In the blockchain industry, the term "Isomorphic Binding" first appeared in the "RGB++ Protocol Light Paper" written by Cipher, co-founder of Nervos CKB. Isomorphic Binding is one of the core technologies used by the RGB++ protocol, a layer 1 asset issuance protocol for Bitcoin. Through this technology, RGB++ can solve various problems encountered by the RGB protocol and give RGB more possibilities.
However, what many people don't know is that the Isomorphic Binding technology is not limited to empowering the RGB protocol. In fact, it can also be used in other layer 1 asset issuance protocols that use UTXO features (such as Runes, Atomical, Taproot Assets, etc.), bringing these assets Turing-complete contract extensions and performance extensions without the need for cross-chain operations or compromising security.
In today's article, we will explain in simple language the technology of Isomorphic Binding and its development prospects.
What is Isomorphic Binding?#
The prerequisite for using Isomorphic Binding technology is isomorphism. Ethereum and other EVM-based blockchains use an account model, which is a different accounting method. The difference between the UTXO model and the account model is similar to the difference between using paper money and using bank transfers in real life. Therefore, if an EVM-based blockchain wants to empower a layer 1 asset issuance protocol that uses UTXO features, it is difficult to use Isomorphic Binding technology. Instead, a traditional cross-chain bridge solution must be chosen to achieve asset transfer and performance extension through locking/minting, burning/minting, or locking/unlocking.
The Cell model of the CKB blockchain is an improved version based on the Bitcoin UTXO model, and it is closely related to the UTXO model. Therefore, we can use the Isomorphic Binding technology to bind or map the UTXOs on one blockchain to the Cells on another blockchain. Taking the RGB++ protocol as an example, since RGB assets are essentially parasitic on Bitcoin UTXOs, the RGB++ protocol can use Isomorphic Binding technology to map Bitcoin UTXOs to Cells on the CKB blockchain. This allows us to use the CKB blockchain to replace the client verification of RGB.
To better understand Isomorphic Binding technology, let's use the analogy of "land" and "deed":
- If we consider the Bitcoin mainnet as land, and Zhang San issues an asset through the RGB++ protocol, this asset is a "paper deed" corresponding to 100 acres of land. The paper deed is stored on the Bitcoin blockchain (i.e., in a UTXO that Zhang San owns). Isomorphic Binding technology is equivalent to issuing an "electronic deed" for this paper deed on the CKB blockchain (stored in a Cell that Zhang San owns).
- Zhang San transfers 40 acres of land to his relative Li Si, so the original 100-acre paper deed is destroyed and new paper deeds are generated, one for 40 acres and the other for 60 acres. They are still stored on the Bitcoin blockchain, but now the 40-acre deed is stored in a UTXO controlled by Li Si, and the 60-acre deed is stored in a UTXO controlled by Zhang San. It is important to note that the role of the Bitcoin blockchain here is to prevent Zhang San from using the 100-acre paper deed multiple times (i.e., double spending), not to verify whether the newly generated deeds add up to exactly 100 acres. In other words, under the original RGB protocol, it is up to Li Si to verify whether the deed he received says 40 acres, and Li Si also needs to verify the land source proof provided by Zhang San (the original RGB protocol requires client verification, and this verification needs to be done by the user themselves).
- The Bitcoin light client deployed on the CKB blockchain verifies the transaction of "destroying the 100-acre paper deed and generating a 40-acre paper deed and a 60-acre paper deed". After the verification is passed, the 100-acre electronic deed on the CKB blockchain is destroyed, and a 40-acre electronic deed is generated and stored in a Cell controlled by Li Si, and a 60-acre electronic deed is generated and stored in a Cell controlled by Zhang San. It is important to note that since the CKB blockchain is Turing-complete, it can verify and ensure that the newly generated electronic deeds add up to exactly 100 acres, and Li Si can see at a glance that his deed says 40 acres (because the data on the CKB blockchain is publicly visible). Therefore, the RGB++ protocol can replace the client verification of the RGB protocol, omitting the verification step for Li Si in step 2 (including land source verification).
The above 4 steps correspond exactly to the 4 processes of Isomorphic Binding technology: mapping UTXOs to Cells, verifying transactions, cross-chain verification, and state changes on CKB.
If you want to understand these 4 processes in more detail, I recommend reading the article "Isomorphic Binding: The Heartbeat of Cross-Chain Synchronization in RGB++" written by the founder of UniPass Wallet.
Security Analysis#
To better understand the security of Isomorphic Binding, let's continue using the RGB++ protocol as an example.
As mentioned earlier, the analogy of "land" and "deed" in the previous section allows us to see clearly that the security of the paper deed stored in the Bitcoin UTXO and the prevention of double spending mainly rely on the security of the Bitcoin blockchain, which is the longest-running and most secure PoW chain to date.
The security of the electronic deed generated through Isomorphic Binding technology mainly relies on the security of the CKB blockchain. From the beginning, CKB has adopted the same PoW consensus mechanism as Bitcoin, which has been tested over time and provides maximum security and decentralization. Currently, the mining machines mining CKB are produced by Bitmain, the world's largest ASIC mining machine manufacturer. The current network hashrate of CKB is approximately 271 PH/s, reaching a historical high. It is extremely difficult to forge or reconstruct a PoW chain because it requires recalculating the computational power of each block. Therefore, we can trust the security of the CKB blockchain.
Of course, you can choose not to trust and personally verify whether the deed says 40 acres and whether the land source proof provided by Zhang San is valid. This is also the practice of the RGB protocol, where users need to complete client verification themselves. The RGB++ protocol simply provides an additional option. In addition to choosing to complete client verification themselves, users can also choose to trust the verification of the CKB blockchain. In this case, the CKB blockchain is only used as a DA layer and for state disclosure. The security of the paper deed transaction is not related to CKB.
The RGB++ protocol not only allows the CKB blockchain to act as a DA layer but also supports Jump operations, allowing assets on the Bitcoin blockchain to be transferred to the CKB blockchain at any time (and vice versa). Because the CKB blockchain is Turing-complete, it can be used to build DeFi applications such as lending and DEX, allowing assets that have jumped to participate in various financial activities such as collateralized lending, staking, and trading.
The security of participating in various activities on the CKB chain with assets that have jumped depends on the security of the CKB blockchain, and as mentioned earlier, the CKB blockchain is very secure. If you still do not trust the security of the CKB blockchain, you can directly jump back to the Bitcoin blockchain after obtaining assets on the CKB chain, and they will become assets on the Bitcoin blockchain.
The risk point of the Jump function is block reorganization, which can be mitigated by waiting for confirmation from multiple blocks. On the Bitcoin chain, a transaction is considered irreversible after 6 block confirmations. The number of PoW confirmations and security is not a linear relationship, and the difficulty of overturning PoW blocks increases exponentially with the advancement of blocks. Therefore, to achieve the same level of security as 6 block confirmations on the Bitcoin blockchain, approximately 24 block confirmations are needed on the CKB blockchain. The average block time of CKB is about 10 seconds, so the time for 24 block confirmations is actually much lower than the time for 6 block confirmations on Bitcoin.
Diagram illustrating the security of PoW (not theoretical calculation)
Therefore, if you want better security, you can choose to wait for more block confirmations. If you want to balance user experience, you need to make some trade-offs and optimize the product. For more discussions on the security of RGB++, I recommend reading "RGB++ Deep Dive (1): Security Analysis".
Development Prospects of Isomorphic Binding Technology#
As mentioned earlier, Isomorphic Binding technology is not limited to empowering the RGB protocol. In fact, it can also be used in other layer 1 asset issuance protocols that use UTXO features. The following diagram illustrates the versatility of Isomorphic Binding technology:
From the diagram, we can see that by using Isomorphic Binding technology, we can bind or map assets issued by layer 1 asset issuance protocols such as Runes, Atomical, Taproot Assets, etc., on the Bitcoin blockchain to Cells on the CKB blockchain. This brings these assets Turing-complete contract extensions and performance extensions without the need for cross-chain operations or compromising security.
In addition to assets issued on the Bitcoin layer, we can also use Isomorphic Binding technology to map assets issued on other UTXO-based blockchains (such as Dogechain, Ergo, BCH, BSV, LTC, etc.) to Cells on the CKB blockchain. This is a very imaginative blueprint. With the addition of Jump operations, the CKB blockchain becomes a marketplace for all UTXO-based encrypted assets, where "all roads lead to CKB".
Conclusion#
Isomorphic Binding technology originated from the RGB++ protocol. RGB++ uses Isomorphic Binding to map Bitcoin UTXOs to Cells on the Nervos CKB blockchain, solving technical problems encountered by the original RGB protocol and providing more possibilities. However, Isomorphic Binding technology is not limited to empowering the RGB protocol or the Bitcoin layer. In fact, it can be used in any layer 1 asset issuance protocol that uses UTXO features. By utilizing Jump technology, it brings Turing-complete contract extensions and performance extensions to these assets without the need for cross-chain operations or compromising security.
UTXO is a prerequisite for Isomorphic Binding technology, and PoW provides sufficient security for Isomorphic Binding. CKB, as a UTXO+PoW chain, will showcase the brilliance of Isomorphic Binding technology. In the near future, we may see a scene where "all roads lead to CKB".