Signature Templates

When a contract function has a sig parameter, it needs a cryptographic signature from a private key for the spending transaction. In place of a signature, a SignatureTemplate can be passed, which will generate the correct signature when the transaction is built.

Tip: SignatureTemplate can be used with a Contract as a function argument to generate a signature automatically, or can be used in the TransactionBuilder to create an Unlocker for a P2PKH UTXO.

SignatureTemplate

Constructor

from cashscript_py import SignatureTemplate

alice_signature_template = SignatureTemplate(
    "L4vmKsStbQaCvaKPnCzdRArZgdAxTqVx8vjMGLW5nHtWdRguiRi1"
)

The signer can be:

WIF string
32-byte secret key (bytes)
hex string (with or without 0x prefix)

Example

from cashscript_py import Output, TransactionBuilder

transfer_details = await (
    TransactionBuilder(provider)
    .add_input(selected_contract_utxo, contract.unlock["transfer"](alice_signature_template))
    .add_output(Output(to="bitcoincash:qrhea03074073ff3zv9whh0nggxc7k03ssh8jv9mkx", amount=10_000))
    .send()
)

The hashtype and signature_algorithm options are covered under Advanced usage.

SignatureTemplate methods

unlock_p2pkh()

Importantly, SignatureTemplate can also be used to generate the Unlocker for a P2PKH UTXO:

signature_template.unlock_p2pkh() -> Unlocker

Example

alice_utxos = await provider.get_utxos(alice_address)
transaction_builder.add_input(alice_utxos[0], alice_template.unlock_p2pkh())

get_public_key()

signature_template.get_public_key() -> bytes

Get the matching compressed public key (33 bytes).

Example

alice_public_key = alice_template.get_public_key()

sign_message_hash()

signature_template.sign_message_hash(message_hash_32: bytes) -> bytes

Sign a 32-byte message hash (not a transaction preimage). This is useful for generating signatures for datasig use cases.

Example

import hashlib

message_hash_32: bytes = hashlib.sha256(bytes.fromhex("00" * 32)).digest()
signature: bytes = alice_template.sign_message_hash(message_hash_32)

Advanced usage

HashType

The default hashtype is HashType.SIGHASH_ALL | HashType.SIGHASH_UTXOS because this is typically the most secure option for smart contract use cases.

Available flags (from the CashScript-Py implementation):

class HashType(Flag):
    SIGHASH_ALL = 0x01
    SIGHASH_NONE = 0x02
    SIGHASH_SINGLE = 0x03
    SIGHASH_UTXOS = 0x20
    SIGHASH_FORKID = 0x40
    SIGHASH_ANYONECANPAY = 0x80

Example

from cashscript_py import HashType, SignatureTemplate

signature_template = SignatureTemplate(
    wif,
    hashtype=HashType.SIGHASH_ALL | HashType.SIGHASH_UTXOS,
)
configured_hash_type = signature_template.get_hash_type()

SignatureAlgorithm

The signature_algorithm parameter determines which cryptographic algorithm is used for signing. By default, the modern and compact Schnorr algorithm is used.

Available flags (from the CashScript-Py implementation):

class SignatureAlgorithm(Flag):
    ECDSA = 0x00
    SCHNORR = 0x01

Example

from cashscript_py import HashType, SignatureAlgorithm, SignatureTemplate

signature_template = SignatureTemplate(
    wif,
    signature_algorithm=SignatureAlgorithm.SCHNORR,
)
configured_signature_algorithm = signature_template.get_signature_algorithm()

Notes on contract `sig` arguments

CashScript-Py accepts a SignatureTemplate as a function argument for sig parameters. The Contract will:

build the signature hash for the input being signed, and
ask the template to generate the correct signature at build time.

This allows you to pass SignatureTemplate(...) in place of a raw signature.

Signature Templates