Taproot Wizards, the group behind Bitcoin inscriptions, wants to revive an old idea first implemented by Bitcoin’s creator in its early days.
A bit of code — an opcode, short for “operation code” — known as OP_CAT was part of Bitcoin’s original scripting system and was used to concatenate (hence the “CAT”) two strings.
You can think of an opcode as a step in a recipe, like “chop the onions” or “boil water.” It tells the computer (or in this case, the Bitcoin network) what to do with the data it has. For example, an opcode might tell the network to add two numbers together, check if one number is larger than another, or combine two pieces of data.
Each opcode is a basic building block that, when combined with others, creates the complex rules and conditions for how transactions operate on the blockchain. Many opcodes remain active from that time period.
Several opcodes, including OP_CAT, were disabled by Satoshi Nakamoto in 2010, over concerns about potential vulnerabilities affecting the young and fragile network. Satoshi worried it might be used to launch a denial-of-service (DoS) attack, for instance.
But Udi Wertheimer of the Taproot Wizards, which promotes Ordinals, thinks it’s high time this particular opcode was reinstated.
“It’s not a full-blown smart contracting language like on Ethereum or Solana, but it does enable a lot of functionality that we couldn’t do before,” Wertheimer told Blockworks, citing decentralized exchanges and bridging assets as examples.
Unlike Ethereum, Bitcoin’s programmability was intentionally limited, to keep it simple and secure.
Re-enabling OP_CAT, however, is a relatively simple change to Bitcoin Core code, involving only around 10 lines of code, Wertheimer said.
Bitcoin is notoriously difficult to change, governed by a slow moving consensus process among a few dozen developers who update the software, which then must be adopted by the thousands of full nodes, including miners, to take effect.
One advantage of OP_CAT, like another recent proposal to expand Bitcoin’s utility, BitVM, is that it would not require a hard fork — the most contentious type of change. Instead, OP_CAT would need only a soft fork, which requires less coordination among stakeholders. The last one occurred in 2021, with the activation of Taproot, which made Ordinals possible.
Read more: Bitcoin research expands on design space for smart contracts
“[OP_CAT] actually enables bridging which — I think even [BitVM proponent] Robin Linus would agree — without some sort of soft fork, BitVM in practice would be difficult to use,” Wertheimer said.
BitVM doesn’t necessarily require any sort of fork but Wertheimer said Linus is a supporter of OP_CAT, because it can make it easier to accomplish his own project’s goals.
Some Bitcoin forks, such as Bitcoin Cash, have re-enabled OP_CAT already. As part of a broader effort to increase the script capabilities of Bitcoin Cash, developers brought back the opcode in May 2018.
Some of the uses of OP_CAT in Bitcoin Cash involve the creation and management of tokens, payment channels, and methods for embedding and retrieving data on the blockchain.
The opcode is also enabled on Blockstream’s Liquid side chain, where it facilitates decentralized token exchange.
Quantum Cats
Unlike some blockchain networks’ NFTs, which consist of metadata pointing to off-chain assets, inscriptions on Bitcoin are fully on-chain and immutable. But that doesn’t mean they have to be static.
Taproot Wizards set out to create “evolving inscriptions,” which are pre-programmed to reveal new characteristics progressively.
Quantum Cats is a limited edition set of 3,333 cat images, revealed in full on Friday after being minted in a mysteriously expensive transaction last week.
The full collection was revealed on Friday. The encrypted data is what will allow the images to change over time — Wertheimer said there would be “a bunch” of changes but declined to say how many could be expected or to specify the timeline.
“The process of making it was really fun because we had to try to anticipate what was going to happen — because once we put it in there, we can’t touch it anymore,” he explained.
The first, a 1-of-1 “Genesis Cat” by Taproot Wizards artist “FAR” will be sold at auction by Sotheby’s starting today through Jan. 22.
It’s essentially a marketing campaign for the work of Bitcoin developers.
“I think that can bring a lot of attention and basically celebrate the fact that there are developers who’ve been working on OP_CAT and perfecting it for the last five years, and people barely know about it,” Wertheimer said. “The behind the scenes work is very technical, very political, and it’s very hard for people to get exposure to what’s really going on.”
By contrast, Ethereum developers plan, debate, code and upgrade the chain fully in public, with major features like EIP-1559, the Merge and Proto-Danksharding promoted to great fanfare.
Taproot Wizards want to bring a similar rallying energy to Bitcoin improvements.
“I know a lot of people think that Bitcoin shouldn’t change,” said Wertheimer. “I think Bitcoin should be very slow to change and very careful, very deliberate to change.”
Bitcoin is still too young to fully ossify, he argues, lamenting that the governance process is “somewhat broken.”
“Almost the entire technical community is in agreement that there will be more upgrades, but there is difficulty in figuring out which ones,” he said.
But change is necessary.
“Bitcoin as it is today just cannot yet serve billions of people.”
Correction Jan. 12 at 10:58 am ET: Software developer Casey Rodarmor introduced the idea of “ordinals” in early 2023.
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