What Is the CAT20 Standard & How Does It Work?
When the Ethereum (ETH) blockchain appeared on the horizon in 2015 with its smart contract functionality, non-fungible tokens (NFTs) and decentralized apps (DApps), many in the blockchain industry assumed that Bitcoin (BTC) would eventually fade into obscurity. The world's oldest blockchain simply didn't have any of the novel features that its younger rival boasted. Fast-forward to nearly a decade later, and several innovative protocols and token standards have ushered in the era of a totally new Bitcoin, one featuring its own NFTs, fungible tokens and even smart contractâlike functionality.
Over the past two years, the Bitcoin Ordinals protocol has enabled Bitcoin-based NFTs. The BRC-20 token standard, based on the same ordinal inscription theory, then introduced the ability to create fungible tokens on the chain. Soon afterward, the Runes protocol opened up a way to create fungible assets much more lightweight than BRC-20 tokens. With all of these innovations, it seems that Bitcoin has finally found its groove in the new blockchain world.
In September 2024, another potentially paradigm-changing token standard, CAT20, was proposed for the Bitcoin network. CAT20 allows developers to create Bitcoin-based fungible tokens that adhere to both the blockchain's native standards and the unspent transaction output (UTXO) model, while introducing high composability levels, creating opportunities for complex smart contractâlike functionality.
Key Takeaways:
CAT20 is a new proposed fungible token standard for Bitcoin. Among the advantages of CAT20 tokens are their ability to support relatively sophisticated composability, Bitcoin-level security, cross-chain interoperability and compatibility with the blockchain's UTXO transaction model.
CAT20 tokens can function on any chain supporting the OP_CAT opcode (operational code), which is currently disabled on Bitcoin. Discussions in the community are ongoing about whether OP_CAT should be re-enabled on the Bitcoin blockchain.
Introduction to CAT Protocol
CAT20 is a new proposed fungible token standard for the Bitcoin blockchain (CAT stands for Covenant Attested Token). The CAT20 token is:Â
based on Bitcoin's native UTXO transaction model
secured by a mining procedure
compliant with the blockchain's underlying security mechanism
In addition, the CAT20 token:
supports programmable mintingÂ
is designed to offer high levels of composability, a feature that paves the way for the use of smart contracts on the chainÂ
represents a new addition to the line of technologies and token standards recently proposed or introduced on Bitcoin to enable complex smart functionality and flexible fungible token operations
The standard was proposed in September 2024 by the CAT Protocol team, and is applicable to any blockchain that supports the OP_CAT opcode. Opcodes are special scripts that instruct blockchain transactions to perform certain operations. The Bitcoin blockchain supported the OP_CAT opcode until 2010, when the platform's anonymous founder, Satoshi Nakamoto, removed it due to security and transaction efficiency concerns.
Currently, there's a revived interest in OP_CAT within the Bitcoin user community, and several parties have proposed its reintroduction. If OP_CAT is re-enabled on Bitcoin, CAT20 will likely move from a proposed state to a fully implemented standard on the chain. Among the blockchain networks that currently support it is Fractal Bitcoin (FB), a Layer 2 sidechain solution that supports higher speeds and scalability levels for Bitcoin transactions.
The recently proposed CAT20 standard is not to be confused with the much earlier (and unrelated) CAT20 standard for compliant security tokens and tokenized securities, introduced in 2018 by the Securrency blockchain development outfit.
Understanding the CAT20 Standard
To understand CAT20 tokens, it's crucial to be aware of what the OP_CAT opcode does. Originally available on Bitcoin, it lets developers concatenate (hence the name) two pieces of data together, potentially opening a way to create complex transaction functionality. However, OP_CAT also has a certain potential to be exploited for running denial-of-service (DOS) attacks and congesting the Bitcoin network.
Due to these vulnerabilities, Satoshi Nakamoto disabled OP_CAT, along with several other opcodes. OP_CAT, which the CAT20 standard heavily relies on, still isnât functional on Bitcoin as of early October 2024. The primary rationale behind Nakamoto's decision probably lay in the desire at the time to keep Bitcoin strictly an environment for secure asset transfers and storage.
However, in the past few years, the blockchain has moved beyond its original state, with protocols and standards like BRC-20, Runes and Ordinals Inscriptions ushering in an era of a higher degree of network activity. Additionally, a variety of Bitcoin-linked Layer 2 solutions have contributed to the chain's ecosystem development.Â
With all of these technologies now fully operational on the Bitcoin network, many of its community members have questioned the need to keep OP_CAT disabled.
At the end of the day, if BRC-20 tokens are allowed to proliferate on the chain, and various Layer 2 protocols have introduced smart contract-like functionality for it, why would an exception be made for OP_CAT? Voices clamoring to re-enable OP_CAT are growing louder by the day, and there's an expectation that the opcode may be switched back on.Â
If and when that happens, CAT20 can support the creation and use of Bitcoin tokens with a significant degree of composability. Significantly, this could open up opportunities to leverage a variety of DApps within the Bitcoin ecosystem.
How Does the CAT20 Standard Affect the Bitcoin Blockchain?
Because CAT20 tokens are highly composable and modular, they could significantly increase the sophistication of Bitcoin transactions, potentially paving the way for full-fledged DApp functionality directly on the network.
At the same time, the ability to provide sophisticated functionality may lead to congestion on the network, due to the amount and complexity of operations these tokens are capable of producing. Bitcoin already struggles with the new standards and protocols â BRC-20, Runes and Ordinals Inscriptions â that have led to a large spike in activity on its network. The introduction of CAT20 tokens on the blockchain could further increase traffic levels.
Advantages of the CAT20 Standard
Bitcoin-Level Security
CAT20 tokens adhere to Bitcoin's underlying security mechanism, which is based on the proof of work (PoW) mining procedure. Itâs been instrumental in establishing the blockchain's reputation as a highly secure transactional environment. By leveraging PoW, CAT20 tokens would ensure that their operations are protected to the same level as native BTC assets.
Native to Bitcoin (UTXO-Based)
Besides PoW, another element that ensures Bitcoin's security is its well-regarded UTXO transaction model, whereby Bitcoin balances and transfers are represented by outputs from earlier transactions. CAT20 tokens are based on UTXO and directly leverage Bitcoin's own script at Layer 1. This means that these tokens don't need to rely on off-chain indexers â software used to organize transactions and simplify the querying of the blockchain.
Cross-Chain Interoperability
The CAT20 standard creates opportunities for cross-chain operations, as it can be implemented on any network that supports the OP_CAT opcode. We noted above that the Fractal Bitcoin Layer 2 sidechain is an example of a network with OP_CAT support. Besides Fractal Bitcoin, there are two notable Bitcoin forks with OP_CAT functionality enabled â Bitcoin Cash (BCH) and Bitcoin SV (BSV).
Lightweight
CAT20 tokens have built-in functionality to support simplified payment verification (SPV). This technology allows lightweight clients such as mobile phones to verify the authenticity of CAT20 tokens in a decentralized and efficient way.
Disadvantages of the CAT20 Standard
Limited to OP_CAT Networks
Although CAT20 holds certain potential for cross-chain interoperability, the existing network of chains that support OP_CAT (and which could thus theoretically support CAT20) is quite limited. The Fractal Bitcoin project is a new Layer 2 solution, still in the early stages of its market presence, while Bitcoin Cash and Bitcoin SV are minor players in the world of smart contractâcapable chains. These two platforms both support some degree of smart functionality using their own unique mechanisms.Â
Still, their DApp capabilities are far behind those of Ethereum and other smart contract chains, such as BNB Chain (BNB), Polygon (POL), Cardano (ADA) and Solana (SOL). As such, the token standard's potential reach is relatively restricted, especially since OP_CAT is still not operational on Bitcoin itself.
Potential Network Congestion
CAT20's ability to support complex, composable functionality can potentially lead to network congestion, due to both the large amount of processing required and the general increase in demand for DApps. Bitcoin already struggles with the issue of congestion, and the introduction of CAT20 might exacerbate this problem.Â
The chart below shows the number of Bitcoin transactions over the past three years (to Oct 6, 2024). Itâs impossible to miss the gradual rise in network activity over the previous year or so:
Early Stage Development
The CAT20 standard is still in the early stages of its development. Itâs been newly introduced and promoted by the CAT Protocol, and many practical details of its implementation have yet to be defined or made public.
Potential for Rising Fees
The rise in on-chain activity and DApp usage that CAT20 could spur would likely affect not only network congestion levels, but also transaction costs. Bitcoin is already facing increases in these costs, due to the flurry of activity related to BRC-20 tokens, Runes tokens and Ordinals Inscriptions NFTs. With the arrival of CAT20, the costs of transacting on Bitcoin may rise further.
CAT20 vs. Other Bitcoin Token Standards
CAT20 vs. BRC-20
CAT20 has a number of advantages over the BRC-20 fungible token standard. First, unlike BRC-20, CAT20 requires no off-chain indexers. With all of its operations conducted strictly on-chain, CAT20 tokens enjoy both higher efficiency and a better security profile than BRC-20 assets do. Additionally, CAT20 technology allows for far more flexible and sophisticated functionality than what the BRC-20 token standard can provide.
CAT20 vs. Runes
CAT20 tokens share certain similarities with Runes, another highly popular fungible token variety on Bitcoin. Both tokens largely leverage the on-chain environment for their functionality, although Runes does require indexers while CAT20 doesnât. Both standards can be lightweight, though in the case of CAT20 it largely depends upon the actual token design and intended functionality. In addition, both Runes and CAT20 tokens leverage Bitcoin's UTXO model.
However, the critical difference between these two token technologies is that CAT20 tokens can be used to enable fairly sophisticated DApps, ranging from automated money makers (AMMs) to lending and staking protocols. In contrast, the Runes protocol has mostly been confined to supporting meme coin issuance and use.
CAT20 vs. ARC-20
ARC-20 is a standard designed for fungible tokens that supports digital ownership management and asset representation for collectibles and NFTs. While ARC-20 is a fungible token standard, its main focus is on digital representation for distinct items and NFTs. In contrast, CAT20 is designed for fungible tokens with diverse applications and use cases.Â
While both token standards could potentially have use cases in decentralized finance (DeFi) or other DApp niches, CAT20 assets are capable of supporting more sophisticated and programmable functionalities.
The Future of the CAT20 Standard
As of the time of this writing Oct 8, 2024), the future of the CAT20 standard is highly dependent upon whether and when the OP_CAT opcode is re-enabled on Bitcoin. This will be determined by the overall Bitcoin community via online discussions and proposal deliberations. Unlike some chains with highly structured on-chain governance processes, Bitcoin has a flexible, mostly off-chain and less structured process of making decisions on matters as important as the reintroduction of critical opcodes.
CAT20 was proposed in September 2024 and active discussions are ongoing. It might take the Bitcoin community a few weeks or months to decide on this issue. Of course, there's always the possibility that OP_CATâs proposed reintroduction could either be rejected or left in limbo for an extended period.
The Bottom Line
The CAT20 standard is a significant step forward for Bitcoin, due to CAT20âs potential for relatively sophisticated programmability, reliance on Bitcoin's underlying security mechanism, UTXO-based nature and cross-chain interoperability. However, concerns about network congestion and rising transaction fees are running high within the Bitcoin community right now, primarily due to the avalanche of activity related to BRC-20, Runes and Ordinals Inscriptions.Â
Nevertheless, there's hope that the Bitcoin community is capable of distinguishing between technologies that are mostly suitable for meme coin acrobatics, and those that can provide useful DApp-like functionality. At the very least, the team at CAT Protocol hope so â and will be keeping their fingers crossed. If OP_CAT is re-enabled, expect CAT20 tokens to become a new hit on the world's largest blockchain network.
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