OP_CAT: The Key to Bitcoin’s Future Dominance?

Bitpush News
4 min readJan 22, 2024

Bitcoin is in the midst of a cultural revolution. Since the introduction of ordinal theory, allowing for tokens and NFTs natively on the Bitcoin blockchain, new schools of thought have emerged about expanding Bitcoin and allowing it to become a layer of global settlement and digital activity. To expand this vision further, some suggest re-introducing the OP_CAT opcode, which could allow for smart contract-like features and trustless bridges to L2s. Let’s explore the history of OP_CAT, its recent surge in popularity driven by the Taproot Wizards, and what its future could be.

OP_CAT is an opcode that was introduced to Bitcoin very early in its existence by anonymous creator Satoshi Nakamoto. Opcodes in Bitcoin’s scripting language allow for basic data manipulation and transaction management and can be considered the building blocks for Bitcoin’s extremely basic programming language. The “CAT” in OP_CAT is short for concatenation, as the opcode allowed for concatenating the two items at the top of Bitcoin’s scripting stack, or place for storing data, into one.

OP_CAT was removed from Bitcoin around 2010 because of potential concerns surrounding exploits that could be done by repeatedly duplicating and concatenating the items at the top of the list, which would overflow Bitcoin clients. To ensure that this would not happen, Satoshi not only removed OP_CAT but also reduced the number of opcode calls per transaction and introduced a stack size limit.

With the renewed interest in expanding Bitcoin beyond a simple peer-to-peer electronic cash, interest in OP_CAT has been revived. The Taproot Wizards, a group led by Eric Wall and Udi Wertheimer whose goal is to “Make Bitcoin Magical Again” by incentivizing technological developments, have led the OP_CAT revival effort. Earlier this month, they announced their Quantum Cats Ordinals project — a collection of 3,333 cat images that can evolve and change appearance over time. The goal of the collection is to bring more awareness to OP_CAT and create a community of thousands of enthusiasts who can vouch for the revival of OP_CAT as an opcode.

The concept of bringing together NFTs into a community social movement is genius. Due to the project’s association with the opcode, Cats holders are directly incentivized to push for greater adoption of OP_CAT. At the same time, a successful OP_CAT implementation will be primarily attributed to this project, which will increase its community value and potentially its price.

If OP_CAT were to be reintroduced to the Bitcoin protocol, several novel innovations would now be possible. Most significantly, a trustless bridge could be made between Bitcoin and a zero-knowledge Layer 2, allowing for a cryptographically secure smart contract ecosystem to flourish on the Bitcoin blockchain, with all the same guarantees that mainnet Bitcoin provides. OP_CAT could also allow for post-quantum signatures on Bitcoin, called Lamport Signatures. Another useful feature would be covenants, which restrict how Bitcoins can be used after sending them and could create multi-signature vaults among other interesting wallet management techniques.

Reintroducing OP_CAT to Bitcoin is long and arduous, as numerous obstacles exist to overcome. Some of the biggest hurdles include creating the BIP (Bitcoin Improvement Proposal), writing the OP_CAT code, waiting for it to be included in Bitcoin clients, and getting miners to adopt it. Only after all of this can OP_CAT begin to demonstrate its usefulness. Whether or not it passes all of these steps remains to be seen, but one thing is for sure: Bitcoin is becoming so much more than just digital cash, and thought leaders in the space are deadset on preventing it from falling into obscurity.

By Lincoln Murr

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