BitcoinTx

BitcoinTx

Allows to reference Bitcoin raw transaction in Solidity.

See https://developer.bitcoin.org/reference/transactions.html#raw-transaction-format

Raw Bitcoin transaction data:

Bytes	Name	BTC type	Description
4	version	int32_t (LE)	TX version number
varies	tx_in_count	compactSize uint (LE)	Number of TX inputs
varies	tx_in	txIn[]	TX inputs
varies	tx_out_count	compactSize uint (LE)	Number of TX outputs
varies	tx_out	txOut[]	TX outputs
4	lock_time	uint32_t (LE)	Unix time or block number

Non-coinbase transaction input (txIn):

Bytes	Name	BTC type	Description
36	previous_output	outpoint	The previous outpoint being spent
varies	script_bytes	compactSize uint (LE)	The number of bytes in the signature script
varies	signature_script	char[]	The signature script, empty for P2WSH
4	sequence	uint32_t (LE)	Sequence number

The reference to transaction being spent (outpoint):

Bytes	Name	BTC type	Description
32	hash	char[32]	Hash of the transaction to spend
4	index	uint32_t (LE)	Index of the specific output from the TX

Transaction output (txOut):

Bytes	Name	BTC type	Description
8	value	int64_t (LE)	Number of satoshis to spend
1+	pk_script_bytes	compactSize uint (LE)	Number of bytes in the pubkey script
varies	pk_script	char[]	Pubkey script

compactSize uint format:

Value	Bytes	Format
>= 0 && <= 252	1	uint8_t
>= 253 && <= 0xffff	3	0xfd followed by the number as uint16_t (LE)
>= 0x10000 && <= 0xffffffff	5	0xfe followed by the number as uint32_t (LE)
>= 0x100000000 && <= 0xffffffffffffffff	9	0xff followed by the number as uint64_t (LE)

(*) compactSize uint is often references as VarInt)

Coinbase transaction input (txIn):

Bytes	Name	BTC type	Description
32	hash	char[32]	A 32-byte 0x0 null (no previous_outpoint)
4	index	uint32_t (LE)	0xffffffff (no previous_outpoint)
varies	script_bytes	compactSize uint (LE)	The number of bytes in the coinbase script
varies	height	char[]	The block height of this block (BIP34) (*)
varies	coinbase_script	none	Arbitrary data, max 100 bytes
4	sequence	uint32_t (LE)	Sequence number

(*) Uses script language: starts with a data-pushing opcode that indicates how many bytes to push to the stack followed by the block height as a little-endian unsigned integer. This script must be as short as possible, otherwise it may be rejected. The data-pushing opcode will be 0x03 and the total size four bytes until block 16,777,216 about 300 years from now.

Info

struct Info {
  bytes4 version;
  bytes inputVector;
  bytes outputVector;
  bytes4 locktime;
}

Proof

struct Proof {
  bytes merkleProof;
  uint256 txIndexInBlock;
  bytes bitcoinHeaders;
}

UTXO

struct UTXO {
  bytes32 txHash;
  uint32 txOutputIndex;
  uint64 txOutputValue;
}

RSVSignature

struct RSVSignature {
  bytes32 r;
  bytes32 s;
  uint8 v;
}

validateProof

function validateProof(struct BridgeState.Storage self, struct BitcoinTx.Info txInfo, struct BitcoinTx.Proof proof) internal view returns (bytes32 txHash)

Validates the SPV proof of the Bitcoin transaction. Reverts in case the validation or proof verification fail.

Parameters

Name	Type	Description
self	struct BridgeState.Storage
txInfo	struct BitcoinTx.Info	Bitcoin transaction data.
proof	struct BitcoinTx.Proof	Bitcoin proof data.

Return Values

Name	Type	Description
txHash	bytes32	Proven 32-byte transaction hash.

evaluateProofDifficulty

function evaluateProofDifficulty(struct BridgeState.Storage self, bytes bitcoinHeaders) internal view

Evaluates the given Bitcoin proof difficulty against the actual Bitcoin chain difficulty provided by the relay oracle. Reverts in case the evaluation fails.

Parameters

Name	Type	Description
self	struct BridgeState.Storage
bitcoinHeaders	bytes	Bitcoin headers chain being part of the SPV proof. Used to extract the observed proof difficulty.

extractPubKeyHash

function extractPubKeyHash(struct BridgeState.Storage, bytes output) internal pure returns (bytes20 pubKeyHash)

Extracts public key hash from the provided P2PKH or P2WPKH output. Reverts if the validation fails.

Requirements:

• The output must be of P2PKH or P2WPKH type and lock the funds on a 20-byte public key hash.

Parameters

Name	Type	Description
	struct BridgeState.Storage
output	bytes	The transaction output.

Return Values

Name	Type	Description
pubKeyHash	bytes20	20-byte public key hash the output locks funds on.

makeP2PKHScript

function makeP2PKHScript(bytes20 pubKeyHash) internal pure returns (bytes26)

Build the P2PKH script from the given public key hash.

The P2PKH script has the following byte format: <0x1976a914> <20-byte PKH> <0x88ac>. According to https://en.bitcoin.it/wiki/Script#Opcodes this translates to:

• 0x19: Byte length of the entire script

• 0x76: OP_DUP

• 0xa9: OP_HASH160

• 0x14: Byte length of the public key hash

• 0x88: OP_EQUALVERIFY

• 0xac: OP_CHECKSIG which matches the P2PKH structure as per: https://en.bitcoin.it/wiki/Transaction#Pay-to-PubkeyHash

Parameters

Name	Type	Description
pubKeyHash	bytes20	The 20-byte public key hash.

Return Values

Name	Type	Description
[0]	bytes26	The P2PKH script.

makeP2WPKHScript

function makeP2WPKHScript(bytes20 pubKeyHash) internal pure returns (bytes23)

Build the P2WPKH script from the given public key hash.

The P2WPKH script has the following format: <0x160014> <20-byte PKH>. According to https://en.bitcoin.it/wiki/Script#Opcodes this translates to:

• 0x16: Byte length of the entire script

• 0x00: OP_0

• 0x14: Byte length of the public key hash which matches the P2WPKH structure as per: https://github.com/bitcoin/bips/blob/master/bip-0141.mediawiki#P2WPKH

Parameters

Name	Type	Description
pubKeyHash	bytes20	The 20-byte public key hash.

Return Values

Name	Type	Description
[0]	bytes23	The P2WPKH script.