Original Author: Jaleel 加六, BlockBeats

Earlier this year, I was writing "13 Lines of Code to Help BTC Implement Smart Contract? When reading OP_CAT soft fork, OP_CAT is still an unfamiliar term to many people. If it weren't for the BTC Non-fungible Token project Taproot Wizards to launch the Quantum Cat series Non-fungible Token with the help of meme culture to build momentum for OP_CAT, few people would probably know about this seemingly boring technical concept.

But just half a year later, OP_CAT is already hot and is even regarded as the next "Lighting Network". **The recently popular fractal network Fractal Bitcoin is actually the code implementation of OP_CAT in BTC, and Token FB has tripled or quadrupled within a few days of its launch. Therefore, in the BTC ecosystem, a number of OP_CAT-based protocols were born in just one day, such as CAT 20 on the fractal network, which also focuses on the concept of OP_CAT, and the GAS of the fractal network was once pulled to more than 5,000 in the days of mint, and the current price of a CAT is around 5.5 dollars over-the-counter, and there are even very few makers with a price, and the early mint people have achieved an increase of 5 to 20 times. And Quantum Cat has always been able to maintain a price of 0.25 BTC, becoming a blue chip of BTC Non-fungible Token.

It seems that as long as you get involved with OP_CAT, this thing can pump.

Not only the "self-esteem" of the community, but also the OP_CAT This technology is also very much discussed among BTC developers. I looked through this year's BTC Optech newsletter and BTC developer conference, and OP_CAT was a frequent visitor to the discussions.

Bitcoin Core developers Ethan Heilman and Armin Sabouri have jointly published a draft of the OP_CAT BTC BIP, which is now officially named BIP 347. Many of the biggest names in the BTC space, such as Tadge Dryja, author of the Lighting Network White Paper, Olaoluwa Osuntokun, CTO of Lightning Labs, the lead developer of Lighting Network, and Andrew Poelstra, head of research at Blockstream, have shown tremendous support for OP_CAT.

Why do Lighting Network developers favor OP_CAT?

To understand this phenomenon, we need to start with the Lighting Network. In 2011, Satoshi Nakamoto mentioned the prototype of the Lighting Network in an email, as a key solution for BTC scalability and payment speed improvement. Since its inception, the Lighting Network has attracted a large number of developers to follow.

In the past two years, the concept of 'BTC ecosystem' has been gaining momentum. Various BTC expansion solutions such as Sidechains and Virtual Machine have emerged one after another, attracting many investors. However, in the eyes of senior BTC developers, they are not considered mainstream and are difficult to enter the mainstream. After all, Lighting Network is currently the most outstanding 'payment channel' in BTC in the eyes of the public, and it is also one of the few 'legitimate sons' of Satoshi Nakamoto and the 'legitimate successor' of the BTC community spirit. Related reading: 'Seven years of forging a sword, the orthodox origin and challenges of the Lighting Network'.

However, the situation has changed dramatically in the past year. Several developers have announced their withdrawal from work related to the Lighting Network, and voices denying the Lighting Network have been heard one after another, especially from some senior developers. Fiatjaf, the founder of Nostr, was particularly outspoken: "The Lighting Network has been deceiving BTC users for as long as 6 years, consuming their time, energy, and money."

Against this background, some developers are looking for the next 'Lighting Network'. And OP_CAT is considered by many BTC developers to be the next major breakthrough for BTC after Lighting Network. Due to the technical nature of OP_CAT, let's first get to know those BTC developers who favor OP_CAT before discussing what OP_CAT is and what it can do.

BTC developers supporting OP_CAT

Lighting NetworkWhite PaperAuthor

Tadge Dryja is one of the authors of the Lighting NetworkWhite Paper, and in 2015 Tadge Dryja and Joseph Poon, another author of the Lighting NetworkWhite Paper, founded Lightning Labs under the leadership of Elizabeth Stark. The biggest difference between Lightning Labs and BlockStream, another BTCLighting Network company, is that Lightning Labs uses the Go programming language, while Blockstream uses the C programming language.

However, at the end of 2016, Tadge Dryja had disagreements and disputes with the Lightning Labs team, so he chose to leave when Lightning Labs was just one year old and instead joined the Digital Currency Initiative (DCI) at MIT to continue his research on the Lightning Network. At MIT DCI, he participated in multiple research projects, focusing mainly on the scalability and interoperability of cryptocurrencies and smart contracts. This includes the development of the Utreexo project, which is a new BTC scalability technology aimed at making BTC nodes smaller and faster. In 2022, Tadge Dryja joined Lightspark as a Senior Research Scientist. At Lightspark, he continues to address scalability issues with BTC and blockchain, utilizing his expertise as a co-inventor of the Lightning Network.

It is precisely because of his profound knowledge of BTCSmart Contract and scalability technology that Tadge Dryja has long recognized the potential of OP_CAT and has been supporting the testing of OP_CAT on the BTC test network and encouraging developers to try to 'break' OP_CAT to discover its potential problems. 01928374656574839201

Lightning Labs CTO

Olaoluwa Osuntokun (Roasbeef) is another co-founder and CTO of Lightning Labs, as well as an outstanding BTC developer who has made important contributions to the development of the Lighting Network. It can be said that the early team of Lightning Labs is no less competitive than Blockstream.

When it comes to Olaoluwa Osuntokun, it is impossible not to mention the 'gentleman's dispute' between him and Tadge Dryja. Interestingly, one of the main reasons Tadge Dryja left Lightning Labs was because of Olaoluwa. When Tadge Dryja was working at Lightning Labs, the initial version of the protocol he developed was called LIT, which was not compatible with BOLT, developed by Blockstream. However, Olaoluwa's development was compatible, gradually gaining recognition and favor from more developers. This eventually resulted in Olaoluwa surpassing Dryja to some extent, accelerating Dryja's departure.

However, history is always full of drama. Now, these two "archenemies" from Lightning Labs are currently working together to support OP_CAT.

Blockstream Research Director

There has always been a rumor among the public that Blockstream is the behind-the-scenes figure of BTC. Such rumors are not groundless. In 2014, Adam Back, the 'father of PoW,' gathered well-known early BTC developers such as Matt Corallo, Greg Maxwell, Pieter Wuille, and established Blockstream. They clearly took a stand and promoted the Lighting Network in the subsequent BTC scaling battle, giving Lighting Network its current status.

And currently, in the discussion about OP_CAT, Andrew Poelstra, the research director of Blockstream, is also an indispensable person. Andrew Poelstra is the research director of Blockstream and a senior BTC cryptographic script developer, whose influence in the industry is self-evident. As early as January 30, 2021, he wrote an article titled 'CAT and Schnorr Tricks I', discussing OP_CAT and pointing out that combining OP_CAT with CHECKSIGFROMSTACK can provide a clever method of transaction introspection.

Although Blockstream has not created a separate blockchain for OP_CAT, they have provided support for OP_CAT testing through the Bitcoin Inquisition, a test network for evaluating new BTC features. It's like building a secure "training ground" for OP_CAT, allowing researchers to carefully observe its performance under real-world conditions.

Andrew Poelstra also compared and discussed OP_CAT with other proposals such as OP_CTV, pointing out that OP_CAT provides more flexibility while OP_CTV focuses narrowly on non-recursive smart contracts.

Author of BIP 347

In the promotion of OP_CAT, BTC developers Ethan Heilman and Armin Sabouri have made significant contributions. They jointly wrote and promoted the proposal of OP_CAT, which has been officially designated as BIP 347. This proposal aims to redefine Operation Code OP_SUCCESS 126 through Soft Fork in order to re-enable OP_CAT.

Armin Sabouri has focused on the improvement of BTC script and consensus layer in the past. He believes that OP_CAT, while not the ultimate solution, provides the possibility for various new features and is an important step in the improvement of BTC script.

And Ethan Heilman is also the person who influenced Andrew Poelstra's thoughts. It was their private communication in the autumn of 2019 that changed Andrew Poelstra's original opinion on the so-called BTCSmart Contract functionality. Ethan Heilman pointed out that although people have concerns about the so-called BTCSmart Contract functionality, it can actually be achieved through CHECKMULTISIG, which is considered harmful for Smart Contracts. To prove this point, Ethan Heilman initiated a challenge on social media, encouraging people to propose feasible 'dark' Smart Contracts, but no one has succeeded so far.

StarkWare

StarkWare is a company that specializes in developing blockchain scaling technologies, particularly skilled in enhancing the privacy and efficiency of transactions using Zero-Knowledge Proofs (ZKPs). The company is committed to outsourcing complex computations from the mainchain (such as Ethereum) to secondary networks without sacrificing security and the characteristics of decentralization. In this way, StarkWare solves the scalability problem of blockchain while maintaining the transparency and verifiability of transactions.

StarkWare's drive to promote the activity of OP_CAT stems from its interest in the expansion of the BTC network and the functionality of Smart Contracts. OP_CAT is a BTC opcode that allows for the execution of more complex transactions and contracts on the BTC network through the concatenation of data. By enabling OP_CAT, StarkWare aims to achieve Smart Contract capabilities similar to those of Ethereum on BTC, thereby expanding the use cases of BTC and enhancing its functionality.

In July 2022, StarkWare launched a $1 million research fund specifically for studying the pros and cons of enabling OP_CAT on BTC. The fund aims to support researchers and developers who have innovative insights on how to safely and effectively implement OP_CAT on BTC.

In addition, StarkWare has also demonstrated the potential of using OP_CAT to achieve Zero-Knowledge Proof in the BTC test environment, especially on Signet. These works demonstrate how OP_CAT can be used to achieve more complex operations on the BTC network, such as the application of Zero-Knowledge Proof, which are key parts of Smart Contract functionality. Recently, StarkWare has also partnered with sCrypt to jointly explore the design of a PoC (Proof of Concept) bridge based on OP_CAT and ZK magic. It can be seen that StarkWare may also introduce an OP_CAT related protocol in the near future.

Others

The other few developers are not so famous, so let's put them together.

Salvatore Ingala has been deeply researching BTC payment pools and smart contracts, proposing a solution to optimize the payment pool exit process using OP_CAT, believing that this can significantly reduce on-chain data and operation costs. Ingala sees OP_CAT as a potential plugin for other BTC scaling strategies, such as Arc and Coinpools, and even future optimistic rollups for BTC, to improve efficiency and security.

Anthony Towns is one of the main developers of Bitcoin Inquisition, which is a more flexible tool similar to a test network used to test BTC protocol changes that have not yet been widely accepted. Towns promoted the activation of OP_CAT on the Inquisition platform, providing a secure "experimental field" for OP_CAT. Although Towns recognizes the importance of OP_CAT in testing new features and exploring the programmability of BTC scripts, he remains cautious about adding too much programmability to BTC, fearing that it may increase the risk of BTC being censored or controlled.

Robin Linus is the creator of BitVM. He believes that the reintroduction of OP_CAT provides a powerful tool for BTC, especially for projects like BitVM, which makes verifying arbitrary computation on BTC easier and more efficient. With the execution of OP_CAT, the BTC ecosystem is able to create more generic and expressive Smart Contracts, promoting a more functional and practical blockchain environment. Related reading: 'How do experienced developers view BitVM for computing anything on BTC?'

Why is the development of the Lighting Network so follow?

Developers of Lighting Network have shown such a strong interest in OP_CAT. What's behind this? To understand this, we need to first understand the essence of OP_CAT.

What is OP_CAT?

OP_CAT is an opcode in a BTC script that is used to stitch together pieces of data on two stacks into a larger element. Despite its deceptive simplicity, it provides more Smart Contract capabilities to the BTC network, allowing developers to create and process more complex data and transaction logic.

OP_CAT is not a completely new opcode, it first existed in earlier versions of BTC, but it was disabled in later versions due to security and complexity concerns. However, as BTC continues to grow, more and more developers believe that it is time to re-enable OP_CAT.

But why does such a seemingly simple operation trigger such a big discussion among BTC developers? One key reason is that it can significantly enhance the Smart Contract capabilities of the BTC network, allowing developers to achieve functions that are more complex or even impossible to achieve in the current BTC script.

The Potential Application of OP_CAT in Payments

OP_CAT has shown great potential in the payment system, especially in off-chain protocol and payment channel networks. Its reactivation will greatly improve the operational efficiency of these systems and reduce the burden of on-chain transactions. The main functions after the implementation of OP_CAT are:

Multi-signature (Multisig) optimization: In the Multi-signature scenario, OP_CAT can help users merge multiple signatures and combine them into a single data block, reducing the number of signatures that need to be submitted. This not only saves on-chain space but also reduces Money Laundering. Multi-signature is crucial for payment security and shared account management in BTC, especially in applications like Lighting Network, where OP_CAT makes this process more efficient.

State Contracts: OP_CAT can also be used for state contracts. This kind of contract is a form of Smart Contract that can maintain the state across multiple transactions, and through the OP_CAT, developers can stitch together the state information of different transactions to achieve more complex contract logic on BTC. For example, some complex payment protocols or distributed applications (such as lotteries, lotteries, or other complex financial products) need to maintain a certain state between multiple on-chain transactions, which can be achieved through OP_CAT.

Scalability of payment channel networks: Another important use case for OP_CAT is a payment channel network similar to the Lighting Network. In the payment channel network, users usually make a large number of micropayments on the off-chain, and only on the chain will they be on the chain when the final settlement is made. The splicing function of OP_CAT can make the intermediate transactions in the payment channel more effectively managed and verified. By stitching together different payment requests, users can perform more complex payment operations without increasing the burden on the on-chain. In this way, the throughput and efficiency of the payment channel can be significantly improved.

With the advancement of BIP 347 proposal, and more developers and researchers joining the exploration of OP_CAT, we have reason to believe that this once shelved opcode will bring new vitality to the BTC network. Just as Lighting Network went from concept to mainstream, the reactivation of OP_CAT could also be the next key milestone for BTC scaling and payment innovation.