From: Anthony Towns <aj@erisian•com.au>
To: Johnson Lau <jl2012@xbt•hk>
Cc: bitcoin-dev <bitcoin-dev@lists•linuxfoundation.org>
Subject: Re: [bitcoin-dev] Safer sighashes and more granular SIGHASH_NOINPUT
Date: Sun, 23 Dec 2018 14:26:59 +1000 [thread overview]
Message-ID: <20181223042659.munrqfe4l6nff2ug@erisian.com.au> (raw)
In-Reply-To: <73F32BC6-751E-4F35-BE6D-B31170FC0A54@xbt.hk>
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.
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.
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
next prev parent reply other threads:[~2018-12-23 4:27 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
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 [this message]
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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