> Looks like `OP_CAT` is not getting enabled until after we are reasonably sure
> that recursive covenants are not really unsafe.
Maybe we should use OP_SUBSTR instead of OP_CAT. Or even better: OP_SPLIT.
Then, we could have OP_SPLIT <n> <pos1> <pos2> ... <posN> that would split a
string N times (so there will be N+1 pieces). Or we could have just OP_SPLIT
<pos> to split one string into two. Or maybe OP_2SPLIT and OP_3SPLIT, just to
split into two or three pieces (as we have OP_2DUP and OP_3DUP). I think
OP_SUBSTR or OP_SPLIT is better than OP_CAT, because then things always get
smaller and we can be always sure that we will have one byte as the smallest
unit in our Script.
On 2022-05-08 04:20:19 user ZmnSCPxj via bitcoin-dev
<bitcoin-dev@lists.linuxfoundation.org> wrote:
> Good morning shesek,
> On Sat, May 7, 2022 at 5:08 PM ZmnSCPxj via bitcoin-dev
> <bitcoin-dev@lists.linuxfoundation.org> wrote:
> > * Even ***with*** `OP_CAT`, the following will enable non-recursive
> > covenants without enabling recursive covenants:
> > * `OP_CTV`, ...
> > * With `OP_CAT`, the following would enable recursive covenants:
> > * `OP_CHECKSIGFROMSTACK`, ...
>
> Why does CTV+CAT not enable recursive covenants while CSFS+CAT does?
>
> CTV+CAT lets you similarly assert against the outputs and verify that they
> match some dynamically constructed script.
>
> Is it because CTV does not let you have a verified copy of the input's
> prevout scriptPubKey on the stack [0], while with OP_CSFS you can because the
> signature hash covers it?
>
> But you don't actually need this for recursion. Instead of having the user
> supply the script in the witness stack and verifying it against the input to
> obtain the quine, the script can simply contain a copy of itself as an
> initial push (minus this push). You can then reconstruct the full script
> quine using OP_CAT, as a PUSH(<script>) followed by the literal <script>.
<OP_PUSH_length-of-script> OP_SWAP OP_DUP OP_CAT OP_CAT <rest of script...>
Ha, yes, looks like you are correct here.
`OP_CAT` makes *all* covenant opcodes recursive, because you can always quine
using `OP_CAT`.
By itself it does not make recursive covenants, but with probably any opcode it
would.
Looks like `OP_CAT` is not getting enabled until after we are reasonably sure
that recursive covenants are not really unsafe.
Regards,
ZmnSCPxj
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