Chinese Version: 一文看懂同构绑定技术及其发展前景

The concept of 'isomorphic binding' initially emerged within the blockchain domain, as introduced in the RGB++ Protocol Light Paper authored by Cipher from Nervos CKB. This technology plays a pivotal role in RGB++, a groundbreaking asset issuance protocol on Bitcoin's layer 1. It addresses and resolves various challenges encountered by its forerunner, RGB, thereby augmenting RGB with expanded functionalities and capabilities.

What many people don't realize, however, is that isomorphic binding technology is not limited to empowering RGB protocols; in fact, it can also be used in other layer 1 asset issuance protocols that utilize UTXO features (e.g., Runes, Atomical, Taproot Assets, etc.) to bring Turing-complete contract extensions and improving performance to these assets without the need to cross-chain and without loss of security.

In this article, we will introduce you to the technology of isomorphic binding and its prospects in plain language.

Isomorphic Binding in a Nutshell

The foundation of isomorphic binding technology rests on the principle of isomorphism. EVM-based blockchains, like Ethereum, adopt the account model, a distinct accounting approach from the UTXO model used by Bitcoin. The differences between these models are akin to the differences between handling transactions in cash versus bank transfers in everyday life. Consequently, integrating isomorphic binding technology into EVM blockchains to enhance layer 1 asset issuance protocols leveraging UTXO traits poses a significant challenge. Instead, these blockchains typically resort to conventional cross-chain bridge solutions to facilitate asset transfers and scalability, employing mechanisms such as lock/mint, burn/mint, or lock/unlock to manage assets.

The Cell model, implemented by the CKB blockchain, represents an improved version of the traditional UTXO model, sharing a common lineage. This similarity enables the application of isomorphic binding technology to map UTXOs from one blockchain to another. For instance, within the context of the RGB++ protocol, since RGB assets are intrinsically tied to Bitcoin's UTXO, isomorphic binding can be used to map these Bitcoin UTXOs to Cells on the CKB blockchain. This facilitates the replacement of client-side verification (CSV) in RGB with blockchain-based verification on CKB.

To elucidate the concept of isomorphic binding, consider the analogy of land and deeds:

1. Imagine the Bitcoin network as a tract of land. Through the RGB++ protocol, Alice issues an asset, akin to a deed for a 100-acre parcel, recorded on the Bitcoin blockchain as a UTXO, which Alice owns. Isomorphic binding acts like creating an electronic version of this land deed on the CKB blockchain, stored in a Cell owned by Alice.
2. When Alice transfers 40 acres to Bob, the original 100-acre deed is destroyed (spent), and new deeds for 40 and 60 acres are created and recorded on the Bitcoin blockchain, with Bob and Alice owning their respective UTXOs. It's crucial to note that the Bitcoin blockchain's role is primarily to prevent double-spending, not to verify the exact division of acreage. Under the original RGB protocol, Bob would need to personally verify the specifics of his 40-acre deed and its provenance—a process required to be conducted by the receiver.
3. A Bitcoin light client on the CKB blockchain then verifies the transaction that split the original 100-acre deed into new 40 and 60-acre deeds, ensuring its legitimacy.
4. Upon successful verification, the 100-acre electronic deed on the CKB blockchain is destroyed (spent) and replaced with new 40 and 60-acre electronic deeds, stored in two different Cells under Bob and Alice's control, respectively. Given CKB's Turing-complete capabilities, it can confirm that the sum of the new deeds equals the original 100 acres, offering transparent verification to Bob without the need for manual checks. Thus, the RGB++ protocol effectively supersedes the original RGB protocol's client-side verification (CSV) requirement, streamlining the process.

These steps outline the isomorphic binding process: mapping of UTXOs to Cells, transaction verification, cross-chain verification, and state update on CKB.

For a deeper dive into these processes, consider reading "Isomorphic Binding: The Heartbeat of Cross-Chain Synchronization in RGB++" by Frank, the founder of UniPass Wallet.

Security Analysis

To elucidate the security mechanisms of isomorphic binding, we'll examine the RGB++ protocol as a case study.

The analogy between land and deeds above makes it clear that the security and prevention of double spending of deeds stored in Bitcoin UTXO relies heavily on the security of the Bitcoin blockchain, which is most established and secure proof-of-work (PoW) chain to date.

The security and prevention of double spending of the electronic land deeds created via isomorphic binding technology hinges on the CKB blockchain's security. CKB has adopted the same time-tested PoW consensus mechanism as that of Bitcoin from the beginning to maximize security and decentralization. Currently, CKB's mining machines are produced by the world's largest AISC miner, Bitmain, and CKB's current network hash rate is about 279 PH/s, a record high. It is extremely difficult to forge or reorganize a PoW chain, as the hash rate of each block needs to be recalculated, so we can trust the security of the CKB blockchain.

Nonetheless, you can also choose not to trust it. Then all you need to do is the second step in the above example—confirming the details of the land deed (e.g., verifying a 40-acre parcel) and the authenticity of the traceability certificate provided by Alice. This process mirrors the original RGB protocol's reliance on client-side verification, which users must undertake independently. The RGB++ protocol simply offers an alternative: trusting CKB's blockchain verification in lieu of manual validation. Here, the CKB blockchain serves as a Data Availability (DA) layer and a medium for state disclosure, and the security of land deed transactions on Bitcoin has nothing to do with CKB.