TYPE 0x0903 · LEGACY FAMILY

P2SH_LEGACY

Legacy P2SH (pay-to-script-hash) wrapped as a typed Ladder Script block. Inner script must be valid Ladder Script conditions — no arbitrary bytes allowed. Closes the P2SH data-embedding surface.

Legacy Invertible

Ladder Diagram

Fields

Field	Data Type	Size	Side	Description
hash160	HASH160	20 B	Conditions	RIPEMD160(SHA256(preimage)) commitment to the inner script. Node-computed — the user provides PREIMAGE (serialised Ladder Script conditions) and the node computes this field automatically. Raw hash input is rejected.
preimage	PREIMAGE	var	Witness	Serialised Ladder Script conditions (the inner script) — provided by the user. The node derives HASH160 from this data at creation time.
[inner witness]	var	var	Witness	Witness fields required to satisfy the inner conditions

Wire Format Breakdown

Conditions side (in scriptPubKey):

0x0903 0 1 HASH160 · 20B = 26 bytes

Witness side (in input witness):

0x0903 0 n PREIMAGE · varB [inner witness fields] = variable

Total (conditions + witness) variable

Witness size depends on the inner Ladder Script conditions and their witness fields.

Evaluation Logic

1. Compute HASH160(PREIMAGE) = RIPEMD160(SHA256(PREIMAGE)).

2. Compare computed hash to committed HASH160. If mismatch → UNSATISFIED

3. Deserialize PREIMAGE as Ladder Script conditions. If invalid → UNSATISFIED

4. Evaluate inner conditions with remaining witness fields. Result → SATISFIED or UNSATISFIED

Return Values

Condition	Result
Missing HASH160 or PREIMAGE	ERROR
HASH160 wrong size (not 20B)	ERROR
HASH160(PREIMAGE) != committed hash	UNSATISFIED
PREIMAGE fails to deserialize as Ladder conditions	ERROR
Inner conditions evaluation fails	UNSATISFIED
Recursion depth > 2	ERROR
Inner conditions satisfied	SATISFIED

JSON Wire Format

Conditions (scriptPubKey)

{
  "type": "P2SH_LEGACY",
  "inverted": false,
  "fields": [
    { "type": "HASH160", "hex": "89abcd...20 bytes" }
  ]
}

Witness (input)

{
  "type": "P2SH_LEGACY",
  "inverted": false,
  "fields": [
    { "type": "PREIMAGE", "hex": "01020304...serialised Ladder conditions" },
    { "type": "PUBKEY", "hex": "02abc1...33 bytes" },
    { "type": "SIGNATURE", "hex": "e5f6a7...64 bytes" }
  ]
}

Notes

Inner conditions must deserialize as valid Ladder Script — arbitrary bytes are rejected.
The HASH160 field is node-computed: the user supplies PREIMAGE (the inner script) and the node derives the hash commitment automatically. Submitting a raw HASH160 value directly is rejected.
Recursion depth limited to 2 to prevent unbounded nesting.
Prevents the arbitrary data embedding that plagues Bitcoin P2SH.
The inner script is only revealed at spend time, preserving script privacy until then.

Use Cases

Anti-Spam Script Wrapping

Wraps legacy P2SH but requires inner script to be valid Ladder conditions. No arbitrary data.

Nested Conditions

Inner Ladder conditions can contain any block type, enabling complex spending policies behind a hash commitment.

← P2PKH_LEGACY P2WPKH_LEGACY →