TYPE 0x0502 · ANCHOR FAMILY

ANCHOR_CHANNEL

Lightning channel anchor. Verifies local and remote channel pubkeys alongside a commitment number. Used to anchor Lightning channel state on-chain for backup and verification purposes.

Anchor Invertible

Ladder Diagram

Fields

Field	Data Type	Size	Side	Description
commitment_number	NUMERIC	1-4 B	Conditions	Channel commitment number (must be > 0)

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

No witness fields required. The commitment number is committed in conditions.

Wire Format Breakdown

0x0502 0 3 PUBKEY · 33B PUBKEY · 33B NUMERIC · 3B Conditions = 78 bytes

0x0502 0 0 Witness = 4 bytes (empty block)

Total 82 bytes

Evaluation Logic

1.Extract PUBKEY fields (verified via Merkle leaf). Need exactly 2 channel keys.

2.If fewer than 2 pubkeys → ERROR

3.Read commitment_number from NUMERIC field

4.If commitment_number ≤ 0 → UNSATISFIED

5.Otherwise → SATISFIED

Return Values

Condition	Result
Fewer than 2 pubkey fields	ERROR
Missing NUMERIC field	ERROR
commitment_number ≤ 0	UNSATISFIED
2 pubkeys + commitment_number > 0	SATISFIED

JSON Wire Format

Conditions (channel state anchor)

{
  "type": "ANCHOR_CHANNEL",
  "inverted": false,
  "fields": [
    { "type": "PUBKEY", "hex": "02a1b2c3...local channel key...33 bytes" },
    { "type": "PUBKEY", "hex": "03d4e5f6...remote channel key...33 bytes" },
    { "type": "NUMERIC", "value": 42 }
  ]
}

Anchors commitment #42 of a Lightning channel identified by the local and remote pubkeys.

Use Cases

Lightning Channel State Anchoring

Commit the current channel state on-chain, creating a verifiable record of the commitment number and both channel keys. Enables trustless channel state auditing without closing the channel.

Channel Backup Verification

Anchor channel parameters on-chain as a backup reference. If local state is lost, the anchored data can be used to verify the correct channel keys and latest known commitment number.

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