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From: "Russell O'Connor" <roconnor@blockstream.com>
Date: Sun, 4 Jul 2021 22:10:17 -0400
Message-ID: <CAMZUoKnjAd8hUpa5nZyPWTx_uxHtLL8XOjbROxobfAC+6yMWUA@mail.gmail.com>
To: ZmnSCPxj <ZmnSCPxj@protonmail.com>, 
 Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
Content-Type: multipart/alternative; boundary="0000000000002f71fd05c656cfb4"
Subject: Re: [bitcoin-dev] Unlimited covenants,
 was Re: CHECKSIGFROMSTACK/{Verify} BIP for Bitcoin
Precedence: list

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On Sun, Jul 4, 2021 at 9:02 PM Russell O'Connor <roconnor@blockstream.com>
wrote:

> Bear in mind that when people are talking about enabling covenants, we are
> talking about whether OP_CAT should be allowed or not.
>
> That said, recursive covenants, the type that are most worrying, seems to
> require some kind of OP_TWEAK operation, and I haven't yet seen any
> evidence that this can be simulated with CHECKSIG(FROMSTACK).  So maybe we
> should leave such worries for the OP_TWEAK operation.
>

Upon further thought, you can probably make recursive covenants even with a
fixed scritpubkey by sneaking the state into a few bits of the UTXO's
amount.  Or if you try really hard, you may be able to stash your state
into a sibling output that is accessed via the txid embedded in the
prevoutpoint.

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<div dir=3D"ltr"><div class=3D"gmail_quote"><div dir=3D"ltr" class=3D"gmail=
_attr">On Sun, Jul 4, 2021 at 9:02 PM Russell O&#39;Connor &lt;<a href=3D"m=
ailto:roconnor@blockstream.com">roconnor@blockstream.com</a>&gt; wrote:<br>=
</div><blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;b=
order-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir=3D"ltr"><d=
iv>Bear in mind that when people are talking about enabling covenants, we a=
re talking about whether OP_CAT should be allowed or not.</div><div><br></d=
iv><div>That said, recursive covenants, the type that are most worrying, se=
ems to require some kind of OP_TWEAK operation, and I haven&#39;t yet seen =
any evidence that this can be simulated with CHECKSIG(FROMSTACK).=C2=A0 So =
maybe we should leave such worries for the OP_TWEAK operation.<br></div></d=
iv></blockquote><div><br></div><div>Upon further thought, you can probably =
make recursive covenants even with a fixed scritpubkey by sneaking the stat=
e into a few bits of the UTXO&#39;s amount.=C2=A0 Or if you try really hard=
, you may be able to stash your state into a sibling output that is accesse=
d via the txid embedded in the prevoutpoint.<br></div></div></div>

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