public inbox for bitcoindev@googlegroups.com
 help / color / mirror / Atom feed
From: Johnson Lau <jl2012@xbt.hk>
To: Anthony Towns <aj@erisian.com.au>
Cc: bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] Safer sighashes and more granular SIGHASH_NOINPUT
Date: Mon, 24 Dec 2018 00:33:48 +0800	[thread overview]
Message-ID: <F445FD1D-52E2-41E4-8FBD-3419A6317CF6@xbt.hk> (raw)
In-Reply-To: <20181223042659.munrqfe4l6nff2ug@erisian.com.au>



> On 23 Dec 2018, at 12:26 PM, Anthony Towns <aj@erisian.com.au> wrote:
> 
> On Sat, Dec 22, 2018 at 02:54:42AM +0800, Johnson Lau wrote:
>> The question I would like to ask is: is OP_CODESEPARATOR useful under taproot? Generally speaking, CODESEPARATOR is useful only with conditional opcodes (OP_IF etc), and conditional opcodes are mostly replaced by merklized scripts. I am not sure how much usability is left with CODESEPARATOR
> 
> If you don't have conditionals, then I think committing to the (masked)
> script gives you everything you could do with codeseparator.

I don’t think CODESEPARATOR is useful without conditionals. By useful I mean making a script more compact

> 
> If you don't commit to the (masked) script, don't have conditionals,
> and don't have codeseparator, then I don't think you can make a signature
> distinguish which alternative script it's intending to sign; but you can
> just give each alternative script in the MAST a slight variation of the
> key and that seems good enough.

You can and should always use a different in different branch. If this best practice is always followed, committing to masked script is not necessary

> 
> OTOH, I think for (roughly) the example you gave:
> 
>  DEPTH 3 EQUAL
>  IF <Bob> CHECKSIGVERIFY HASH160 <H> EQUALVERIFY CODESEP
>  ELSE <n> CLTV DROP
>  ENDIF
>  <Alice> CHECKSIG
> 
> then compared to the taproot equivalent:
> 
>  P = muSig(Alice,Bob)
>  S1 = <Alice1> CHECKSIGVERIFY <Bob> CHECKSIGVERIFY HASH160 <H> EQUAL
>  S2 = <Alice2> CHECKSIGVERIFY <n> CLTV
> 
> the IF+CODESEP approach is actually cheaper (lighter weight) if you're
> mostly (>2/3rds of the time) taking the S1 branch. This is because the
> "DEPTH 3 EQUAL IF/ELSE/ENDIF CODESEP <n> CLTV DROP" overhead is less
> than the 32B overhead to choose a merkle branch).
> 
> (That said, I'm not sure what Alice's signature in the S1 branch actually
> achieves in that script; and without that in S1, the taproot approach is
> cheaper all the time. Scriptless scripts would be cheaper still)
> 
>> If no one needs CODESEPARATOR, we might just disable it, and makes the validation code a bit simpler
> 
> Since it only affects the behaviour of the checkdls (checksig) operators,
> even if it was disabled, it could be re-enabled fairly easily in a new
> script subversion if needed (ie, it could be re-added when upgrading
> witness version 1 from script version 0 to 1).
> 
> Cheers,
> aj
> 

Yes, I don’t think it needs Alice signature in S1 at all. So the original example doesn’t even need CODESEPARATOR at all. 

Could anyone propose a better use case of CODESEPARATOR?




  reply	other threads:[~2018-12-23 16:34 UTC|newest]

Thread overview: 55+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-19 22:37 [bitcoin-dev] Safer sighashes and more granular SIGHASH_NOINPUT 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
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 [this message]
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=F445FD1D-52E2-41E4-8FBD-3419A6317CF6@xbt.hk \
    --to=jl2012@xbt.hk \
    --cc=aj@erisian.com.au \
    --cc=bitcoin-dev@lists.linuxfoundation.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox