What, why and how OP_CAT?
OP_CAT is one of a number of opcodes within the Bitcoin scripting language. You Are El does a fantastic job of explaining it here.
In Bitcoin's scripting language, OP_CAT is used for concatenating two strings or data elements. In multi-signature scenarios, these elements are typically the public keys and signatures required for transaction authorization. OP_CAT's ability to merge these elements is essential for forming the complex script conditions. But where do Quantum Cats fit in? Udi breaks it down, including the massive progress made here.
Benefits Of OP_CAT
Enhanced Scripting
Seamlessly concatenate values on Bitcoin's blockchain for more complex & versatile scripts.
Flexible Transactions
Enable dynamic transaction structures and multi-condition smart contracts with ease.
Quantum Resistance
Facilitate post-quantum cryptographic methods like Lamport Signatures for future-proof security.
What we are saying about OP_CAT?
Application of OP_CAT for Multi-Sig Wallets
Multi-signature wallets are the digital equivalent to a multi-key safe. They require the consent of multiple key holders to authorize transactions. This system is essential for businesses aiming to use bitcoin and its network to manage their internal financial system. Multi-signature authorization for business transactions is very common in traditional business settings, where financial governance demands checks and balances.
In the context of Bitcoin, these wallets are already supported natively through the OP_CHECKMULTISIG opcode, which allows transactions to require multiple signatures for validation.
Currently, Bitcoin's native multi-sig capabilities, while functional, are somewhat limited in flexibility, leading businesses to rely on third-party solutions, which has the potential to introduce security risks. This demonstration shows how OP_CAT can be used to enhance Bitcoin's native multi-signature capabilities. OP_CAT reintroduces flexibility to Bitcoin scripting allowing for more dynamic script conditions than the current OP_CHECKMULTISIG.
Basic Bitcoin Multi-Signature Transaction Using OP_CHECKMULTISIG
In a simple 2-of-3 multi-sig setup using OP_CHECKMULTISIG, the Bitcoin script requires any two out of three possible signatures to validate a transaction.
Here's a pseudo-code representation:
// Pseudo-code for a basic 2-of-3
// multi-sig transaction using OP_CHECKMULTISIG
<Public Key A>
<Public Key B>
<Public Key C>
3
<Signature A>
<Signature B>
2
OP_CHECKMULTISIG
In this setup, the transaction is authorized if any two out of the three signatures (Signature A, Signature B, Signature C) are provided. If we wanted to augment the functionality so that if a business requires a more complex setup:
// High-value transaction script (pre-defined)
<Public Key CFO> <Public Key CEO> 2
<Signature CFO> <Signature CEO> 2
CHECKMULTISIG
// Routine transaction script (pre-defined)
<Public Key Manager> <Public Key Accountant> 2
<Signature Manager> <Signature Accountant> 2
CHECKMULTISIG
In this setup, each type of transaction requires a separate, pre-defined script. Dynamic changes based on transaction conditions or hierarchical updates aren't feasible. The multi-sig wallets need to be predefined with a fixed set of keys, and any changes in the authorization structure would require creating a new wallet or script. There's no native capability to dynamically alter the set of keys or signatures involved in a transaction based on varying conditions.
Enhanced Multi-Signature Transaction Using OP_CAT
Now, let's consider a more complex scenario where a business needs a flexible multi-sig setup. For example, a company might require different combinations of signatures based on transaction types or amounts. Here, OP_CAT can dynamically assemble these signature combinations. Furthermore, as a business evolves, this script needs to be dynamic as transaction conditions or hierarchical changes occur within the organization.
// Check if the transaction is high-value
OP_IF
// Concatenate CFO's and CEO's keys
// and signatures for high-value transactions
<Public Key CFO> <Signature CFO> OP_CAT
<Public Key CEO> <Signature CEO> OP_CAT
2 CHECKMULTISIG
OP_ELSE
// Concatenate Manager's and Accountant's
// keys and signatures for routine transactions
<Public Key Manager> <Signature Manager> OP_CAT
<Public Key Accountant> <Signature Accountant> OP_CAT
2 CHECKMULTISIG
OP_ENDIF
In this enhanced script:
- For high-value transactions, signatures from both the CFO and CEO are required.
- For routine transactions, signatures from a manager and an accountant suffice.
OP_CAT hypothetically enables the dynamic injection of public keys and signatures into a script. This means you could create scripts that adapt to changes in signature requirements based on specific conditions, like different levels of transaction amounts or changes in the authorization hierarchy. It essentially allows for the on-the-fly construction of multi-signature conditions.
Demo of OP_CAT MultiSig
Below you can test out this simulation of OP_CAT based MultiSig wallets. In this example, you can see how we can dynamically inject conditions for what approvals are required to sucessfully process a transaction.
Current Threshold: 0.05 BTC
TX Status
Other Potential Applications
Bitstream Protocol Implementation
A Bitstream Protocol model enabling Bitcoin-paid decentralized file hosting through atomic swaps for decryption keys.
Tree Signature
Simulation
A simplified model of a multisignature script using tree signatures, which can encode complex spending conditions.
Vaults with Enhanced Security
Constructing Bitcoin vaults that prevent a malicious party from accessing funds even if they have the private key.
Community Voices
Where is our OP_CAT?
Resources
Checkout some other great resources about OP_CAT to learn more about it:
- Quantum Cats
- Taproot Wizards
- Quantum Cats - Genesis Cat Southeby's Auction