TYPE 0x0003 · SIGNATURE FAMILY

ADAPTOR_SIG

Adaptor signature verification. Requires a signing key, an adaptor point, and an adapted signature. Enables scriptless scripts and atomic protocols without hash locks.

Signature Non-Invertible

Ladder Diagram

Fields

Field	Data Type	Size	Side	Description
signing_key	PUBKEY	32-33 B	Witness	Signing public key (x-only 32B or compressed 33B). The adaptor point is NOT revealed in the witness — the adaptor secret is applied off-chain to produce the adapted signature.
signature	SIGNATURE	64-65 B	Witness	Adapted Schnorr signature (the completed adaptor signature)

Both public keys folded into Merkle leaf via merkle_pub_key (PubkeyCountForBlock = 2). No key fields in conditions.

Wire Format Breakdown

Conditions side (in scriptPubKey):

0x0003 0 2 COMMIT (key) · 32B COMMIT (adaptor) · 32B = 72 bytes

Witness side (in input witness):

0x0003 0 2 KEY · 32B SIGNATURE · 64B = 104 bytes

Total (conditions + witness) 178 bytes

Minimal case with x-only keys and 64-byte Schnorr adapted signature.

Evaluation Logic

1. Verify both witness pubkeys (signing_key and adaptor_point) against Merkle leaf (merkle_pub_key). If either mismatches → UNSATISFIED

2. Verify adaptor_point is a valid 32-byte x-only point on the curve. If invalid → UNSATISFIED

3. Verify adapted SIGNATURE against signing_key with adaptor_point. If invalid → UNSATISFIED

4. Adapted signature valid → SATISFIED

Return Values

Condition	Result
Missing PUBKEY or SIGNATURE in witness	ERROR
Fewer than 2 pubkeys in Merkle leaf (PubkeyCountForBlock = 2)	ERROR
Adaptor point not valid x-only point	ERROR
Signing key commitment mismatch	UNSATISFIED
Adaptor point commitment mismatch	UNSATISFIED
Adapted signature verification fails	UNSATISFIED
Adapted signature valid	SATISFIED

JSON Wire Format

Conditions (scriptPubKey)

{
  "type": "ADAPTOR_SIG",
  "inverted": false,
  "fields": [
    { "type": "PUBKEY", "hex": "02abc1...33 bytes (signing key)" },
    { "type": "PUBKEY", "hex": "03def2...33 bytes (adaptor point)" }
  ]
}

Witness (input)

{
  "type": "ADAPTOR_SIG",
  "inverted": false,
  "fields": [
    { "type": "PUBKEY", "hex": "02abc1...33 bytes (signing key)" },
    { "type": "SIGNATURE", "hex": "e5f71b...64 bytes (adapted)" }
  ]
}

Use Cases

DLC Oracle Contracts

Discreet Log Contracts use adaptor signatures to bind payouts to oracle attestations. The oracle's adaptor point commits to a future event outcome. When the oracle signs the outcome, the adapted signature becomes completable, enabling trustless settlement.

Scriptless Scripts

Adaptor signatures enable conditional payments without revealing any script on-chain. The spending transaction looks like a normal single-sig spend, but the act of completing the adaptor reveals a secret scalar to the counterparty.

Atomic Swaps Without Hash Locks

Cross-chain atomic swaps using adaptor signatures instead of HTLCs. Both parties create adaptor signatures with the same adaptor point. Completing one swap leg reveals the adaptor secret, enabling the other leg. More private than hash-lock swaps.

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