Current situation
Traditional cross-chain solutions heavily rely on bridges using a lock-mint or burn-mint pattern. Aside from the risk of collusion among cross-chain bridges’ multi-signature parties, these bridges have always been attractive targets for hackers, because they often feature a central storage point of funds that back the bridged assets on the receiving blockchain. It is estimated that over $2 billion in cryptocurrency was stolen across multiple cross-chain bridge attacks in 2022 alone.
Introducing RGB++ and Leap
The RGB++ protocol has pioneered a new paradigm, named “Leap”, enabling the cross-chain transfer of RGB++ assets without the need for bridges. It sounds like a fantasy, but how is it achieved?
The RGB++ protocol maps Bitcoin UTXOs to the eUTXOs (extended UTXOs with smart contract capabilities) of a Turing-complete UTXO chain through isomorphic binding. This Turing-complete UTXO chain, called the RGB++ layer, is employed to efficiently manage state changes and transaction verification. It could be Nervos CKB, Cardano or any other UTXO-based Turing-complete chain.
Isomorphic binding refers to the mutual binding of Bitcoin UTXOs and eUTXOs on the RGB++ layer, where the unlocking condition of the eUTXO is set to the corresponding UTXO being spent. Therefore, once the UTXO is spent, the corresponding eUTXO is transferred as well.
Example of RGB++ asset transfer
For example, when Alice issues 100 TEST tokens through the RGB++ protocol, it is represented on the Bitcoin blockchain as a dust UTXO received by Alice’s Bitcoin address.
Simultaneously, an eUTXO is generated on the RGB++ Layer, containing the definition for the RGB++ assets (i.e., the 100 TEST tokens) and its unlocking condition — this eUTXO will be spent only if Alice’s dust UTXO is spent. In this way, Alice’s dust UTXO is associated with the 100 TEST tokens.
When Alice transfers 60 TEST tokens to Bob, it is represented on the Bitcoin blockchain by Alice spending the original UTXO associated with the 100 TEST tokens. Alice receives a new dust UTXO associated with 40 TEST tokens, while Bob’s address receives a dust UTXO associated with 60 TEST tokens.
On the RGB++ Layer, the original eUTXO is spent and two new eUTXOs are generated: one containing the definition for 40 TEST tokens and the other for 60 TEST tokens. Both new eUTXOs have the unlocking condition that they will be spent only if their corresponding Bitcoin UTXOs (held respectively by Alice and Bob) are spent.
UTXO is the key to Leap
From the example above, we can see that issuing RGB++ assets on the Bitcoin blockchain through the RGB++ protocol essentially involves associating them with Bitcoin UTXOs. These RGB++ assets have their definition on the RGB++ layer, while their ownership is tied to Bitcoin UTXOs through the unlocking conditions of eUTXOs. These assets are considered Bitcoin Layer 1 assets because their ownership is tied to Bitcoin Layer 1.
Imagine such a situation: what if the unlocking condition of an eUTXO is set to another chain’s UTXO being spent, say, Litecoin’s UTXO? This would mean the ownership of the asset is tied to the Litecoin chain instead, and it should be considered a Litecoin chain asset. The asset magically leaps from the Bitcoin chain to the Litecoin chain — it is “bridged” across chains without a bridge!
Therefore, in the example mentioned above, if Alice wants to transfer her 40 TEST tokens (a Bitcoin Layer 1 asset) to the Litecoin chain, she first needs to spend the corresponding Bitcoin UTXO. Then, a transaction should be constructed on the RGB++ Layer to change the unlocking condition of the eUTXO (containing the asset definition) to her Litecoin UTXO. In this way, the leap from the Bitcoin chain to the Litecoin chain is successful because the ownership (UTXO as unlocking condition) is transferred across chains.
The Bitcoin chain and Litecoin chain in this example can be replaced with any two UTXO-based chains. Such cross-chain leaps are elegant and straightforward, something that only the UTXO model can achieve.
Advantages of Leap
Safe
In traditional cross-chain solutions, users must stake or lock their crypto assets into a multi-signature address, trusting that the operators of the cross-chain bridge will not act maliciously. Once the assets are locked, they are no longer under the user’s control.
The bridgeless cross-chain Leap is superiorly more secure because the assets move directly from one point to another, and their ownership is always controlled by the user’s private key. The entire process of Leap is fully decentralized and requires no trust assumptions.
Permissionless
Due to cost considerations, operators of traditional cross-chain bridges often only support a limited number of top assets for cross-chain transfers, neglecting niche assets.
However, Leap does not have this issue. It is permissionless. Anyone can issue a meme coin on the Bitcoin blockchain using the RGB++ protocol and have it leap to other UTXO blockchains freely at any time.
Comparison between traditional cross-chain bridge and Leap
Conclusion
Bridgeless cross-chain Leap is an unparalleled feature introduced by the RGB++ protocol and a significant advantage of the UTXO model. It will change the current situation where cross-chain solutions heavily rely on risky bridges.
UTXO Stack is building infrastructure to help developers create Bitcoin Layer 2 chains based on the UTXO model, where bridgeless cross-chain Leap will become a highlight. Leap allows RGB++ assets to move freely between UTXO chains, opening up new possibilities for Bitcoin Layer 2 scaling.
