Bitcoin Data Model

This is a high-level overview of Bitcoin’s data model. For the full details, refer to https://bitcoin.org/en/developer-reference.

Block Headers

The 80 bytes block header hash encodes the following information:

Bytes	Parameter	Type	Description
4	version	i32	The block version to follow.
32	hashPrevBlock	char[32]	The double sha256 hash of the previous block header.
32	merkleRoot	char[32]	The double sha256 hash of the Merkle root of all transaction hashes in this block.
4	time	u32	The block timestamp included by the miner.
4	nBits	u32	The target difficulty threshold, see also the Bitcoin documentation.
4	nonce	u32	The nonce chosen by the miner to meet the target difficulty threshold.

Transactions

A transaction is broadcasted in a serialized byte format (also called raw format). It consists of a variable size of bytes and has the following format.

Bytes	Parameter	Type	Description
4	version	i32	Transaction version number.
var	tx_in count	uint	Number of transaction inputs.
var	tx_in	txIn	Transaction inputs.
var	tx_out count	uint	The number of transaction outputs.
var	tx_out	txOut	Transaction outputs.
4	lock_time	u32	A Unix timestamp OR block number.

Note

Bitcoin uses the term “CompactSize Unsigned Integers” to refer to variable-length integers, which are used to indicate the number of bytes representing transaction inputs and outputs. See the Developer Reference for more details.

Inputs

Bitcoin’s UTXO model requires a new transaction to spend at least one existing and unspent transaction output as a transaction input. The txIn type consists of the following bytes. See the reference for further details.

Bytes	Parameter	Type	Description
36	previous_output	outpoint	The output to be spent consisting of the transaction hash (32 bytes) and the output index (4 bytes).
var	script bytes	uint	Number of bytes in the signature script (max 10,000 bytes).
var	signature script	char[]	The script satisfying the output’s script.
4	sequence	u32	Sequence number (default 0xffffffff).

Outputs

The transaction output has the following format according to the reference.

Bytes	Parameter	Type	Description
8	value	i64	Number of satoshis to be spent.
1+	pk_script bytes	uint	Number of bytes in the script.
var	pk_script	char[]	Spending condition as script.