RGB++ Layer: The Hub of BTCFi and the UTXO World

In July 2024, CKB officially launched the RGB++ Layer project, marking the transition of the previously released RGB++ protocol from theory to practice, and will introduce more specific application scenarios. The RGB++ Layer, with its vision of building a BTCFi ecosystem between BTC and CKB, Cardano, and other UTXO public chains, quickly became the focus of attention in the industry.

RGB++ Layer is based on the RGB++ protocol and utilizes homomorphic binding and Leap technology to provide a "no cross-chain bridge" full-chain interaction experience for RGB++ native assets or inscriptions/runes across UTXO-based public chains such as BTC, CKB, and Cardano. It leverages CKB's Turing-complete smart contract environment to build infrastructure for Bitcoin, ranging from asset issuance to complex DeFi functionalities.

Due to the RGB++ Layer's backing by the complete account abstraction ecosystem of CKB, it is compatible with Bitcoin accounts and wallets, providing a good experience for Bitcoin users and paving the way for the large-scale application of BTCFi.

RGB++ Protocol: The Theoretical Foundation of RGB++ Layer

The RGB++ protocol was released in January this year, with its core concept being to replace the "client-side validation" of the RGB protocol with on-chain validation via the CKB blockchain. Essentially, it uses CKB as a decentralized indexer to complete tasks such as data storage and asset source verification, acting as the validation layer and DA layer for the RGB protocol, in order to address the shortcomings of the RGB protocol in user experience and support for DeFi.

RGB++ introduces the concept of isomorphic bindings, using Cells on the CKB chain as the data carrier for inscription/runic assets, and establishing binding relationships between Cells and UTXOs on the Bitcoin/Cardano/Liquid chains, allowing RGB++ assets to inherit the security of these UTXO public chains and prevent double spending.

For example, if Alice wants to transfer some TEST tokens to Bob, she can generate a statement that binds a Cell storing the TEST asset information to Bob's Bitcoin UTXO. If Bob then transfers the TEST tokens, the bound Bitcoin UTXO must also be transferred accordingly.

Isomorphic Binding and Leap: Asset Issuance of BTCFi and Bridge-less Cross-chain Layer

Isomorphic binding and Leap are the two core features of the RGB++ Layer. To understand these two concepts, one must first understand the CKB Cell model.

Cell is an extended UTXO of CKB, containing fields such as LockScript, TypeScript, and Data. LockScript is similar to Bitcoin's locking script, used for permission verification; TypeScript is akin to smart contract code; Data is used to store asset data.

When issuing RGB++ assets on CKB, it is necessary to create a Cell and fill in the relevant fields. Since the Cell structure is similar to Bitcoin's UTXO structure and CKB is compatible with Bitcoin's signature algorithm, users can operate CKB chain assets using a Bitcoin wallet.

The core of isomorphism binding allows for rewriting RGB++ asset data on the CKB chain using accounts from different public chains such as BTC and Cardano. Leap is based on isomorphism binding, performing "rebinding" of the UTXO bound to RGB++ assets, such as rebinding from Bitcoin UTXO to Cardano UTXO, achieving the transfer of asset control rights between different accounts.

Implementation Method of Isomorphic Binding

For example, Alice transfers 40 TEST tokens to Bob:

1. Alice constructs the CKB transaction data locally, specifying to destroy Cell#0,生成Cell#1 for Bob, and leaves Cell#2 for herself.

2. Alice generates a statement, including Cell#1绑定到BTC UTXO#1, Cell#2绑定到BTC UTXO#2.

3. Alice generates a Commitment, containing the above declaration and CKB transaction data.

4. Alice initiates a transaction on the Bitcoin chain, destroying UTXO#0,生成UTXO#1 to Bob, leaving UTXO#2 for herself, and writes the Commitment on the chain.

5. Finally, send the CKB transaction to the CKB chain.

Throughout the process, Alice needs to prove that she is the actual controller of Cell#0和BTC UTXO# and demonstrate that there is indeed a binding relationship between the two.

The Implementation Principle and Supported Scenarios of Leap

The Leap function essentially allows for switching the UTXO bound to RGB++ assets, such as switching from BTC to Cardano, after which the assets can be controlled using a Cardano account. The main steps include:

1. Publish Commitment on the Bitcoin chain to declare the disconnection of the BTC UTXO from the Cell.

2. Publish Commitment on the Cardano chain, declaring the binding of the Cell to the Cardano UTXO.

3. Change the lock script of the Cell, changing the unlocking condition from Bitcoin UTXO to Cardano eUTXO.

Throughout the process, the RGB++ asset data is still stored on the CKB chain, only the unlocking conditions have changed. CKB acts as a trusted third-party witness and indexing facility during this process.

Based on the Leap function, interesting scenarios such as "full-chain transactions" can also be realized. For example, building a cross-chain trading platform where buyers can pay with BTC and receive RGB++ assets in their Cardano accounts.

Wrapper

To address the limitations of the Leap feature for native asset cross-chain, the RGB++ Layer introduces the concept of a Wrapper. Taking the rBTC wrapper as an example, it bridges BTC to the RGB++ Layer, ensuring security through fraud proofs and an over-collateralization mechanism.

By combining Leap and Wrapper, various assets in the BTCFi ecosystem, such as RGB++ native assets, BRC20, ARC20, and Runes, can realize cross-chain operations.

CKB-VM: The smart contract engine of BTCFi

CKB provides CKB-VM for RGB++ Layer, supporting various programming languages of the RISC-V virtual machine for contract development. This offers developers flexibility and lowers the entry barrier for smart contract development.

Native AA Ecosystem: Seamless Integration of BTC and RGB++

RGB++ Layer reuses CKB's native AA scheme, allowing compatibility with UTXO public chains such as BTC and Cardano on both the developer and user sides. Users can authenticate using different signature algorithms, such as BTC, Cardano, or even WebAuthn, to directly operate assets on the RGB++ Layer through accounts, wallets, or authentication methods.

This native AA solution provides the foundation for isomorphic binding and Leap functionality, which is beneficial for supporting key scenarios and optimizing the user experience.

Summary

The RGB++ Layer serves as an important infrastructure for Memecoins such as inscriptions, runes, and dye coins, enabling full-chain interaction. Its smart contract execution environment built on RiscV creates a foundation for the complex business logic of BTCFi. In the future, we will continue to monitor the progress of the RGB++ Layer and conduct more in-depth analysis of the related technical solutions.