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From: "Russell O'Connor" <roconnor@blockstream.com>
To: Jeremy Rubin <jeremy.l.rubin@gmail.com>
Cc: Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] TXHASH + CHECKSIGFROMSTACKVERIFY in lieu of CTV and ANYPREVOUT
Date: Tue, 15 Feb 2022 14:12:30 -0500	[thread overview]
Message-ID: <CAMZUoK==_4Eqe690B0oiKRopRsKKZc02oupkk+Kc9++hizKJDA@mail.gmail.com> (raw)
In-Reply-To: <CAD5xwhi4y1NiZ__c1WY-rCV3XBzN5yxY1Zox6Mc1FTjxUhXK9A@mail.gmail.com>

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On Tue, Feb 15, 2022 at 1:57 PM Jeremy Rubin <jeremy.l.rubin@gmail.com>
wrote:

> Hi Rusty,
>
> Please see my post in the other email thread
> https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2022-February/019886.html
>
> The differences in this regard are several, and worth understanding beyond
> "you can iterate CTV". I'd note a few clear examples for showing that "CTV
> is just as powerful" is not a valid claim:
>
> 1) CTV requires the contract to be fully enumerated and is non-recursive.
> For example, a simple contract that allows n participants to take an action
> in any order requires factorially many pre-computations, not just linear or
> constant. For reference, 24! is about 2**80. Whereas for a more
> interpretive covenant -- which is often introduced with the features for
> recursion -- you can compute the programs for these addresses in constant
> time.
> 2) CTV requires the contract to be fully enumerated: For example, a simple
> contract one could write is "Output 0 script matches Output 1", and the set
> of outcomes is again unbounded a-priori. With CTV you need to know the set
> of pairs you'd like to be able to expand to a-priori
> 3) Combining 1 and 2, you could imagine recursing on an open-ended thing
> like creating many identical outputs over time but not constraining what
> those outputs are. E.g., Output 0 matches Input 0, Output 1 matches Output
> 2.
>
> I think for your point the inverse seems to hold: for the limited
> situations we might want to set up, CTV often ends up being sufficient
> because usually we can enumerate all the possible outcomes we'd like (or at
> least find a mapping onto such a construction). CTV is indeed very
> powerful, but as I demonstrated above, not powerful in the same way
> ("Complexity Class") that OP_TX or TXHASH might be.
>

Just to be clear, if OP_TXHASH is restricted to including the flags for the
values to be hashed (at least for OP_TXHASH0), we don't appear to enter
recursive covenant territory, as long as we remain without OP_CAT.


> At the very least we should clearly understand *what* and *why* we are
> advocating for more sophisticated designs and have a thorough understanding
> of the protocol complexity we are motivated to introduce the expanded
> functionality. Further, if one advocates for TX/TXHASH on a featureful
> basis, it's at least a technical ACK on the functionality CTV is
> introducing (as it is a subset) and perhaps a disagreement on project
> management, which I think is worth noting. There is a very wide gap between
> "X is unsafe" and "I prefer Y which X is a subset of ''.
>

I'm certainly of the opinion we should have some feature to enable the
commitment of outputs.  It seems quite useful in various protocols.

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  reply	other threads:[~2022-02-15 19:12 UTC|newest]

Thread overview: 58+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-01-26 17:20 [bitcoin-dev] TXHASH + CHECKSIGFROMSTACKVERIFY in lieu of CTV and ANYPREVOUT Russell O'Connor
2022-01-26 22:16 ` Jeremy
2022-01-27  4:20   ` James Lu
2022-01-27 19:16   ` Russell O'Connor
2022-01-28  0:18     ` James O'Beirne
2022-01-28 13:14       ` Michael Folkson
2022-01-28 14:17         ` Anthony Towns
2022-01-28 16:38           ` Jeremy
2022-01-28 14:13       ` Russell O'Connor
2022-01-28 15:14         ` James O'Beirne
2022-01-29 15:43           ` Russell O'Connor
2022-01-29 17:02             ` Jeremy Rubin
     [not found]             ` <CAD5xwhjHv2EGYb33p2MRS=VSz=ciGwAsiafX1yRHjxQEXfykSA@mail.gmail.com>
2022-01-29 17:14               ` Russell O'Connor
2022-01-31  2:18       ` Anthony Towns
2022-01-28  1:34 ` Anthony Towns
2022-01-28 13:56   ` Russell O'Connor
2022-02-01  1:16     ` Anthony Towns
2022-02-08  2:16       ` Russell O'Connor
2022-02-17 14:27         ` Anthony Towns
2022-02-17 14:50           ` Russell O'Connor
2022-02-08  3:40 ` Rusty Russell
2022-02-08  4:34   ` Jeremy Rubin
2022-02-11  0:55     ` [bitcoin-dev] Recursive covenant opposition, or the absence thereof, was " David A. Harding
2022-02-11  3:42       ` Jeremy Rubin
2022-02-11 17:42       ` James O'Beirne
2022-02-11 18:12         ` digital vagabond
2022-02-12 10:54           ` darosior
2022-02-12 15:59             ` Billy Tetrud
2022-02-17 15:15           ` Anthony Towns
2022-02-18  7:34       ` ZmnSCPxj
2022-02-23 11:28       ` ZmnSCPxj
2022-02-23 18:14         ` Paul Sztorc
2022-02-24  2:20           ` ZmnSCPxj
2022-02-24  6:53         ` Anthony Towns
2022-02-24 12:03           ` ZmnSCPxj
2022-02-26  5:38             ` Billy Tetrud
2022-02-26  6:43               ` ZmnSCPxj
2022-02-27  0:58                 ` Paul Sztorc
2022-02-27  2:00                   ` ZmnSCPxj
2022-02-27  7:25                     ` ZmnSCPxj
2022-02-27 16:59                       ` Billy Tetrud
2022-02-27 23:50                         ` Paul Sztorc
2022-02-28  0:20                     ` Paul Sztorc
2022-02-28  6:49                       ` ZmnSCPxj
2022-02-28  7:55                         ` vjudeu
2022-03-04  8:42                           ` ZmnSCPxj
2022-03-04 13:43                             ` vjudeu
2022-02-28 22:54                         ` Paul Sztorc
2022-03-01  5:39                           ` Billy Tetrud
2022-03-02  0:00                             ` Paul Sztorc
2022-03-04 12:35                               ` Billy Tetrud
2022-03-04 20:06                                 ` Paul Sztorc
2022-02-26  6:00             ` Anthony Towns
2022-02-15  8:45     ` [bitcoin-dev] " Rusty Russell
2022-02-15 18:57       ` Jeremy Rubin
2022-02-15 19:12         ` Russell O'Connor [this message]
2022-02-16  2:26         ` Rusty Russell
2022-02-16  4:10           ` Russell O'Connor

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