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From: Johnson Lau <jl2012@xbt.hk>
To: ZmnSCPxj <ZmnSCPxj@protonmail.com>
Cc: bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] Safer sighashes and more granular SIGHASH_NOINPUT
Date: Tue, 25 Dec 2018 05:23:44 +0800	[thread overview]
Message-ID: <4CE7B999-F1C3-4E7F-BCED-E02C5D0BE4BB@xbt.hk> (raw)
In-Reply-To: <_gOQU8sPtEG5jisR7GskWPyvzLK1xixz8-v1YbRWlAXFq9YGPyMEj9Q-xZ6CYfwgiGeJR2Qlboq4UFU_y6pur1HBG_yRTIgngWqiENmJ1Bc=@protonmail.com>

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I find another proposed use of CODESEPARATOR here: https://lists.linuxfoundation.org/pipermail/lightning-dev/2016-March/000455.html <https://lists.linuxfoundation.org/pipermail/lightning-dev/2016-March/000455.html>

<KeyA> OP_CHECKSIG
OP_IF
<KeyB>
OP_ELSE
<Delay> OP_CSV OP_DROP
OP_CODESEPARATOR <KeyA>
OP_ENDIF
OP_CHECKSIG
It is actually 2 scripts:

S1: <KeyA> OP_CHECKSIGVERIFY <KeyB> OP_CHECKSIG
S2: <Delay> OP_CSV OP_DROP <KeyA> OP_CHECKSIG

Under taproot, we could make Q = P + H(P||S2)G, where P = MuSig(KeyA, KeyB)

S1 becomes a direct spending with Q, and there is no need to use OP_IF or CODESEPARATOR in S2 at all.


==================

If it is only to force R reuse, there is no need to use CODESEPARATOR:

Input: <R> <S2>  <S1>  Script: 2DUP EQUAL NOT VERIFY 2 PICK SWAP CAT <key> DUP TOALTSTACK CHECKSIGVERIFY CAT FROMALTSTACK CHECKSIG

But using CODESEPARATOR will save 3 bytes
Input: <S2> <R> <S1>    Script:  OVER SWAP CAT <key> DUP TOALTSTACK CHECKSIGVERIFY CODESEPARATOR SWAP CAT FROMALTSTACK CHECKSIG

However, a much better way would be:

Input: <S> Script: <known R> SWAP CAT <key> CHECKSIG

The discrete log of R could be a shared secret between A and B. If the purpose is to publish the private key to the whole world, R = G could be used.

> On 24 Dec 2018, at 8:01 PM, ZmnSCPxj <ZmnSCPxj@protonmail.com> wrote:
> 
> Good morning,
> 
>> Could anyone propose a better use case of CODESEPARATOR?
> 
> Long ago, aj sent an email on Lightning-dev about use of CODESEPARATOR to impose Scriptless Script even without Schnorr. It involved 3 signatures with different CODESEPARATOR places, and forced R reuse so that the signatures to claim the funds revealed the privkey.
> 
> The script shown had all CODESEPARATOR in a single branch.
> 
> I cannot claim to understand the script, and am having difficulty digging through the mailinglist
> 
> Regards,
> ZmnSCPxj


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  reply	other threads:[~2018-12-24 21:24 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
2018-12-24 12:01                         ` ZmnSCPxj
2018-12-24 21:23                           ` Johnson Lau [this message]
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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