In the previous article “The Cornerstone of RGB and RGB++ Protocols: One-Time Sealing and Client Verification”, we briefly introduced the differences in verification methods between the RGB and RGB++ protocols: RGB requires users to run the client for verification, while RGB++ simplifies user operations by utilizing isomorphic binding to achieve asset verification through a Turing-complete UTXO blockchain (such as Nervos CKB) (of course, users can still choose to verify themselves).
For asset issuance protocols, security is always the primary consideration. In today’s article, we will continue to introduce RGB++, detailing what isomorphic binding is and why the RGB++ protocol is considered extremely secure.
What is Isomorphic Binding?#
The use of isomorphic binding technology is predicated on isomorphism. The Cell model of the CKB blockchain is an advanced version of the Bitcoin UTXO model, both originating from the same root. This similarity allows us to use isomorphic binding technology to bind or map UTXOs from one blockchain to UTXOs on another blockchain. Taking the RGB++ protocol as an example, since RGB assets essentially parasitize Bitcoin UTXOs, the RGB++ protocol can utilize isomorphic binding technology to map Bitcoin UTXOs to Cells on the CKB blockchain, allowing us to use the CKB blockchain to replace the client verification of the RGB protocol.
To intuitively understand isomorphic binding technology, we can use land and land deeds as analogies:
- If we compare the Bitcoin mainnet to land, and Zhang San issues an asset through the RGB++ protocol, this asset is a paper land deed corresponding to 100 acres of land. The paper land deed is stored on the Bitcoin blockchain (i.e., in UTXOs, with Zhang San owning this UTXO), and the isomorphic binding technology is equivalent to issuing a corresponding electronic version of the land deed on the CKB blockchain (stored in Cells).
- Zhang San transfers 40 acres of land to his relative Li Si, thus the original 100-acre paper land deed is destroyed, generating a new paper land deed, one for 40 acres and another for 60 acres, still stored on the Bitcoin blockchain. The difference is that the 40-acre deed is stored in a UTXO controlled by Li Si, while the 60-acre deed is stored in a UTXO controlled by Zhang San. It should be noted that the role of the Bitcoin blockchain here is to prevent Zhang San from using the 100-acre paper land deed multiple times (i.e., double spending), rather than verifying whether the new land deeds’ total area equals exactly 100 acres. In other words, under the original RGB protocol, whether the deed Li Si receives states 40 acres needs to be verified by Li Si himself, and he also needs to verify the land provenance proof provided by Zhang San (the original RGB protocol requires client verification, which users must perform themselves).
- The Bitcoin light client deployed on the CKB blockchain verifies the event of “destroying the 100-acre paper land deed and generating a 40-acre paper land deed and a 60-acre paper land deed” that occurs on the Bitcoin blockchain, confirming whether it actually happened.
- After verification, the 100-acre electronic land deed on the CKB blockchain is destroyed, generating a 40-acre electronic land deed and a 60-acre electronic land deed. It is important to note that since the CKB blockchain is Turing-complete, it can verify and ensure that the total area of the newly generated two electronic land deeds equals exactly 100 acres, and Li Si can see at a glance that his deed states 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 Li Si's verification in step 2 (including land provenance verification).
The above four steps correspond exactly to the four operational processes of isomorphic binding technology: mapping UTXOs to Cells, verifying transactions, cross-chain verification, and state changes on CKB.
Security Analysis#
From the analogy of land and land deeds, we can clearly see that the security and prevention of double spending of the paper land deed stored in Bitcoin UTXOs mainly rely on the security of the Bitcoin blockchain. And Bitcoin, as the longest-running and most secure PoW chain, has proven its security over time.
The security and prevention of double spending of the electronic land deed generated through isomorphic binding technology mainly depend on the security of the CKB blockchain. CKB has adopted the same, time-tested PoW consensus mechanism as Bitcoin from the very beginning, maximizing security and decentralization. Currently, CKB's mining equipment is produced by Bitmain, the world's largest ASIC miner manufacturer, and CKB's current total network hashrate has surpassed 440 PH/s, setting a historical high. It is extremely difficult to forge or reconstruct a PoW chain, as this requires recalculating the hashrate of each block, akin to attempting to rebuild a pyramid overnight, which is nearly impossible. Therefore, we can fully trust the security of the CKB blockchain.
Of course, if you still have doubts, you can choose to verify personally, just like in the second step of the example above, to confirm whether the deed indeed states 40 acres and whether the land provenance proof provided by Zhang San is genuine and valid. This is also the approach of the RGB protocol, where users need to complete client verification themselves; the RGB++ protocol merely provides an additional option, allowing users to choose to trust the verification of the CKB blockchain instead of completing client verification themselves. Here, the CKB blockchain serves only as a DA layer and status publicization, and the security of the paper land deed transaction is even indirectly related to CKB.
The charm of the RGB++ protocol lies not only in having the CKB blockchain serve as a DA layer, but it also supports Leap operations, allowing RGB++ assets on the Bitcoin blockchain to freely traverse the CKB blockchain (of course, reverse operations are also possible, and it can be expanded to other Turing-complete UTXO blockchains in the future). Since the CKB blockchain is Turing-complete, developers can build various complex DeFi applications on it, such as lending platforms, decentralized exchanges, etc. This means that RGB++ assets transferred to the CKB blockchain through Leap operations can participate in a rich variety of financial activities, such as collateralized lending, staking for interest, trading, and more.
When you hold RGB++ assets transferred to the CKB chain through Leap operations and participate in various financial activities, the security of these operations mainly relies on the security of the CKB blockchain. As we discussed earlier, the CKB blockchain itself has high security. However, if you still have concerns about the security of the CKB blockchain, you can always choose to transfer the RGB++ assets on the CKB chain back to the Bitcoin blockchain through Leap operations, turning them back into RGB++ assets on the Bitcoin blockchain.
Speaking of the Leap function, we must mention the risks it may face — block reorganization. However, this risk can be effectively mitigated by waiting for more block confirmations. In the Bitcoin network, transactions are generally considered irreversible after 6 block confirmations. It is worth noting that the number of confirmations in PoW is not linearly related to security; the difficulty of overturning PoW blocks increases exponentially with the number of blocks. Therefore, on the CKB blockchain, to achieve security equivalent to 6 block confirmations in Bitcoin, approximately 24 CKB block confirmations are needed. Considering that the average block time of CKB is about 10 seconds, the time required for 24 block confirmations is actually much shorter than that required for 6 block confirmations in Bitcoin.
Figure: A diagram of PoW security; Source: https://talk.nervos.org/t/rgb-1/7798
So, if you want to obtain higher security assurance, you only need to wait for a few more block confirmations.
Conclusion#
The isomorphic binding technology used by RGB++ cleverly binds Bitcoin's UTXO with CKB's Cells, not only simplifying user verification operations but also maintaining high security. At the same time, Leap operations provide users with broader application scenarios, opening new avenues for cross-chain interoperability.
As more and more applications choose to build on the RGB++ foundation, we have reason to believe that it will play an increasingly important role in the future Bitcoin ecosystem.