Single-Use Seals and UTXOs
Single-use seals are the heart of the RGB protocol. They provide a standardized way to represent and transfer ownership of off-chain assets using the Bitcoin UTXO model.
The Piggy Bank Analogy
- A Bitcoin UTXO (Unspent Transaction Output) can be thought of as a piggy bank or a sealed box.
- To spend the Bitcoin, you must destroy (spend) the UTXO.
- In RGB, we assign assets to these UTXOs. To move the asset, you must spend the underlying UTXO.
- Since a UTXO can only be spent once, it acts as a “single-use seal.” Once broken, the asset must be reassigned to a new UTXO (seal).
How it Works in Practice
- Issuance: An issuer creates a contract and assigns the initial supply of tokens to a set of Bitcoin UTXOs.
- Transfer: The owner of the UTXO creates an “Ownership Transfer” message. This message specifies the new UTXOs that will now “own” the assets.
- Commitment: The hash of this transfer message is committed inside a Bitcoin transaction that spends the original UTXO.
- Verification: The receiver checks the Bitcoin blockchain to ensure the transaction spending the original UTXO was confirmed. This guarantees that the “seal” was used and the assets were moving.
Benefits
- Double-Spending Prevention: By tethering the asset to a UTXO, RGB inherits the double-spending protection of the Bitcoin network.
- Modular Ownership: Assets can be assigned to any UTXO, even those controlled by complex scripts like multi-sigs or time-locks.
- Efficiency: The assets and Bitcoins move in the same “box,” but they don’t have to share the same destiny; you can move the assets while keeping the satoshis, or vice versa (though practically you move them together by spending the UTXO).