psbt: enforce required locktime bounds
What the developer wrote
Authored by Sjors Provoost
psbt: enforce required locktime bounds
What changed, and why it matters
This change makes the hardware-wallet interface library stricter when reading PSBT (Partially Signed Bitcoin Transaction) files. It now rejects locktime values that don't follow Bitcoin's rules: a time-based locktime must be at least 500,000,000, and a block-height-based locktime must be greater than 0 and less than 500,000,000. Without these checks, a malformed or malicious PSBT could confuse a hardware wallet about when a transaction is allowed to be mined, potentially leading to signing something the user didn't expect.
Review whether any other PSBT implementations or downstream hardware-wallet clients need the same locktime-bound validation, and ensure the new test vectors are exercised in CI. Consider adding explicit documentation or release-note mention of the stricter parsing.
Security signals we found
Input validation added to PSBT deserialization
Enforcement of Bitcoin locktime semantics boundary (500000000)
New negative test cases for invalid locktime combinations
Potential for PSBT parsing confusion / unexpected signing behavior before patch
Evidence from the diff
The patch adds validation in hwilib/psbt.py’s PartiallySignedInput.deserialize() for the BIP371 PSBT_IN_REQUIRED_TIME_LOCKTIME and PSBT_IN_REQUIRED_HEIGHT_LOCKTIME fields. It enforces the Bitcoin consensus convention that nLockTime < 500000000 is interpreted as a block height and >= 500000000 as a Unix timestamp, so the two PSBT fields must not overlap. Previously the library decoded the 4-byte little-endian values without range checks. New negative test vectors were added to test/data/test_psbt.json.
Changed components
hwilib/psbt.pyPartiallySignedInput.deserialize()PSBT_IN_REQUIRED_TIME_LOCKTIME handlingPSBT_IN_REQUIRED_HEIGHT_LOCKTIME handlingInspect captured patch +8 / −1
### hwilib/psbt.py
@@ -290,6 +290,8 @@ def deserialize(self, f: Readable) -> None:
if len(v) != 4:
raise PSBTSerializationError("Input time based locktime is not 4 bytes")
self.time_locktime = struct.unpack("<I", v)[0]
+ if self.time_locktime < 500000000:
+ raise PSBTSerializationError("Input time based locktime is less than 500000000")
elif key_type == PartiallySignedInput.PSBT_IN_REQUIRED_HEIGHT_LOCKTIME:
if self.version == 0:
raise PSBTSerializationError("PSBT_IN_REQUIRED_HEIGHT_LOCKTIME is not allowed in PSBTv0")
@@ -301,6 +303,8 @@ def deserialize(self, f: Readable) -> None:
if len(v) != 4:
raise PSBTSerializationError("Input height based locktime is not 4 bytes")
self.height_locktime = struct.unpack("<I", v)[0]
+ if self.height_locktime == 0 or self.height_locktime >= 500000000:
+ raise PSBTSerializationError("Input height based locktime is not greater than 0 and less than 500000000")
elif key_type == PartiallySignedInput.PSBT_IN_TAP_KEY_SIG:
if key in key_lookup:
raise PSBTSerializationError("Duplicate key, input Taproot key signature already provided")
### test/data/test_psbt.json
@@ -47,7 +47,10 @@
"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",
"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",
"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",
- "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"
+ "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",
+ "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",
+ "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",
+ "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"
]
,
"valid" : [Why this scored 47/100
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