One more brick and Bitcoin could change permanently in 2025

Today, the main development problem of the Bitcoin protocol seems to be modular. By this I mean that the shape and changes that its protocol will undergo in 2025 depend on the implementation or rejection of a single programmability capability or function in Bitcoin. These changes could be large, significant and affect the currency’s network forever. .

In 2025, Bitcoin could see a rapid transformation, perhaps greater than usual, if developers decide to modernize and “accelerate” the protocol by implementing covenants, ZK-rollups and layer 2 solutions, all of which would be possible through a single opcode: OP_CAT. This is a programming code in Bitcoin Script which allows two values ​​to be concatenated into a single stack of code.

OP_CAT was implemented by Satoshi Nakamoto, the creator of Bitcoin, and later removed from his scripts in 2010, after an event known as value overflow incidentor value overflow incident.

Said incident It allowed the creation of more than 184 billion bitcoins that did not exist. This amount far exceeded the fixed supply of 21 million BTC. The devaluation episode was resolved by rejecting the overflow of value by publishing a new version of the bitcoin client, which had the effect of a soft fork in the network’s consensus rules.

Today, this opcode is in effect again, but as a proposal in the Bitcoin development repository with the identifier BEEP: 347. That is, it has been rescued from the past (and promises to be important for the future) due to the functionalities that it would add to the protocol of the most important crypto asset in the world.

Why OP_CAT?

According to the proposal repository, Bitcoin scripts, specifically the Tapscript extension of this programming language, They lack a general-purpose way to combine objects across code stacks, which places limitations on the programmability of the protocol.

The absence of this technical capability restricts the expressiveness and power of Tapscript. This prevents, among many other things, the ability to build and evaluate Merkle trees and other hash data structures in Tapscript. OP_CAT, by adding a general-purpose way to concatenate values ​​from the stack, would overcome this limitation and greatly increase the functionality of Tapscript.

Github, BIP 347.

It is said that the future of Bitcoin development is modular because the mere integration of OP_CAT would allow a considerable expansion of its protocol.

Below is a list of use cases that include this opcode would allow:

Bitcoin to pay for information natively

Bitstream is a protocol that allows payment with bitcoin to data and file hosting servers. While this protocol could be implemented without OP_CAT, the inclusion of this opcode simplifies the process and resources, eliminating the need for more complex technical solutions.

An atomic coin exchange [bitcoin] by files would allow an open market for content hosting, in which anyone can monetize their excess bandwidth and data storage capabilities, offering decentralized multimedia services.

Bitstream Whitepaperdata hosting server.

This means that OP_CAT would allow decentralized distributors of multimedia content to be paid directly through the Bitcoin chain. BTC, then, would expand its use cases, specifically its reach as a means of payment on the internet.

Tree signatures for advanced multi-signature transactions

Tree signatures allow more flexible spending conditions, especially in multi-signature conditions. They allow designing more complex conditional charges than the traditional “n-of-m” used by current multi-signature transactions, where “n” is the number of signatures required and “m” is the total number of keys.

According to the Bitcoin proposal repository, tree signatures allow “a transaction less than 1 KB in size could support tree signatures with up to 4,294,967,296 public keys.” Therefore, they contain many public keys without requiring transactions to take up much space.

Protection against quantum attacks

The Lamport signaturesa system of one-time keys, can theoretically protect bitcoin against quantum attacks. It is clear that these attacks will be possible in the future, especially now that the first stone has been laid in the building of commercial quantum technology: Google’s Willow chip.

A specialist says that for Lamport signatures to be able to protect Bitcoin from quantum processing, the introduction of OP_CAT is required.

If we required that the ECDSA signature be signed with a quantum-proof signature algorithm, then we would have a quantum-proof Bitcoin. And the 5-byte signature scheme we discussed earlier is a Lamport signature, which is quantum-safe. Unfortunately, we need at least 20 contiguous bytes… so we need some kind of operation similar to OP_CAT.

Jeremy Rubin, Bitcoin developer.

ECDSA means Elliptic Curve Digital Signature Algorithmwhich translates to elliptic curve digital signature algorithm. Simply put, it is defined as the method used by Bitcoin to generate digital signatures and verify their authenticity and integrity, all of which helps protect bitcoiners’ keys.

The security of ECDSA, which is based on the difficulty of solving the mathematical problem of the private key from the public key (elliptic discrete logarithm problem), is practically invulnerable against the computing power of current computers. Quantum computers, however, could defeat it, which is why a quantum-processing-proof algorithm is needed.

Punish Bitcoin Double Spending Attempt

Non-equivocal contracts serve to prevent and punish double spending in second layers or sidechains (sidechains) of Bitcoin. Avoiding double spending in the digital payment system is important because the proliferation of these, and even just one, can lead to a loss of confidence in the electronic system.

These contracts can be used using the Tapscript language, but using OP_CAT, since this opcode applies “rules on the nonce [números únicos utilizados una vez] of the expense transaction. Since bitcoin already has ways to prevent double spending from happening on its main network, This technological advance would especially affect payment channels.

Bitcoin’s new lines of defense

The vaults are specialized contracts that protect a user’s funds from theft, even if the user you lose your private key, which has historically been considered the last line of defense in Bitcoin self-custody.

Using OP_CAT, Bitcoin scripts can use covenantssmart contracts that restrict how bitcoins can be spent. These covenants are necessary to design vaults that allow attackers to be expelled from the fraudulent possession of funds.

Vaults are an attractive key and access backup option for many developers who see traditional custody of a single private key as a point of failure in large-scale bitcoin adoption.

Is there a secondary interest in OP_CAT?

The discussion about OP_CAT, which would bring all the mentioned possibilities among many others, has been lively in recent years, especially in 2023.

The reason it is again at the center of the debate is that its reintegration would allow smart contracts to be created in bitcoin. That’s right: part of the developer community envisions a future where Bitcoin has functionalities similar to Ethereum, even if OP_CAT aims to improve the conservative core of Bitcoin’s technical section.

With OP_CAT, it is plausible that Bitcoin, in addition to being a payment network, also functions as a layer of applications and businesses over the Internet. That would allow many businesses and Internet companies capture a significant market share of one of the most important assets in the world.

Of course, not all developers agree with this fate for Bitcoin. Some consider OP_CAT to open the door to bugs and security vulnerabilities, and would prefer that Bitcoin remain a conservative network, specializing in monetary value transfers.

Finally, it is not ruled out that the Bitcoin development community creates a technical solution that does not require forking the network to add smart contracts and other advanced functions, which would represent a middle point between conservative and progressive Bitcoiners.