TYPE 0x0103 · TIMELOCK FAMILY

CLTV

Absolute timelock in blocks (BIP 65). Transaction cannot be included until block height reaches the specified value.

Timelock Invertible

Ladder Diagram

Fields

Field	Data Type	Size	Side	Description
locktime	NUMERIC	1-4 B	Conditions	Absolute block height. BIP 65's height/time switch (LOCKTIME_THRESHOLD = 500000000) lives inside `CheckLockTime` — for CLTV, encode a value < 500000000.

No witness fields required — evaluation uses the current block height from the evaluation context.

Wire Format Breakdown

0x0103 0 1 NUMERIC · 3B Conditions = 4 + 5 = 9 bytes

0x0103 0 0 Witness = 4 bytes (empty block)

Total 15 bytes

Evaluation Logic

1.Read the conditions NUMERIC field as an int64 locktime_val. If absent or undecodable → ERROR

2.Range check: if locktime_val < 0 or locktime_val > 0xFFFFFFFF → UNSATISFIED (guards the narrowing cast to uint32_t).

3.Call sig_checker.CheckLockTime(uint32_t(locktime_val)); this delegates to BIP 65 semantics (height vs MTP discriminated by </≥ LOCKTIME_THRESHOLD). Fails → UNSATISFIED; passes → SATISFIED

Return Values

Condition	Result
NUMERIC field missing or undecodable	ERROR
`locktime_val` negative or > 0xFFFFFFFF (uint32 range guard)	UNSATISFIED
`CheckLockTime` fails (block height < locktime, or input nSequence is final)	UNSATISFIED
`CheckLockTime` passes (block height ≥ locktime)	SATISFIED

JSON Wire Format

Conditions (locked until block 850000)

{
  "type": "CLTV",
  "inverted": false,
  "fields": [
    { "type": "NUMERIC", "value": 850000 }
  ]
}

This locks the UTXO until block 850,000 is reached. Any transaction attempting to spend it before that height will be rejected by consensus.

Worked Example

locktime = 850000

Block 849999: 849999 < 850000 → UNSATISFIED

Block 850000: 850000 ≥ 850000 → SATISFIED

Block 900000: 900000 ≥ 850000 → SATISFIED

Use Cases

Future-Dated Payments

Funds locked until a future block height, creating a hard floor on when they can move. The recipient can see the payment on-chain but cannot spend it until the specified height is reached.

Vesting Schedules

Token grants that unlock at specific block heights, ensuring milestone-based disbursement without requiring a trusted intermediary. Each tranche is a separate UTXO with its own CLTV value.

Time-Locked Escrow

Escrow outputs that cannot be released before a specific block height, giving both parties a deterministic settlement window anchored to consensus rather than wall-clock time.

← CSV_TIME CLTV_TIME →