Subject: Re: [bitcoin-dev] New BIP: Dealing with OP_IF and OP_NOTIF malleability in P2WSH

From: Pieter Wuille <[email-masked]>
Date: Wed, 17 Aug 2016 00:30:52 +0200

On Aug 17, 2016 00:23, "Russell O'Connor via bitcoin-dev" <
[email-masked]> wrote:

> If one's goal is to mess with an transaction to prevent it from being
mined, it is more effective to just not relay the transaction rather than
to mess with the witness.  Given two transactions with the same txid and
different witness data, miners and good nodes ought to mine/relay the
version with the lower cost (smaller?) witness data.

That implies that everyone will see both versions and be able to make that
choice. Unfortunately, those two versions will be definition be in conflict
with each other, and thus only one will end up paying a fee. We're can't
relay two transactions for the price of one, or we'd expose the p2p network
to a very cheap DDoS attack: just send increasingly small versions of the
same transaction.

Segwit's third party mallebility protection makes it not an issue for
dependent contracts if transactions are mauled (=apparently the verb
related to malleability), but there are still good reasons for senders not
to gratuitously make their transactions extensible in size or other
resources.

--
Pieter