📅 Original date posted:2023-08-07
🗒️ Summary of this message: The sender thanks Salvatore for the update on taptree verification and offers suggestions on the proposal, including opcode parameter ordering and the deferred amount check.
📝 Original message:
Hi, Salvatore.
Thanks for the update! I like the fact that taptree verification now
can be done on both input and outputs, and having them be symmetrical
also makes the learning curve a bit easier.
I have implemented the updated opcodes in btcd (very rough
implementation)]1] as well as updated the example scripts for
simulating CTV[2] and Coinpools[3].
>From doing this I would again like to offer some suggestions on the proposal.
- For the opcode parameter ordering, it feels unnatural for the two
tweaks (data, taptree) to be separated by the internal key. A more
natural ordering of parameters IMO would be (of course this is all
subjective):
<data> <taptree> <internalkey> <index> <flags> OP_CCV.
If you disagree, I would love some rationale for the ordering you
chose! (looks like you also changed it again after your last post?).
- The deferred amount check seems a bit out of place, and insufficient
at least for the use cases I had in mind. They work well in a vault
setting, where you want to consolidate many outputs into a single new
one, and in 1-input-1-output settings where you want to preserve the
amount exactly. However, for coinpools, CTV with more than one output
and other interesting contracts where you want to split or combine
amounts it won't be powerful enough.
I'm wondering what other use cases you had in mind for the deferred
output amount check? Maybe I have missed something, but if not it
would perhaps be better to leave out the amount preservation check, or
go the extra mile and propose a more powerful amount introspection
machinery.
Cheers,
Johan
[1] - https://github.com/halseth/btcd/pull/1
[2] - https://github.com/halseth/tapsim/blob/8f4ac4d914fde0847c72cd22bdd45a1b7247cadf/examples/matt/ctv2/README.md
[3] - https://github.com/halseth/tapsim/blob/8f4ac4d914fde0847c72cd22bdd45a1b7247cadf/examples/matt/coinpool/README.md
On Sun, Jul 30, 2023 at 11:51 PM Salvatore Ingala via bitcoin-dev
<bitcoin-dev at lists.linuxfoundation.org> wrote:
>
> Hi all,
>
> I have put together a first complete proposal for the core opcodes of
> MATT [1][2].
> The changes make the opcode functionally complete, and the
> implementation is revised and improved.
>
> The code is implemented in the following fork of the
> bitcoin-inquisition repo:
>
> https://github.com/Merkleize/bitcoin/tree/checkcontractverify
>
> Therefore, it also includes OP_CHECKTEMPLATEVERIFY, as in a
> previous early demo for vaults [3].
>
> Please check out the diff [4] if you are interested in the
> implementation details. It includes some basic functional tests for
> the main cases of the opcode.
>
> ## Changes vs the previous draft
>
> These are the changes compared to the initial incomplete proposal:
> - OP_CHECK{IN,OUT}CONTRACTVERIFY are replaced by a single opcode
> OP_CHECKCONTRACTVERIFY (CCV). An additional `flags` parameter allows
> to specify if the opcode operates on an input or an output.
> This also allows inspection of other inputs, that was not possible
> with the original opcodes.
> - For outputs, the default behavior is to have the following deferred
> checks mechanism for amounts: all the inputs that have a CCV towards
> the same output, have their input amounts summed, and that act as a
> lower bound for that output's amount.
> A flag can disable this behavior. [*]
> - A number of special values of the parameters were defined in order
> to optimize for common cases, and add some implicit introspection.
> - The order of parameters is modified (particularly, <data> is at the
> bottom of the arguments, as so is more natural when writing Scripts).
>
> ## Semantics
>
> The new OP_CHECKCONTRACTVERIFY takes 5 parameters from the stack:
>
> <data>, <index>, <pk>, <taptree>, <flags>
>
> The core logic of the opcode is as follows:
>
> "Check if the <index>-th input/output's scriptPubKey is a P2TR
> whose public key is obtained from <pk>, (optionally) tweaked with
> <data>, (optionally) tap-tweaked with <taptree>".
>
> The following are special values of the parameters:
>
> - if <pk> is empty, it is replaced with a fixed NUMS point. [**]
> - if <pk> is -1, it is replaced with the current input's taproot
> internal key.
> - if <index> is -1, it is replaced with the current input's index.
> - if <data> is empty, the data tweak is skipped.
> - if <taptree> is empty, the taptweak is skipped.
> - if <taptree> is -1, it is replaced with the current input's root
> of the taproot merkle tree.
>
> There are two defined flags:
> - CCV_FLAG_CHECK_INPUT = 1: if present, <index> refers to an input;
> otherwise, it refers to an output.
> - CCV_FLAG_IGNORE_OUTPUT_AMOUNT = 2: only defined when _CHECK_INPUT
> is absent, it disables the deferred checks logic for amounts.
>
> Finally, if both the flags CCV_FLAG_CHECK_INPUT and
> CCV_FLAG_IGNORE_OUTPUT_AMOUNT are absent:
> - Add the current input's amount to the <index>-th output's bucket.
>
> After the evaluation of all inputs, it is verified that each output's
> amount is greater than or equal to the total amount in the bucket
> if that output (validation of the deferred checks).
>
> ## Comment
>
> It is unclear if all the special values above will be useful in
> applications; however, as each special case requires very little added
> code, I tried to make the specs as flexible as possible at this time.
>
> With this new opcode, the full generality of MATT (including the fraud
> proofs) can be obtained with just two opcodes: OP_CHECKCONTRACTVERIFY
> and OP_CAT.
> However, additional opcodes (and additional introspection) would
> surely benefit some applications.
>
> I look forward to your comments, and to start drafting a BIP proposal.
>
> Best,
> Salvatore Ingala
>
>
> [*] - Credits go to James O'Beirne for this approach, taken from his
> OP_VAULT proposal. I cherry-picked the commit containing the
> Deferred Checks framework.
> [**] - The same NUMS point suggested in BIP-0341 was used.
>
>
> References:
>
> [1] - https://merkle.fun/
> [2] - https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2022-November/021182.html
> [3] - https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2023-April/021588.html
> [4] - https://github.com/bitcoin-inquisition/bitcoin/compare/24.0...Merkleize:bitcoin:checkcontractverify
> _______________________________________________
> bitcoin-dev mailing list
> bitcoin-dev at lists.linuxfoundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
Johan Torås Halseth [ARCHIVE] /
npub1pp…hs2fw
2023-08-08 14:20:52
in reply to nevent1q…t60e
Author Public Key
npub1ppn2nhlfdzkw9gw0ytljpef5dpyzsxzw8ffcyykamt32hw6pge0smhs2fwPublished at
2023-08-08 14:20:52Event JSON
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"created_at": 1691504452,
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"content": "📅 Original date posted:2023-08-07\n🗒️ Summary of this message: The sender thanks Salvatore for the update on taptree verification and offers suggestions on the proposal, including opcode parameter ordering and the deferred amount check.\n📝 Original message:\nHi, Salvatore.\n\nThanks for the update! I like the fact that taptree verification now\ncan be done on both input and outputs, and having them be symmetrical\nalso makes the learning curve a bit easier.\n\nI have implemented the updated opcodes in btcd (very rough\nimplementation)]1] as well as updated the example scripts for\nsimulating CTV[2] and Coinpools[3].\n\n\u003eFrom doing this I would again like to offer some suggestions on the proposal.\n\n- For the opcode parameter ordering, it feels unnatural for the two\ntweaks (data, taptree) to be separated by the internal key. A more\nnatural ordering of parameters IMO would be (of course this is all\nsubjective):\n\u003cdata\u003e \u003ctaptree\u003e \u003cinternalkey\u003e \u003cindex\u003e \u003cflags\u003e OP_CCV.\n\nIf you disagree, I would love some rationale for the ordering you\nchose! (looks like you also changed it again after your last post?).\n\n- The deferred amount check seems a bit out of place, and insufficient\nat least for the use cases I had in mind. They work well in a vault\nsetting, where you want to consolidate many outputs into a single new\none, and in 1-input-1-output settings where you want to preserve the\namount exactly. However, for coinpools, CTV with more than one output\nand other interesting contracts where you want to split or combine\namounts it won't be powerful enough.\n\nI'm wondering what other use cases you had in mind for the deferred\noutput amount check? Maybe I have missed something, but if not it\nwould perhaps be better to leave out the amount preservation check, or\ngo the extra mile and propose a more powerful amount introspection\nmachinery.\n\nCheers,\nJohan\n\n[1] - https://github.com/halseth/btcd/pull/1\n[2] - https://github.com/halseth/tapsim/blob/8f4ac4d914fde0847c72cd22bdd45a1b7247cadf/examples/matt/ctv2/README.md\n[3] - https://github.com/halseth/tapsim/blob/8f4ac4d914fde0847c72cd22bdd45a1b7247cadf/examples/matt/coinpool/README.md\n\n\nOn Sun, Jul 30, 2023 at 11:51 PM Salvatore Ingala via bitcoin-dev\n\u003cbitcoin-dev at lists.linuxfoundation.org\u003e wrote:\n\u003e\n\u003e Hi all,\n\u003e\n\u003e I have put together a first complete proposal for the core opcodes of\n\u003e MATT [1][2].\n\u003e The changes make the opcode functionally complete, and the\n\u003e implementation is revised and improved.\n\u003e\n\u003e The code is implemented in the following fork of the\n\u003e bitcoin-inquisition repo:\n\u003e\n\u003e https://github.com/Merkleize/bitcoin/tree/checkcontractverify\n\u003e\n\u003e Therefore, it also includes OP_CHECKTEMPLATEVERIFY, as in a\n\u003e previous early demo for vaults [3].\n\u003e\n\u003e Please check out the diff [4] if you are interested in the\n\u003e implementation details. It includes some basic functional tests for\n\u003e the main cases of the opcode.\n\u003e\n\u003e ## Changes vs the previous draft\n\u003e\n\u003e These are the changes compared to the initial incomplete proposal:\n\u003e - OP_CHECK{IN,OUT}CONTRACTVERIFY are replaced by a single opcode\n\u003e OP_CHECKCONTRACTVERIFY (CCV). An additional `flags` parameter allows\n\u003e to specify if the opcode operates on an input or an output.\n\u003e This also allows inspection of other inputs, that was not possible\n\u003e with the original opcodes.\n\u003e - For outputs, the default behavior is to have the following deferred\n\u003e checks mechanism for amounts: all the inputs that have a CCV towards\n\u003e the same output, have their input amounts summed, and that act as a\n\u003e lower bound for that output's amount.\n\u003e A flag can disable this behavior. [*]\n\u003e - A number of special values of the parameters were defined in order\n\u003e to optimize for common cases, and add some implicit introspection.\n\u003e - The order of parameters is modified (particularly, \u003cdata\u003e is at the\n\u003e bottom of the arguments, as so is more natural when writing Scripts).\n\u003e\n\u003e ## Semantics\n\u003e\n\u003e The new OP_CHECKCONTRACTVERIFY takes 5 parameters from the stack:\n\u003e\n\u003e \u003cdata\u003e, \u003cindex\u003e, \u003cpk\u003e, \u003ctaptree\u003e, \u003cflags\u003e\n\u003e\n\u003e The core logic of the opcode is as follows:\n\u003e\n\u003e \"Check if the \u003cindex\u003e-th input/output's scriptPubKey is a P2TR\n\u003e whose public key is obtained from \u003cpk\u003e, (optionally) tweaked with\n\u003e \u003cdata\u003e, (optionally) tap-tweaked with \u003ctaptree\u003e\".\n\u003e\n\u003e The following are special values of the parameters:\n\u003e\n\u003e - if \u003cpk\u003e is empty, it is replaced with a fixed NUMS point. [**]\n\u003e - if \u003cpk\u003e is -1, it is replaced with the current input's taproot\n\u003e internal key.\n\u003e - if \u003cindex\u003e is -1, it is replaced with the current input's index.\n\u003e - if \u003cdata\u003e is empty, the data tweak is skipped.\n\u003e - if \u003ctaptree\u003e is empty, the taptweak is skipped.\n\u003e - if \u003ctaptree\u003e is -1, it is replaced with the current input's root\n\u003e of the taproot merkle tree.\n\u003e\n\u003e There are two defined flags:\n\u003e - CCV_FLAG_CHECK_INPUT = 1: if present, \u003cindex\u003e refers to an input;\n\u003e otherwise, it refers to an output.\n\u003e - CCV_FLAG_IGNORE_OUTPUT_AMOUNT = 2: only defined when _CHECK_INPUT\n\u003e is absent, it disables the deferred checks logic for amounts.\n\u003e\n\u003e Finally, if both the flags CCV_FLAG_CHECK_INPUT and\n\u003e CCV_FLAG_IGNORE_OUTPUT_AMOUNT are absent:\n\u003e - Add the current input's amount to the \u003cindex\u003e-th output's bucket.\n\u003e\n\u003e After the evaluation of all inputs, it is verified that each output's\n\u003e amount is greater than or equal to the total amount in the bucket\n\u003e if that output (validation of the deferred checks).\n\u003e\n\u003e ## Comment\n\u003e\n\u003e It is unclear if all the special values above will be useful in\n\u003e applications; however, as each special case requires very little added\n\u003e code, I tried to make the specs as flexible as possible at this time.\n\u003e\n\u003e With this new opcode, the full generality of MATT (including the fraud\n\u003e proofs) can be obtained with just two opcodes: OP_CHECKCONTRACTVERIFY\n\u003e and OP_CAT.\n\u003e However, additional opcodes (and additional introspection) would\n\u003e surely benefit some applications.\n\u003e\n\u003e I look forward to your comments, and to start drafting a BIP proposal.\n\u003e\n\u003e Best,\n\u003e Salvatore Ingala\n\u003e\n\u003e\n\u003e [*] - Credits go to James O'Beirne for this approach, taken from his\n\u003e OP_VAULT proposal. I cherry-picked the commit containing the\n\u003e Deferred Checks framework.\n\u003e [**] - The same NUMS point suggested in BIP-0341 was used.\n\u003e\n\u003e\n\u003e References:\n\u003e\n\u003e [1] - https://merkle.fun/\n\u003e [2] - https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2022-November/021182.html\n\u003e [3] - https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2023-April/021588.html\n\u003e [4] - https://github.com/bitcoin-inquisition/bitcoin/compare/24.0...Merkleize:bitcoin:checkcontractverify\n\u003e _______________________________________________\n\u003e bitcoin-dev mailing list\n\u003e bitcoin-dev at lists.linuxfoundation.org\n\u003e https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev",
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