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From: "Russell O'Connor" <roconnor@blockstream.io>
To: Johnson Lau <jl2012@xbt.hk>
Cc: Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] Safer sighashes and more granular SIGHASH_NOINPUT
Date: Thu, 22 Nov 2018 11:23:54 -0500	[thread overview]
Message-ID: <CAMZUoKkhrLKOaquP1_M9GwuKT1u7d+GoyW6tcK-t2uv+5VRfyA@mail.gmail.com> (raw)
In-Reply-To: <64A86A3A-4633-4BE2-AE09-30BD136BCC2D@xbt.hk>

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I see, so your suggestion is that a sequence of OP_IF ... OP_ENDIF can be
replaced by a Merklized Script tree of that depth in practice.

I'm concerned that at script creation time it takes exponential time to
complete a Merkle root of depth 'n'.  Can anyone provide benchmarks or
estimates of how long it takes to compute a Merkle root of a full tree of
various depths on typical consumer hardware?  I would guess things stop
becoming practical at a depth of 20-30.

On Thu, Nov 22, 2018 at 9:28 AM Johnson Lau <jl2012@xbt.hk> wrote:

> With MAST in taproot, OP_IF etc become mostly redundant, with worse
> privacy. To maximise fungibility, we should encourage people to use MAST,
> instead of improve the functionality of OP_IF and further complicate the
> protocol.
>
>
> On 22 Nov 2018, at 1:07 AM, Russell O'Connor via bitcoin-dev <
> bitcoin-dev@lists.linuxfoundation.org> wrote:
>
> On Mon, Nov 19, 2018 at 10:22 PM Pieter Wuille via bitcoin-dev <
> bitcoin-dev@lists.linuxfoundation.org> wrote:
>
>> So my question is whether anyone can see ways in which this introduces
>> redundant flexibility, or misses obvious use cases?
>>
>
> Hopefully my comment is on-topic for this thread:
>
> Given that we want to move away from OP_CODESEPARATOR, because each call
> to this operation effectively takes O(script-size) time, we need a
> replacement for the functionality it currently provides.  While perhaps the
> original motivation for OP_CODESEPARTOR is surrounded in mystery, it
> currently can be used (or perhaps abused) for the task of creating
> signature that covers, not only which input is being signed, but which
> specific branch within that input Script code is being signed for.
>
> For example, one can place an OP_CODESEPARATOR within each branch of an IF
> block, or by placing an OP_CODESEPARATOR before each OP_CHECKSIG
> operation.  By doing so, signatures created for one clause cannot be used
> as signatures for another clause.  Since different clauses in Bitcoin
> Script may be enforcing different conditions (such as different time-locks,
> hash-locks, etc), it is useful to be able to sign in such a way that your
> signature is only valid when the conditions for a particular branch are
> satisfied.  In complex Scripts, it may not be practical or possible to use
> different public keys for every different clause. (In practice, you will be
> able to get away with fewer OP_CODESEPARATORS than one in every IF block).
>
> One suggestion I heard (I think I heard it from Pieter) to achieve the
> above is to add an internal counter that increments on every control flow
> operator, OP_IF, OP_NOTIF, OP_ELSE, OP_ENDIF, and have the signature cover
> the value of this counter.  Equivalently we divide every Bitcoin Script
> program into blocks deliminated by these control flow operator and have the
> signature cover the index of the block that the OP_CHECKSIG occurs within.
> More specifically, we will want a SigHash flag to enables/disable the
> signature covering this counter.
>
> There are many different ways one might go about replacing the remaining
> useful behaviour of OP_CODESEPARATOR than the one I gave above. I would be
> happy with any solution.
> _______________________________________________
> bitcoin-dev mailing list
> bitcoin-dev@lists.linuxfoundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
>
>
>

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  reply	other threads:[~2018-11-22 16:24 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 [this message]
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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