RGB++

Bitcoin Layer 2 Protocol

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OP_RETURN

Bitcoin script opcode for embedding arbitrary data in transactions.

OP_RETURNBitcoin

The OP_RETURN standard locking script just contains the OP_RETURN opcode followed by one or more data pushes. The standard OP_RETURN script has a maximum size limit of 83 bytes. However, there is an ongoing discussion and corresponding pull request to relax these standardness restrictions.

Key Characteristics

Data Embedding

Allows embedding arbitrary data directly in Bitcoin transactions

Provably Unspendable

Creates outputs that can never be spent, reducing UTXO set size

Size Limit

Standard limit of 83 bytes for data payload

Standard Script

Recognized as a standard transaction type by Bitcoin nodes

Script Structure

Example OP_RETURN Script

OP_RETURN
OP_PUSHBYTES_11
68656c6c6f20776f726c64

This example embeds "hello world" (in hexadecimal) into the Bitcoin blockchain.

Use Cases

Timestamping

Prove the existence of documents or data at a specific time

Asset Protocols

Embed metadata for colored coins and other asset protocols

Commitment Schemes

Store hash commitments for off-chain protocols

Protocol Signaling

Signal protocol upgrades or network parameters

Role in RGB++

OP_RETURN outputs may be used in RGB++ transactions to embed commitment data or protocol identifiers that link Bitcoin transactions to their corresponding CKB Cell operations. This enables the binding mechanism to work by providing verifiable on-chain commitments.

Advantages & Considerations

Advantages

  • • Permanent data storage
  • • Standard transaction type
  • • Provably unspendable
  • • Widely supported

Considerations

  • • Limited data size (83 bytes)
  • • Increases blockchain size
  • • Transaction fees apply
  • • Not suitable for large data

Recent Developments

There are ongoing discussions in the Bitcoin community about relaxing the 83-byte size limit for OP_RETURN outputs. Bitcoin Core Pull Request #32359 proposes changes to these standardness restrictions.

These changes could potentially allow for larger data payloads in OP_RETURN outputs, which would benefit protocols like RGB++ that need to embed commitment data.

External Resources