From: Luke Dashjr <luke@dashjr.org>
To: bitcoin-dev@lists.linuxfoundation.org,
	Christian Decker <decker.christian@gmail.com>
Date: Wed, 21 Oct 2015 06:18:54 +0000
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Message-Id: <201510210618.56159.luke@dashjr.org>
Subject: Re: [bitcoin-dev] [BIP] Normalized transaction IDs
Precedence: list

On Monday, October 19, 2015 2:01:04 PM Christian Decker via bitcoin-dev wrote:
> The proposal is implemented (see below), by computing the normalized
> transaction ID when adding them to the UTXO and storing them along with the
> coin state. OP_CHECKSIGEX mostly duplicates OP_CHECKSIG and
> OP_CHECKMULTISIG, but I'm hoping somebody can give me some pointers into
> how to best refactor the common functionality into reusable blocks. And the
> annotating incoming transactions with their normalized inputs is a bit
> cumbersome, maye somebody has some pointers here as well?

This doesn't completely close malleability (which should be documented in the 
BIP), so I'm not sure it's worth the cost, especially if closing malleability 
later on would need more. How about specifying flags upfront in the UTXO-
creating transaction specifying which parts the signature will cover? This 
would allow implementation of fully malleability-proof wallets.

Additionally, you have a flag to control whether the opcode behaves as VERIFY 
or not. Non-VERIFY is not possible as a softfork (without doing a second/new 
P2SH) since it can be negated.

Luke