From: Anthony Towns <aj@erisian•com.au>
To: Christian Decker <decker.christian@gmail•com>,
Bitcoin Protocol Discussion
<bitcoin-dev@lists•linuxfoundation.org>
Subject: Re: [bitcoin-dev] Safer sighashes and more granular SIGHASH_NOINPUT
Date: Fri, 23 Nov 2018 16:04:04 +1000 [thread overview]
Message-ID: <20181123060404.fu4eyzcynbppmjcy@erisian.com.au> (raw)
In-Reply-To: <87k1l6d6lb.fsf@gmail.com>
On Wed, Nov 21, 2018 at 12:15:44PM +0100, Christian Decker via bitcoin-dev wrote:
> One minor thing that I noticed a while ago and that I meant
> to fix on BIP118 is that `hashSequence` does not need to be blanked for
> eltoo to work (since where it is needed we also use `sighash_single`),
> so I'm tempted to remove that redundant blanking. It may not make a lot
> of difference but it'd limit the ability to change the number of inputs
> to a NOINPUT transaction (this now being the only field that commits to
> the set of inputs).
Commiting to just the sequence numbers seems really weird to me; it
only really prevents you from adding inputs, since you could still
replace any input that was meant to be there by almost any arbitrary
other transaction...
I could see this *maybe* making sense if you at least committed to the
values of each input's outpoint; since that would be an actual constraint?
I don't think you can commit to anything else about the other inputs:
-- txids of the other transactions wouldn't work if you had other
NOINPUT txes, and would introduce O(N^2) validation cost if someone
signed every input with NOINPUT but committed to the txids of
every other input
-- scriptPubKeys wouldn't really work for eltoo-like constructions
that want to vary the scripts but apply the same sig, but might
work sometimes?
-- witness scripts for the other inputs could be unknown at your
signing time, or arbitrarily large and thus a pain to have to send
to a hardware wallet
Just treating NOINPUT as a subset of ANYONECANPAY seems simpler to
me though...
> As for your proposal, I really like the `sighash_scriptmask` proposal,
> and committing to the fees (with the `nofee` escape hatch) also works
> seems also a nice fix. My one concern is that introducing a new opcode
> to mask things in the sighash looks like a similar layering violation as
> `codeseparator` was, but that's just a minor issue imho.
I think OP_MASK is okay as far as layering goes, if you just think of it
as a (set of) multibyte "OP_MASKED_PUSH" opcode(s). So when you
pseudocode a script like:
<n> OP_CSV OP_DROP <p> OP_CHECKSIG
and then decide <n> needs to be masked, you rewrite it as:
[n] OP_CSV OP_DROP <p> OP_CHECKSIG
indicating n is masked, and don't worry about the exact bytes that will
encode the push, anymore than you currently worry about whether it's
OP_0, OP_1..16, <1..75>+1..75-bytes, PUSHDATA[1,2,3]+n+n-bytes.
As long as OP_MASK only applies to a PUSH and it's an error for OP_MASK
not to be immediately followed by that PUSH, I think that all works
out fine.
Cheers,
aj
next prev parent reply other threads:[~2018-11-23 6:04 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-19 22:37 Pieter Wuille
2018-11-20 20:29 ` Anthony Towns
2018-11-21 11:20 ` Christian Decker
2018-11-21 17:55 ` Johnson Lau
2018-11-21 11:15 ` Christian Decker
2018-11-23 6:04 ` Anthony Towns [this message]
2018-11-23 9:40 ` Christian Decker
2018-11-24 8:13 ` Johnson Lau
2018-11-21 17:07 ` Russell O'Connor
2018-11-22 14:28 ` Johnson Lau
2018-11-22 16:23 ` Russell O'Connor
2018-11-22 20:52 ` Johnson Lau
2018-11-22 22:10 ` Russell O'Connor
2018-11-23 10:47 ` Johnson Lau
2018-11-23 5:03 ` Anthony Towns
2018-11-23 20:18 ` Russell O'Connor
2018-11-28 3:41 ` Pieter Wuille
2018-11-28 8:31 ` Johnson Lau
2018-11-29 17:00 ` Christian Decker
2018-11-29 18:29 ` Christian Decker
2018-12-06 16:57 ` Russell O'Connor
2018-12-09 19:13 ` Johnson Lau
2018-12-11 22:50 ` Russell O'Connor
2018-12-12 19:53 ` Johnson Lau
2018-12-13 16:50 ` Russell O'Connor
2018-12-13 0:05 ` Anthony Towns
2018-12-13 16:21 ` Russell O'Connor
2018-12-14 0:47 ` Anthony Towns
[not found] ` <CAAS2fgRma+Pw-rHJSOKRVBqoxqJ3AxHO9d696fWoa-sb17JEOQ@mail.gmail.com>
2018-12-13 16:34 ` Russell O'Connor
2018-12-09 22:41 ` David A. Harding
2018-12-11 15:36 ` Russell O'Connor
2018-12-11 17:47 ` David A. Harding
2018-12-12 9:42 ` Rusty Russell
2018-12-12 20:00 ` Johnson Lau
2018-12-12 23:49 ` Rusty Russell
2018-12-13 0:37 ` Rusty Russell
2018-12-14 9:30 ` Anthony Towns
2018-12-14 13:55 ` Johnson Lau
2018-12-17 3:10 ` Rusty Russell
2018-12-20 19:34 ` Johnson Lau
2018-12-20 23:17 ` Rusty Russell
2018-12-21 18:54 ` Johnson Lau
2018-12-23 4:26 ` Anthony Towns
2018-12-23 16:33 ` Johnson Lau
2018-12-24 12:01 ` ZmnSCPxj
2018-12-24 21:23 ` Johnson Lau
2018-12-16 6:55 ` Rusty Russell
2018-12-17 19:08 ` Johnson Lau
2018-12-18 4:22 ` Peter Todd
2018-12-19 0:39 ` Rusty Russell
2019-02-09 0:39 ` Pieter Wuille
2018-12-13 0:24 ` Anthony Towns
2018-11-28 0:54 Bob McElrath
2018-11-28 8:40 ` Johnson Lau
2018-11-28 14:04 ` Bob McElrath
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