Dealing with OP_IF and OP_NOTIF malleability

Summary:

The context discusses a BIP draft created by jl2012 for fixing malleability of transactions with OP_IF and OP_NOTIF. These codes are flow control codes in the Bitcoin script system that decide the programme flow based on whether the top stack value is 0 or not. However, this behavior opens a source of malleability as a third party may alter a non-zero flow control value to any other non-zero value without invalidating the transaction.As of November 2015, OP_IF and OP_NOTIF were not commonly used in the blockchain. However, as more sophisticated functions such as OP_CHECKLOCKTIMEVERITY are being introduced, OP_IF and OP_NOTIF will become more popular and the related malleability should be fixed. This proposal serves as a supplement to BIP62 and should be implemented with other malleability fixes together.If the transaction version is 3 or above, then the flow control value for OP_IF and OP_NOTIF must be either 0 or 1, or the transaction fails. This is a soft fork, and to ensure OP_IF and OP_NOTIF transactions created before the introduction of this BIP will still be accepted by the network, the new rules only apply to transactions of version 3 or above.For people who want to preserve the original behavior of OP_IF and OP_NOTIF, an OP_0NOTEQUAL could be used before the flow control code to transform any non-zero value to 1. A suggested modification was also provided wherein a script author could do something similar right now by prefacing his IF with a set of instructions that check whether the input is 0 or 1 and runs OP_RETURN if not.

Updated on: 2023-06-11T00:55:51.067341+00:00