Bitcoin network upgrades are quite rare — the last Taproot soft fork was activated in November 2021. For comparison: since that moment, Shapella, Dencun and The Merge have been updated in Ethereum, and a Pectra upgrade is already planned for the first quarter of 2025.
Meanwhile, the community is only discussing the possibility of implementing a bitcoin improvement proposal called OP_CAT (BIP-347). We tell you why it is interesting and why the ideas of the developers are being implemented so slowly.
To remove, it is impossible to add
Shortly before the disappearance in 2010, bitcoin creator Satoshi Nakamoto made several significant changes to the protocol of the first cryptocurrency:
introduced a 1 MB block size limit to prevent spam attacks and improve network decentralization;fixed errors related to integer overflow, which could lead to the creation of incorrect or malicious transactions;removed centralized nodes by adding a DNS seed mechanism that allows clients to dynamically find nodes to connect to the network;disabled 16 opcodes, including OP_CAT. The latter puts a single-byte value on the stack, and then repeats OP_DUP and OP_CAT 40 times, increasing it to more than 1TB.These innovations have ensured the development of digital gold while maintaining decentralization. Nevertheless, the features of the Script language had a negative impact on the programmability of bitcoin:
stack language. Operations are processed in a stack that operates on the principle of "last in, first out" (LIFO);incomplete in Turing. It does not support loops and other constructions that can lead to endless calculations. This limits the creation of dapps with complex smart contracts, but makes the language more secure.;a small set of commands. The limited number of opcodes allows you to perform only simple operations such as adding, comparing, and hashing data on the stack.At the end of 2021, the Taproot soft fork occurred on the bitcoin network, which included support for Schnorr signatures (BIP-340) and the TapScript script encoding language (BIP-342). The latter limited the maximum size of the stack element to 520 bytes, which means it eliminated the potential vulnerability of OP_CAT.
You can't remove it, add it
The draft of BIP-347 was published by programmers Ethan Heilman and Armin Saburi in 2023. They suggested restarting OP_CAT as a soft fork by adding its code to the existing OP_SUCCESS126 operation.
Smart contracts (SC) allow you to transfer funds automatically and without intermediaries. However, in bitcoin, their functionality is limited to locking and unlocking.
Covenants — conditions or restrictions that ensure the fulfillment of certain rules when interacting with assets or functions described in the contract - can expand the capabilities of the IC in the network of the first cryptocurrency.
The main function of OP_CAT is concatenation, combining two or more strings or other sequences into one. The developers of BIP-347 propose using reverse concatenation to create recursive covenants and divide stack elements into several parts.
If the smart contract receives a signature and a public key from the user, he will be able to verify them independently, ensuring that both elements relate to the same transaction.
The implementation of OP_CAT will minimize the threat from quantum computers, as well as implement bitcoin on the network:
storage — covenants for blocking intruders who have gained access to the user's secret key;multi-signatures with more than 20 public keys thanks to the use of Merkle trees when checking scripts;secure cross-chain bridges with L2 networks;support for complex financial instruments such as escrow accounts;advanced features for atomic swaps;penalties for double spending in payment channels.Taproot Wizards co-founders Eric Wall and Udi Wertheimer led a PR campaign to bring back OP_CAT under the slogan BIP-420 and created a collection of Quantum Cats "inscriptions", focusing on increasing the quantum stability of bitcoin after the update.
The Quantum Cats collection. Data: Magic Eden.According to CoinGecko, in April 2024, the minimum price of a "quantum cat" reached 0.47 BTC. At the time of publication, NFTs are trading at 0.28 BTC.
OP_CAT is not the only covenant support offer. The developers have proposed several other approaches:
Check Template Verify (CTV) is an opcode from Jeremy Rubin that ensures that only transactions matching a predefined template can spend coins. Possible storage cases and more complex multi—signature schemes;OP_CHECKSIGFROMSTACK (CSFS) facilitates the creation of multi—signatures - it allows you to check them by extracting them from the stack, rather than from standard transaction fields. It is considered a more flexible and powerful solution for implementing an expanded range of applications;LNHANCE. It offers flexible scripting capabilities, including loops and conditional execution based on external data. A conceptual and less formalized proposal.The community is also discussing the implementation of cross-chain bridges and L2 networks in the case of OP_CAT implementation. For example, Taproot Wizards has started developing a protocol for scaling Bitcoin CatVM as an alternative to the existing BitVM solution, where users have to rely on operators to transfer funds.
The StarkWare company behind StarkNet has announced its intention to make the L2 network a single level of scaling for the first cryptocurrency. According to the co-founder of the company, Eli Ben-Sasson, this can be achieved six months after the implementation of OP_CAT:
"As soon as OP_CAT is accepted, the implementation of the STARK verifier into the bitcoin script will become a reality. This will open the way for safe and independent movement between the blockchain of the first cryptocurrency and StarkNet, creating a single level of scaling for both Ethereum and BTC."
Why so long
Bitokin is an open protocol that allows anyone with the necessary skills to publish BIP. However, after that, the proposal must be approved by a group of editors, and then approved by 95% of miners.
The BIP life cycle. Data: Forklog.For a long time, the only editor of BIP was Luke Dash Jr., who expressed an ambiguous opinion about the future of the first cryptocurrency. For example, at the beginning of the year, he proposed blocking Ordinals at the code level, but did not receive enough support.
In April 2024, Bitcoin Core programmer Ava Chow proposed forming a group of editors to speed up the decision—making process and remove excessive responsibility from Luke Dash Jr.
The team includes bitcoin developers Brian Bishop (Kanzure) and John Etak, participants bitdevs.org Mark Erhardt (Murch) and Ruben Somsen, as well as Lightning Labs CTO Olaoluwa Osuntokun (Roasbeef).
Ava Chow introduces the new BIP editors. Data: gnusha.org .The innovation made it possible to accelerate the next possible upgrade: on April 24, 2024, the editors assigned OP_CAT the number BIP-347.
"Assigning a number does not signal consensus in the community, but makes it easier to discuss and write software for a proposal, because now it has a unique identifier that everyone agrees with," Ethan Heilman said in an interview with CoinDesk.
Conclusions
OP_CAT will expand the functionality of bitcoin and allow you to create advanced smart contracts in the network of the first cryptocurrency.
The path from the first mention to the implementation for SegWit and Taproot updates took about two years, and the activation itself took place a year after community approval. Given this experience, we can expect the introduction of BIP-347 in 2026.