RGB++ homomorphic binding and its security

Source: Nervos CKB

For asset issuanceprotocol, security is always the primary consideration. In today’s article, we will continue to introduce RGB++, detail what is homomorphic binding, and why the RGB++ protocol is considered extremely secure.

What is Isomorphic Binding?

The premise of using isomorphic binding technology is isomorphism. The Cell model of the CKB Block chain is an advanced version of the BTC UTXO model, and they have the same roots. This similarity allows us to use isomorphic binding technology to bind or map the UTXO of a Block on-chain to the UTXO of another Block chain. Taking the RGB++ protocol as an example, since the RGB assets are essentially parasitic on the BTC UTXO, the RGB++ protocol can use isomorphic binding technology to map BTC UTXO to the Cell of the CKB Block chain, so that we can use the CKB Block chain to replace the client verification of the RGB protocol.

To better understand the technology of homomorphic binding, we use land and title deeds as analogous objects:

1. If we regard BTCMainnet as land, Zhang San issued an asset through the RGB++ protocol, which is a paper deed corresponding to 100 acres of land. The paper deed is stored on BTCBlockon-chain (i.e., UTXO, owned by Zhang San), and homomorphic binding technology is equivalent to issuing a corresponding electronic version of the deed on the CKB Blockon-chain (stored in Cell).
2. Zhang San transferred 40 mu of land to his relative Li Si, so the original 100 mu paper land deed was destroyed and new paper land deeds were generated. One paper land deed is for 40 mu, and the other is for 60 mu. They are still stored on the BTCBlock on-chain. The difference is that the 40 mu land deed is stored in the UTXO controlled by Li Si, and the 60 mu land deed is stored in the UTXO controlled by Zhang San. It should be noted that the role of the BTCBlock chain here is to prevent Zhang San from using the 100 mu paper land deed multiple times (i.e., double spending), not to verify whether the total area of the newly generated land deeds is exactly 100 mu. In other words, under the original RGB protocol, Li Si needs to verify for himself whether the land deed he receives is for 40 mu, and he also needs to verify the land source proof provided by Zhang San (the original RGB protocol requires client verification, and client verification requires users to do it themselves).
3. Deploy a BTC light client on the CKB Block on-chain to verify the event of “destroying a 100-acre paper land deed and generating a 40-acre paper land deed and a 60-acre paper land deed” that occurred on the BTC Block chain, and verify if it actually happened.
4. After verification, the on-chain CKB Block’s 100 mu electronic version of the land deed is destroyed, generating a 40 mu electronic version of the land deed and a 60 mu electronic version of the land deed. It should be noted that, because the CKB Block chain is Turing Complete, it can verify and ensure that the combined area of the two newly generated electronic land deeds is exactly 100 mu. Li Si can also see at a glance that his land deed indicates 40 mu (because the on-chain data of CKB Block 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 tracing verification).

The above 4 steps correspond exactly to the 4 operation processes of homomorphic binding technology: mapping UTXO to Cell, verifying transactions, cross-chain interaction verification, and state changes on CKB.

Security Analysis

The analogy of land and title deeds in the previous section allows us to clearly see that the security and prevention of double spending of the paper title deeds stored in BTC UTXO mainly depend on the security of the BTC blockchain. And BTC, as the longest-running and most secure PoW chain, has withstood the test of time in terms of security.

The electronic version of the land certificate generated through homomorphic binding technology relies mainly on the security and prevention of double spending of the CKB Blockchain. CKB has adopted the PoW Consensus Mechanism that is identical to BTC and has been tested over time from the beginning, ensuring maximum security and Decentralization. Currently, CKB’s Mining equipment is produced by the world’s largest ASIC Mining Rig manufacturer Bit Mainland, and the current overall Computing Power of CKB has exceeded 440 PH/s, reaching a historic high. It is extremely difficult to forge or reconstruct a PoW chain, as this would require recalculating the Computing Power for each Block, which is almost impossible to accomplish, like trying to rebuild a pyramid overnight. Therefore, we can fully trust the security of the CKB Blockchain.

Of course, if you still have doubts, you can also choose to verify it yourself, just like the second step in the example above, to confirm whether the deed really states 40 mu and whether the land tracing proof provided by Zhang San is genuine and valid. This is also the practice of the RGB protocol, where users need to complete client verification themselves; RGB++ protocol simply provides an alternative choice, in addition to choosing to complete client verification themselves, they can also choose to trust the verification of the CKB blockchain. The CKB blockchain is only used here as the DA layer and state disclosure, and the security of paper deed transactions has no direct relationship with CKB.

The charm of the RGB++ protocol lies not only in enabling the CKB Block chain to act as the DA layer, but also in supporting Leap operations, allowing BTC Block on-chain RGB++ assets to freely shuttle on the CKB Block on-chain (of course, Reverse operations are also possible, and can also be extended to other Turing Complete UTXO blockchains in the future). Because the CKB Block chain is Turing Complete, developers can build various complex Decentralized Finance applications on it, such as lending platforms, Decentralization exchange, etc. This means that RGB++ assets transferred to the CKB Block on-chain through Leap operations can participate in a variety of financial activities, such as collateralized lending, stake earning, trading, etc.

When you hold RGB++ assets transferred through Leap operation to CKB on-chain and participate in various financial activities, the security of these operations mainly depends on the security of the CKB Block chain. As we discussed earlier, the CKB Block chain itself has very high security. However, if you still have doubts about the security of the CKB Block chain, you can choose to transfer the RGB++ assets on CKB on-chain back to the BTC Block chain through Leap operation at any time, making it reappear as RGB++ assets on BTC Block on-chain.

When it comes to the Leap function, we have to mention the risk it may face - Block reorganization. However, this risk can be effectively avoided by waiting for more Block confirmations. In the BTC network, transactions are generally considered irreversible after 6 Block confirmations. It is worth noting that the number of confirmations for PoW is not linearly related to security, and the difficulty of overturning PoW Blocks rises exponentially with the increase of Blocks. Therefore, in the CKB Block on-chain, to achieve the same level of security as 6 Block confirmations in BTC, it is estimated that only about 24 CKB Block confirmations are needed. Considering that the average block time of CKB is about 10 seconds, the time for 24 Block confirmations is actually much less than the time required for 6 Block confirmations in BTC.

Image: Illustration of PoW security; Source:

So, if you want to get higher security assurance, just wait for a few more Block confirmations.

Conclusion

The homomorphic binding technology used by RGB++ cleverly binds the UTXO of BTC with the Cell of CKB, which not only simplifies the user’s verification operation, but also maintains a high level of security. At the same time, the Leap operation provides users with a wider range of application scenarios, opening up new avenues for Cross-Chain Interaction interoperability.

With more and more applications choosing to build on top of RGB++, we have reason to believe that it will play an increasingly important role in the future BTC ecosystem.