What is OP_CAT?
In a nutshell, OP_CAT takes the top two values from a script stack, joins them, and then puts the result back onto the stack.
This operation offers various scripting possibilities which was previously removed due to the risk of high memory consumption.
BIP 420 proposes to manage this risk by keeping the concatenated result within a 520-byte limit, and the changes would only apply to tapscript, specifically OP_SUCCESS126, and not on any other parts of the Bitcoin protocol.
Why Reintroduce OP_CAT?
The reintroduction of OP_CAT is believed to enhance Bitcoin’s scripting capabilities.
By allowing concatenation, developers could build more complex scripts that support advanced functionalities like multisig transactions.
The opcode could also play a role in enabling new cryptographic techniques to improve Bitcoin’s resilience against future threats.
A Soft Fork for Compatibility
BIP 420 suggests using a soft fork to reintroduce OP_CAT, which would keep the rest of the Bitcoin protocol unchanged. This approach is intended to maintain backward compatibility while allowing developers to experiment with the new functionality.
The Bitcoin community is discussing BIP 420, with varying opinions on its merits, with some developers seeing the potential for greater scripting flexibility, while others are concerned about security risks and network stability.
The proposal is ongoing, with no final decision made at this point.