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I have a new BIP draft for fixing OP_IF and OP_NOTIF malleability.
Please comment:
https://github.com/jl2012/bips/blob/master/opifmalleability.mediawiki
Copied below:
BIP: x
Title: Dealing with OP_IF and OP_NOTIF malleability
Author: jl2012 <jl2012@xbt.hk>
Status: Draft
Type: Standards Track
Created: 2015-11-06
Abstract
As an supplement to BIP62, this document specifies proposed changes to
the Bitcoin transaction validity rules in order to make malleability of
transactions with OP_IF and OP_NOTIF impossible.
Motivation
OP_IF and OP_NOTIF are flow control codes in the Bitcoin script system.
The programme flow is decided by whether the top stake 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 are 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.
Specification
If the transaction version is 3 or above, the flow control value for
OP_IF and OP_NOTIF must be either 0 or 1, or the transaction fails.
This is to be implemented with BIP62.
Compatibility
This is a softfork. To ensure OP_IF and OP_NOTIF transactions created
before the introduction of this BIP will still be accpeted by the
network, the new rules only apply to transactions of version 3 or above.
For people who want to preserve the original behaviour 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.
Reference
BIP62: https://github.com/bitcoin/bips/blob/master/bip-0062.mediawiki
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