This article explores CKB's UTXO-based public blockchain and its technical approach to Bitcoin Layer 2 solutions, shedding light on this emerging category of Bitcoin scaling.
Since the launch of Ordinals & inscriptions on Bitcoin, the network has experienced renewed interest and activity. While protocols like Ordinals enhance Bitcoin's programmability, they primarily leverage Bitcoin's limited scripting capabilities (e.g., "op_if" opcode) rather than enabling true smart contract functionality. As Bitcoin fundamentally operates as a decentralized ledger with non-Turing-complete scripting, these assets remain largely confined to trading. Thus, developing robust Layer 2 (L2) solutions for smart contract execution becomes imperative for Bitcoin's ecosystem growth.
Current Bitcoin L2 solutions can be broadly categorized into:
- State channels (e.g., Lightning Network)
- Sidechains (e.g., Liquid, Merlin)
- Rollups (e.g., Rollkit)
- Client-side validation (e.g., RGB, RGB++, Taro)
Given market trends, Bitcoin L2 projects today predominantly fall into two camps:
- EVM Camp: Projects like Merlin and B² that prioritize EVM compatibility and staking incentives.
- UTXO Camp: Native UTXO-model proponents like CKB, which recently proposed the RGB++ extension protocol.
Technical Primer: UTXO Model & RGB Protocol
UTXO vs. Account Models
- Account Model: Used by Ethereum, resembles bank accounts with visible balances (easier for users).
- UTXO Model: Bitcoin's approach, where transactions consume "unspent transaction outputs" like physical cash (critical for understanding RGB).
RGB Protocol
RGB improves upon Ordinals by:
- Binding assets to UTXOs (not individual satoshis)
- Storing only transaction commitments on-chain (hash values), moving validation off-chain
- Enabling client-side verification to reduce Bitcoin network congestion
Key RGB innovations:
- Single-use Seals: Asset ownership tied to UTXOs
- Client Validation: Off-chain transaction verification between parties
RGB Challenges
- Data availability (DA) issues
- Underdeveloped P2P network
- Immature virtual machine (AluVM)
- Limited multi-party contract support
CKB's RGB++: A Next-Gen Bitcoin L2 Solution
CKB's Evolution
Originally launched in 2019 as a PoW chain with generalized UTXO (Cell model), CKB is now positioning itself as Bitcoin's first fully isomorphic L2 (PoW+UTXO).
RGB++ Protocol
Introduced in February 2024, RGB++ enhances RGB by:
- Isomorphic Binding: Maps Bitcoin UTXOs to CKB Cells
- On-Chain Verification: Uses CKB to publicly validate RGB++ transactions
- Non-Interactive Transfers: Eliminates recipient online requirements
Advantages over RGB:
- Resolves DA issues via CKB's blockchain-as-client
- Enables transaction folding (multiple CKB tx ↔ single Bitcoin tx)
- Maintains Bitcoin's security without bridges
CKB's Competitive Edge & Roadmap
UTXO vs. EVM Camp Comparison
- EVM Camp: Faster adoption via staking incentives
- UTXO Camp: Technical superiority through native Bitcoin compatibility
Upcoming Milestones
- RGB++ mainnet launch (April 2024)
- Bitcoin conferences (Singapore March 2024, Hong Kong April 2024)
- Lightning Network integration (Long-term goal)
👉 Explore Bitcoin L2 innovations
FAQs
Q: How does RGB++ differ from Ordinals?
A: While Ordinals bind data to satoshis, RGB++ uses UTXO-based asset binding and off-chain validation for better scalability.
Q: Is CKB a sidechain?
A: No, it's a UTXO-model L2 that maintains Bitcoin's security model without bridges.
Q: Why choose UTXO over EVM for Bitcoin L2?
A: UTXO models provide native compatibility with Bitcoin, preserving its security properties.
Q: When can developers start building on RGB++?
A: The protocol will be available for mainnet deployment in Q2 2024.
👉 Discover more about UTXO innovation
Conclusion
Once considered niche for sticking to PoW+UTXO architecture, CKB has emerged as a technical leader in Bitcoin L2 solutions. With RGB++ offering Turing-complete smart contracts while maintaining Bitcoin's security, CKB demonstrates that thoughtful protocol design can advance Bitcoin's capabilities without compromising its core principles. As the Bitcoin L2 narrative matures, projects combining technical rigor with ecosystem adoption—like CKB—are poised to play pivotal roles in Bitcoin's evolving landscape.