The era of Bitcoin scaling has arrived
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The era of Bitcoin scaling has arrived
StarkWare has immense potential to demonstrate its capabilities in the Bitcoin OP_CAT era.
Navigating Web3 tides with focused insightsAuthor: Wilson Lee, Core Contributor at Biteye
Editor: Crush, Core Contributor at Biteye
01 Introduction
Bitcoin's inability to support general-purpose computation is a well-known limitation. Numerous early public blockchains, including Ethereum, were built to overcome this constraint and bring Turing-complete computing to blockchain, while Bitcoin has remained firmly positioned as "digital gold."
Following the surge in popularity of new Bitcoin-based assets such as inscriptions and runes, the market has recognized the immense potential of scaling "digital gold." A wide range of Bitcoin scaling solutions have since emerged, creating a thriving ecosystem. Among these, the proposal to restore OP_CAT has drawn significant attention.
With OP_CAT reinstated, STARK technology could enable zero-knowledge proof verification on Bitcoin, thereby introducing true general-purpose computation capabilities to the network.
In July this year, StarkWare launched a $1 million OP_CAT Research Fund aimed at advancing research into the benefits and risks of activating OP_CAT on Bitcoin. It is clear that StarkWare sees substantial potential to demonstrate its strength in a future Bitcoin era defined by OP_CAT.
02 The Past and Present of OP_CAT
The Removal of OP_CAT
OP_CAT was an opcode in Bitcoin’s scripting language designed to concatenate two elements on the stack into one. This functionality proved highly useful for constructing complex transaction scripts, enhancing script flexibility.
Bitcoin Script is a stack-based programming language where opcodes serve as fundamental low-level instructions. These opcodes execute functions such as conditional logic and signature verification, but offer limited computational capability.
Ethereum introduced the Ethereum Virtual Machine (EVM), significantly expanding blockchain computing power. The EVM enables developers to write arbitrarily complex smart contracts. Like Bitcoin, EVM relies on opcodes to issue basic computer instructions, but with far broader functionality.
The key distinction lies in purpose: Bitcoin’s opcodes are primarily used to validate transaction correctness, whereas Ethereum’s opcodes execute more complex logic. This difference allows Ethereum to achieve general-purpose computation, while Bitcoin remains computationally constrained.
Decentralization implies that computational resources are scarce and must be protected against malicious attacks such as denial-of-service (DoS). Ethereum addresses this via gas limits—each transaction consumes gas, and execution halts when gas runs out, preventing any single transaction from overwhelming the network with infinite computation.
OP_CAT, by enabling concatenation of stack elements, introduces greater logical complexity within individual computations. While this increases script flexibility, it also raises concerns about potential DoS vulnerabilities.
For security reasons, Satoshi Nakamoto removed OP_CAT from Bitcoin in 2010 to reduce the attack surface. This decision sacrificed some script expressiveness, especially in scenarios requiring data concatenation.
The Return of OP_CAT: Scaling and Controversy
As Bitcoin’s network evolved and demand for advanced features grew, the community began re-evaluating OP_CAT, recognizing its potential role in scaling solutions.
Discussions around reintroducing OP_CAT have intensified in recent years, particularly regarding its implications for Bitcoin scalability and smart contracts. Meanwhile, protocol upgrades like Taproot have alleviated earlier concerns about security and memory usage, leading to renewed calls for OP_CAT’s revival.
In October 2023, a proposal to restore OP_CAT by developers Ethan Heilman and Armin Sabouri gained widespread attention.
This proposal aims to reinstate the OP_CAT opcode through a soft fork, significantly enhancing the functionality of Bitcoin scripts—especially within Tapscript, the scripting language for Bitcoin’s Taproot transactions—enabling more sophisticated contract logic.
Amid the rising popularity of inscriptions and runes, discussions around OP_CAT became more formalized. Driven by community momentum, the OP_CAT proposal officially received BIP-420 designation (BIP stands for Bitcoin Improvement Proposal).
The designation was later updated to BIP-347. The primary goal of BIP-347 is to introduce more complex conditions—referred to as “covenants”—to enable advanced smart contracts, cross-chain bridges, and on-chain trading mechanisms. Covenant implementations could bring functionalities such as vault-like transactions, reversible payments, recurring payments, and complex financial instruments (e.g., escrow and bonds) to Bitcoin.
While OP_CAT offers promising benefits, it also presents challenges. Implementing this upgrade may increase Bitcoin’s complexity and introduce risks related to security and network forks. Additionally, some community members worry that new features could compromise Bitcoin’s simplicity and accessibility.
Thus, the impact of OP_CAT’s return requires ongoing discussion and exploration.
03 Why STARK?
STARK is a zero-knowledge proof system developed by StarkWare. Similar to the better-known SNARK, STARK scales systems by transforming the execution of complex programs into succinct, easily verifiable zero-knowledge proofs. This approach dramatically compresses the computational load of verifying large batches of transactions and enables rapid validation of their correctness.
Core Idea Behind Zero-Knowledge Proofs
The core idea of zero-knowledge proofs is to transform the result of a complex computation into a simple proposition that can be quickly verified, without requiring the verifier to re-execute the entire computation.
For example, suppose a complex computation takes seconds or even minutes to complete. The most straightforward way for a verifier to confirm its correctness would be to repeat the entire computation. However, by converting the process into a zero-knowledge proof, verification time can be reduced to milliseconds.
Technical Differences Between STARK and SNARK
The key distinction between STARK and SNARK lies in their underlying mathematical foundations—specifically, how they perform and verify zero-knowledge proofs.
SNARK primarily relies on elliptic curve pairings. While this method enables compact zero-knowledge proofs, it does not involve hash operations. Moreover, SNARK’s reliance on elliptic curve properties can limit its applicability in certain use cases.
In contrast, STARK is built entirely upon hash functions and polynomial commitments. Hash functions are cryptographic primitives widely used in blockchain systems like Bitcoin. They map inputs of arbitrary length to fixed-length outputs, offering both efficiency and strong security guarantees.
Compatibility: STARK and Bitcoin
Since Bitcoin itself is fundamentally built around hash computations, STARK’s computational model aligns closely with Bitcoin’s native operations.
STARK’s reliance on hashing allows it to integrate directly with Bitcoin’s existing cryptographic logic. This compatibility means STARK can implement zero-knowledge proofs on Bitcoin more efficiently, without requiring major changes to Bitcoin’s current execution model.
Why OP_CAT Is a Prerequisite?
OP_CAT enables the concatenation of stack elements—a critical requirement for building complex zero-knowledge proof verification scripts. With OP_CAT, Bitcoin scripts can flexibly combine multiple data segments, supporting more intricate logical structures during verification. This makes the integration of STARK feasible, as OP_CAT provides the necessary scripting capabilities to verify STARK proofs.
More specifically, restoring OP_CAT would allow Bitcoin to support the complex data operations required by STARK proofs—such as concatenation, validation, and iterative processing. These operations are essential in both generating and verifying zero-knowledge proofs. By enabling OP_CAT, Bitcoin can maintain high verification efficiency and security without introducing Turing completeness, thus paving the way for STARK adoption on the network.
04 Conclusion and Outlook
Bitcoin scaling has emerged as a central theme in the industry, playing a vital role in sustainable development. On this front, StarkWare has demonstrated exceptional innovation, leveraging its leadership in zero-knowledge proofs and scaling technologies.
However, the successful application of STARK still depends on further advancements such as the activation of OP_CAT. We look forward to continued efforts and exploration by technical teams across the ecosystem, collectively driving the evolution of Bitcoin’s infrastructure.
Looking ahead, with the potential restoration of OP_CAT, StarkWare is poised to shine in this new era, further solidifying its leading position in blockchain scaling. We are optimistic about StarkWare’s potential to advance Bitcoin scaling and enhance network performance, and we anticipate that they will deliver further breakthroughs and innovations in blockchain technology.
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