recollection carry against contemporaneous but anonymous chain data?

Block 170 is a clean illustration of the unspent-output model precisely because so little else about it is disputed: the mechanism is chain-verifiable, and only the identity layered on top depends on someone's word.