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Add PSBT_IN_TAP_KEY_SIG field to PSBTs #68

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Add PSBT_IN_TAP_KEY_SIG field to PSBTs #68

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e5beacc
tap_key_sig
pythcoiner Dec 21, 2024
638a824
taproot_key_sig serialization adjust
odudex Dec 21, 2024
ef61cca
Add PSBT_IN_TAP_KEY_SIG parsing to the InputScope read_value function
odudex Jan 30, 2025
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25 changes: 20 additions & 5 deletions src/embit/psbt.py
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Original file line number Diff line number Diff line change
Expand Up @@ -142,6 +142,7 @@ def __init__(self, unknown: dict = {}, vin=None, compress=CompressMode.KEEP_ALL)
self.taproot_bip32_derivations = OrderedDict()
self.taproot_internal_key = None
self.taproot_merkle_root = None
self.taproot_key_sig = None
self.taproot_sigs = OrderedDict()
self.taproot_scripts = OrderedDict()

Expand Down Expand Up @@ -187,6 +188,7 @@ def update(self, other):
self.taproot_bip32_derivations.update(other.taproot_bip32_derivations)
self.taproot_internal_key = other.taproot_internal_key
self.taproot_merkle_root = other.taproot_merkle_root or self.taproot_merkle_root
self.taproot_key_sig = other.taproot_key_sig or self.taproot_key_sig
self.taproot_sigs.update(other.taproot_sigs)
self.taproot_scripts.update(other.taproot_scripts)
self.final_scriptsig = other.final_scriptsig or self.final_scriptsig
Expand Down Expand Up @@ -350,7 +352,15 @@ def read_value(self, stream, k):
elif k == b"\x10":
self.sequence = int.from_bytes(v, "little")

# TODO: 0x13 - tap key signature
# PSBT_IN_TAP_KEY_SIG
elif k[0] == 0x13:
# read the taproot key sig
if len(k) != 1:
raise PSBTError("Invalid taproot key signature key")
if self.taproot_key_sig is not None:
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@pythcoiner pythcoiner Feb 3, 2025

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in which case this can happen?
maybe we can avoid error here if self.taproot_key_sig == v in this case anyways?

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@odudex odudex Feb 3, 2025

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I'm not exactly sure in what context this function is called, as iirc we neither use it directly in Krux nor indirectly. I simply replicated the verification from final scriptsig and final script witness, believing it is a sanity check.

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@pythcoiner pythcoiner Feb 7, 2025

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Anyway, I guess if we sign twice an input, it shold be with 2 differents nonces? (so we should end up with a different signature)

raise PSBTError("Duplicated taproot key signature")
self.taproot_key_sig = v

# PSBT_IN_TAP_SCRIPT_SIG
elif k[0] == 0x14:
if len(k) != 65:
Expand Down Expand Up @@ -434,6 +444,11 @@ def write_to(self, stream, skip_separator=False, version=None, **kwargs) -> int:
r += ser_string(stream, b"\x10")
r += ser_string(stream, self.sequence.to_bytes(4, "little"))

# PSBT_IN_TAP_KEY_SIG
if self.taproot_key_sig is not None:
r += ser_string(stream, b"\x13")
r += ser_string(stream, self.taproot_key_sig)

# PSBT_IN_TAP_SCRIPT_SIG
for pub, leaf in self.taproot_sigs:
r += ser_string(stream, b"\x14" + pub.xonly() + leaf)
Expand Down Expand Up @@ -881,11 +896,11 @@ def sign_input_with_tapkey(
sighash=sighash,
)
sig = pk.schnorr_sign(h)
wit = sig.serialize()
sigdata = sig.serialize()
if sighash != SIGHASH.DEFAULT:
wit += bytes([sighash])
# TODO: maybe better to put into internal key sig field
inp.final_scriptwitness = Witness([wit])
sigdata += bytes([sighash])
inp.taproot_key_sig = sigdata
inp.final_scriptwitness = Witness([sigdata])
# no need to sign anything else
return 1
counter = 0
Expand Down