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From: Peter Todd <pete@petertodd.org>
To: Luke Dashjr <luke@dashjr.org>,
	Bitcoin Protocol Discussion
	<bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] New BIP: Dealing with OP_IF and OP_NOTIF malleability in P2WSH
Date: Tue, 16 Aug 2016 12:43:32 -0700	[thread overview]
Message-ID: <20160816194332.GA5888@fedora-21-dvm> (raw)
In-Reply-To: <201608161937.20748.luke@dashjr.org>

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On Tue, Aug 16, 2016 at 07:37:19PM +0000, Luke Dashjr via bitcoin-dev wrote:
> On Tuesday, August 16, 2016 5:53:08 PM Johnson Lau via bitcoin-dev wrote:
> > A new BIP is prepared to deal with OP_IF and OP_NOTIF malleability in
> > P2WSH:
> > https://github.com/jl2012/bips/blob/minimalif/bip-minimalif.mediawiki
> > https://github.com/bitcoin/bitcoin/pull/8526
> 
> I am not sure this makes sense. SegWit transactions are already non-malleable 
> due to skipping the witness data in calculating the transaction id. What is 
> the benefit to this?

SegWit txids aren't malleable, but segwit transactions as a whole still are.
For instance, I could mess with a segwit transaction by replacing part of the
witness that is used as an argument to an OP_IF with a much larger push,
potentially making the transaction larger, thus making it not get mined due to
the higher fee. There are also potential legal issues if someone replaces a
push with data where posession in your jurisdiction is illegal.

Having said that, a better approach may be a separate CHECKBOOLVERIFY opcode
that fails unless the top item on the stack is a minimally encoded true or
false value, to allow script writers to opt into this behavior; it's not always
ideal.

-- 
https://petertodd.org 'peter'[:-1]@petertodd.org

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  reply	other threads:[~2016-08-16 19:43 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-08-16 17:53 [bitcoin-dev] New BIP: Dealing with OP_IF and OP_NOTIF malleability in P2WSH Johnson Lau
2016-08-16 19:37 ` Luke Dashjr
2016-08-16 19:43   ` Peter Todd [this message]
2016-08-16 21:58     ` Joseph Poon
2016-08-16 22:23     ` Russell O'Connor
2016-08-16 22:30       ` Pieter Wuille
2016-08-16 22:36         ` Russell O'Connor
2016-08-16 22:39           ` Pieter Wuille
2016-08-16 22:52             ` Russell O'Connor
2016-08-17  0:18               ` Gregory Maxwell
2016-08-17  0:27                 ` Russell O'Connor
2016-08-17  2:30                   ` Peter Todd
2016-08-17  3:02                   ` Johnson Lau
2016-08-17  4:40                     ` Luke Dashjr
2016-08-17 10:15                       ` Johnson Lau
2016-08-18  0:11                         ` Sergio Demian Lerner
     [not found]                           ` <CAAS2fgQ=Z+xmg0DcANV4vhp+XhpL1Vz0HNkJwNGdHTxtK1q1kg@mail.gmail.com>
2016-08-18  0:33                             ` Sergio Demian Lerner
2016-08-18  3:00                               ` Peter Todd
2016-09-05 14:55             ` Russell O'Connor
2016-09-01 11:39 ` Johnson Lau
2016-09-05  1:32   ` Rusty Russell

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