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. While the serialized versions of these structs are used in the bridge’s API, they are parsed by the chain into a more convenient internal representation. See Data Model.

Block Headers

The 80 bytes block header encodes the following information:

Note

as per bip64, blocks with a version number of less than 4 are rejected. As a consequence, blocks that were mined before December 2015 will not successfully parse in the bridge. This is acceptable, because the bridge is not expected to be initialized with such an old block as genesis.

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	timestamp	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. Both ‘normal’ transaction and transactions segregated witness data are supported.

Bytes	Parameter	Type	Description
4	version	i32	Transaction version number.
0/2	flags	Option<u8[2]>	If present, always 0001, and indicates the presence of witness data
var	tx_in count	uint	Number of transaction inputs.
var	tx_in	Inputs	List of transaction inputs.
var	tx_out count	uint	The number of transaction outputs.
var	tx_out	Outputs	List of transaction outputs.
var	tx_witnesses	Witness	A list of witnesses, one for each input; omitted if flag is omitted above.
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.

Witness

Bytes	Parameter	Type	Description
var	count	uint	The number of witness stack items in this tx_witness.
var	witness_stack	Witness Stack Item	List of witness stack items making up this tx_witness.

Witness Stack Item

Bytes	Parameter	Type	Description
var	count	uint	The number of bytes in this witness stack item.
var	witness_stack	u8[]	The bytes making up the witness stack item.