At the mid of 2023, with the rise of the Ordinals protocol and the BRC-20 standard, the Bitcoin ecosystem saw significant wealth opportunities, attracting the attention of many developers and investors. As a result, user-friendly asset management tools and trading platforms became crucial, leading to the rapid popularity of Unisat, a browser-based wallet focusing on the Ordinals protocol and BRC-20 standard. Leveraging its first-mover advantage, Unisat has captured a significant market share.
While the previous wave of inscriptions brought immense wealth to the Bitcoin ecosystem, the interaction experience on the Bitcoin blockchain was not user-friendly. It was jokingly said that whether a single chain’s technology could withstand the “attack” of inscriptions was a true test. User feedback highlighted issues such as slow transaction speeds and high costs. To get their inscriptions onto Bitcoin promptly, users were forced to learn how to modify the default Gas settings. Only then could their transactions be prioritized for inclusion in blocks. To address the issues of slow transactions and high fees, Unisat has introduced Fractal Bitcoin.

A Native Scaling Solution Based on the Bitcoin Mainnet

Fractals are a mathematical concept used to describe complex geometric shapes with self-similar properties. Self-similarity means that the structure of a part of the shape is similar to the structure of the whole, maintaining consistent features regardless of the scale at which it is observed. Fractal structures can be found widely in nature, such as snowflakes, coastlines, mountains, trees, and lightning paths.

In simple terms, a fractal is a special geometric shape that looks the same no matter how much it is magnified, like an infinitely repeating pattern.
Fractal Bitcoin uses the BTC core code to recursively create unlimited scaling layers on the BTC mainnet, enhancing transaction processing capacity and speed while maintaining full compatibility with the existing Bitcoin ecosystem. Fractal Bitcoin creates multiple scaling layers on top of the BTC mainnet, forming a tree-like recursive structure. This structure allows each layer to further expand in a “forking mode,” increasing the network’s parallel processing capacity.

Key Features and Implementation Process

The official introduction of Fractal highlights five main features: native, fast, dynamic scaling, consistent, and easy cross-chain transfers.

• Native: Fractal Bitcoin is developed using BTC core code with recursive scaling, ensuring consistent and unlimited scaling without relying on external structures, while supporting existing infrastructure (e.g., wallets).
• Fast: Block confirmation times on the Fractal network are about 30 seconds, with transaction processing capacity 20 times that of the BTC mainnet.
• Dynamic Scaling: On-chain interactions can dynamically scale up or down based on demand. Fractal acts as a dynamic “blockspace load balancer,” automatically adjusting the number of scaling layers based on network congestion. This makes internet-scale applications on the Bitcoin blockchain possible.
• Consistent: Due to the self-replicating consistency with the main chain, on-chain consensus is preserved. Transactions/hashes on any layer can be traced back to the source on the Bitcoin chain, without the risks of forks or shards.
• Easy: Thanks to consistency across layers, assets can be directly transferred from one layer to another without the need for additional relays.

How does Fractal Bitcoin maintain consistency with the Bitcoin mainnet while improving processing efficiency?

Multi-Layer Scaling Mechanism

Fractal utilizes the clever design of recursive scaling layers to increase BTC transaction throughput. Multiple levels of scaling layers are created on top of the BTC mainnet, forming a tree-like recursive structure. This structure allows each layer to expand further in a “forking mode,” increasing the entire network’s parallel processing capacity.
When the transaction volume on the main chain increases, Fractal automatically offloads some transactions to upper layers. Each layer can independently process transactions, and the number of scaling layers can dynamically increase or decrease based on network demand. During peak periods, new layers can be quickly created to handle surging transaction volumes. This dynamic scaling capability enables the network to flexibly handle varying loads, fully utilizing network resources.

Cadence Mining

Fractal adopts the same PoW consensus mechanism as Bitcoin, allowing BTC miners to seamlessly transition to Fractal block mining using their existing ASICs, GPUs, and other hardware. To diversify mining participation, Fractal introduces a combined mining mechanism called Cadence Mining, which merges permissionless mining and merge mining into a cycle of three blocks, where two blocks are generated through permissionless mining and one block through merge mining.
Simply put, permissionless mining allows anyone with the right tools and hardware to mine Fractal blocks, similar to BTC mining. Merge mining specifically targets BTC miners, enabling them to mine BTC and Fractal blocks simultaneously without requiring additional computational power.

Reintroducing OP_CAT

Fractal Bitcoin reintroduces OP_CAT, an opcode disabled in early BTC versions. OP_CAT allows two strings to be concatenated, and a script using OP_CAT can expand a 1-byte value into data exceeding 1 TB. This capacity to generate large amounts of data could be exploited by attackers for DoS attacks, leading to node crashes or network congestion. OP_CAT was disabled in early versions due to the lack of effective limitations on its potential for abuse until Tapscript limited stack elements to 520 bytes, effectively mitigating the risks.
Today, the OP_CAT opcode has become a powerful tool for developers, making it easier to handle large integers and enhancing BTC’s scripting capabilities. Reintroducing OP_CAT brings more development possibilities to the BTC ecosystem, with potential for on-chain applications, smart contracts, and more diverse on-chain adoption to take root on the BTC mainnet.

Conclusion

Bob Bodily, CEO of Bioniq, shared his thoughts on Fractal Bitcoin:

1. Fractal Bitcoin is a Bitcoin sidechain: It has its own miners and nodes, its own token, its own proof-of-work, and is completely independent of BTC. Compared to other BTC sidechains, Fractal Bitcoin combines the advantages of multiple BTC sidechains.
2. Limited smart contracts: Fractal Bitcoin does not add new opcodes to enhance smart contract functionality or introduce a virtual machine. Instead, it increases smart contract-like functionality by re-enabling OP_CAT.
3. Bitcoin bridge lacks innovation: The official documentation mentions an MPC-based bridge, which essentially relies on the same trust assumptions as multi-signature schemes.
   

Lorenzo, founder and CEO of Unisat, commented that Fractal is making rapid progress in implementing smart contracts and cross-chain bridges. Regarding smart contracts, Fractal introduced OP_CAT during the testnet reset and plans to enable it on the mainnet starting September 1st. This is the first step in enhancing Bitcoin scripting capabilities with the support of Unisat and the sCrypt team. Developers can explore potential programming capabilities enabled by OP_CAT on GitHub. Regarding cross-chain bridges, 3-5 methods for transferring assets from the Bitcoin mainnet to Fractal are in development, including both traditional and innovative approaches.

The Unisat team has been focused on building in the Bitcoin ecosystem long before the “inscription wave” exploded, and they continue to explore even as the Bitcoin ecosystem remains quiet. This shows the team’s long-term vision. Whether in terms of project philosophy or implementation mechanisms, Fractal Bitcoin indeed implements creative mechanisms to achieve native expansion of BTC. The broad adoption, long-term validation of security, and integration with the existing BTC ecosystem will require continuous iteration and time for testing. Whether the Unisat team and their products can spark a new “Bitcoin fever” remains to be seen.