Seamless Moves: RGB++ Ports Assets Across Blockchains Without Cross-Chain Bridges

14 Jun 2024

Cross-chain bridges exist to solve a major pain point in the blockchain sphere: the lack of interoperability. That is, due to incompatibility, assets on different blockchains are unable to port into one another.

Bridges typically rely on multi-signature (multisig) setups that require high trust levels to perform their function. As a result, they have opened up new markets and have been crucial to many blockchain platforms for the transfer of crypto assets from one platform to another.

However, as useful as cross-chain bridges seem to have become, so have they struggled with their vulnerability to attacks from evil hackers. When exploited, a problem of users’ funds being at risk of fraud and malicious actions arises. Bridges have been frequent targets for hackers, as demonstrated by several high-profile breaches resulting in losses estimated at $2 billion:

  • In July 2021, the ChainSwap cross-chain asset bridge was attacked, losing nearly $8 million
  • In January 2022, Qubit Finance's bridge suffered a hack, resulting in losses of over $80 million
  • In February 2022, the Wormhole bridge was hacked with losses exceeding $320 million
  • In August 2022, over $190 million in crypto assets were stolen from the Nomad bridge

These call to question more decentralized alternatives relying less on trust, while they suffer from poor user experience and technical complexity.

What RGB++, a groundbreaking Bitcoin Layer 1 asset standard does, is offering a unique solution to this significant threat to building trust in blockchain technology. It enables crypto assets on its protocol to move across blockchains without cross-chain bridges and their associated drawbacks.

The RGB++ Protocol appears as the industry’s current single most effective way to issue and transfer crypto assets on the secure Bitcoin blockchain without running a client-side verification. Through its features that give the ability to "leap" assets directly between L1 (Bitcoin blockchain) and L2 (CKB blockchain or other UTXO-based blockchains), RGB++ enables cross-chain transfers without bridges, permissions, or trust assumptions as well as the attendant vulnerabilities.

This article unpacks the mechanics and benefits of this innovative, bridge-free cross-chain solution.

The Leap as a Bridge-Free Cross-Chain Mechanism

The bridge-free cross-chain solution thrives as a leap on the minting and ownership transfer capability of RGB++ assets. The RGB++ protocol issues crypto assets on the Bitcoin blockchain that are "tied" or "bound" to Bitcoin's UTXO with 546 satoshi which, if spent will see the corresponding RGB++ asset spent too.

For example, if Alice mints 100 Test tokens via RGB++ protocol, there will be a 546 satoshi-UTXO on the Bitcoin blockchain under her control and associated with the 100 Test tokens. Simultaneously, since assets issued via RGB++ create corresponding "shadow assets'' on the CKB blockchain, a cell is created on the CKB blockchain. This essentially produces a smarter UTXO containing the interpretation of the RGB++ assets (i.e. the 100 Test tokens) and their unlocking condition. Only when Alice's 546 satoshi-UTXO has been spent will the cell be concurrently spent as well.

So, when Alice transfers 60 Test tokens to Bob, it reflects on the Bitcoin blockchain that she has spent the original UTXO associated with the 100 Test tokens. She will receive a new 546 satoshi-UTXO linked to the remaining 40 Test tokens as the original cell on the CKB blockchain creates two new cells—one containing the interpretation of 40 Test tokens and another with 60 Test tokens. Meanwhile, Bob's address receives a UTXO associated with 60 Test tokens.

This example shows that the ownership of RGB++ assets is tied to Bitcoin's UTXOs. Only whoever transfers (spends) a particular UTXO can unlock the corresponding RGB++ assets. This is because the unlocking condition set in the cell containing the RGB++ asset interpretation is the transfer of the Bitcoin UTXO.

When the unlocking condition of an RGB++ transaction initiated on the Bitcoin blockchain is set with a UTXO from another blockchain (not Bitcoin), the asset "leaps" to the other blockchain. The next spending of the RGB++ asset would have to be unlocked by a UTXO from that blockchain. This is the basic mechanism of the leap, a bridge-free cross-chain solution that is entirely decentralized and requires no trust assumptions. To dive deeper, watch Cipher’s talk on the "Overview of the BTC Layer 1 Asset Protocol".

Benefits of the Leap Feature

The leap feature stands out for being permissionless, trustless, secure, and efficient:

  • Permissionless: Unlike multisig bridges that restrict the type of assets they support, the leap feature allows any asset minted on the Bitcoin blockchain to move freely to and from the CKB blockchain.

  • Trustless: It operates without any need for intermediary trust i.e. no assets are held or controlled by a third party.

  • Secure: By avoiding central points of vulnerability like those in multisig bridges, the security of RGB++ assets is greatly enhanced.

  • Efficient: Although requiring multiple block confirmations may take about an hour, this delay is generally acceptable and ensures greater safety and reliability.

The leap also supports both the fungible and non-fungible tokens (such as DOBs (or Digital Objects) issued through the Spore Protocol on the CKB blockchain), enhancing its utility across different asset types.

Tutorial on Using the Leap Feature with the JoyID Wallet

The JoyID wallet supports easy leaping of RGB++ assets (coins and DOBs) between Bitcoin and CKB blockchains. Here’s how:

1. From L1 to L2 (BTC → CKB)

Leaping RGB++ assets (coins and DOBs) from L1 (Bitcoin blockchain) and L2 (CKB blockchain) is quite easy. Follow these steps:

  1. After logging into the JoyID wallet, switch to the Bitcoin network

  2. Click the 'Leap' button and select the coin(s) or DOB(s) you want to leap

  3. In the sending interface, select “Bitcoin L2 (CKB)” then enter the CKB address and the quantity. Set the miner fee.

  4. Click “Send” and confirm with your Touch ID or Face ID.

A video tutorial can be found here.

2. From L2 to L1 (CKB → BTC)

Leaping RGB++ assets (coins and DOBs) from L2 to L1 is in two stages: the prepare and complete stages which require signing BTC and CKB transactions respectively.

Prepare the leap

  1. After logging into the JoyID wallet, switch the network to Nervos CKB
  2. Click the "Leap" button
  3. Enter your Bitcoin address
  4. Select the RGB++ asset(s) you want to leap back to L1 and specify the amount
  5. Choose a FeeRate (ensure your Bitcoin wallet has a sufficient UTXO balance for the fee)
  6. Click the "Leap to Bitcoin L1" button
  7. Click the "Prepare" button
  8. Sign to confirm the transaction
  9. Click "Track Status" to monitor the progress. You can also view it in "Ongoing Leaps"

Complete the leap

  1. Wait for the Bitcoin mainnet to confirm the transaction. Once confirmed, click "Complete".
  2. Verify the leap details and click "Complete" again. Wait for the CKB mainnet to confirm the transaction, which you can track in settings-activity-leap.
  3. After the CKB mainnet confirmation, switch to your Bitcoin wallet to view your RGB++ asset(s).

A video tutorial can be found here.

3. Notice

RGB++ assets are bound to Bitcoin's UTXOs that are sized at 546 satoshis. If this UTXO is spent, the associated RGB++ assets are also spent or burned.

To prevent UTXOs bound to RGB++ assets from being spent accidentally, JoyID wallet has set a threshold—which is currently 1200 satoshi. UTXOs below this amount will not be spent as miner's fees or normal BTC transfers. To avoid being mistakenly spent, it is recommended that you use a JoyID wallet to store and send/receive RGB++ assets.

Avoid using some of the tools made by community members to leap assets from the CKB blockchain to the Bitcoin blockchain. They don't usually adhere to the RGB++ standard when binding to Bitcoin's 546 satoshi-UTXOs. If they bind an asset to a UTXO with more than 1200 satoshi, then a transaction sent using a JoyID wallet will easily spend the UTXO as the miner's fee or for regular UTXO transactions.

It is recommended to use only the JoyID wallet for all leap operations. For further guidance, refer to the "JoyID Passkey Wiki".