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Jun 17, 2021
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zkSNARK Plonk #454

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create zkSNARK plonk
ashWhiteHat Jun 14, 2021
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8 changes: 6 additions & 2 deletions applications/zk-plonk.md
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Expand Up @@ -97,10 +97,14 @@ We plan to provide a `plonk` pallet that allows Substrate-based blockchain to ex
| 0b. | Documentation | We will provide both inline documentation of the code and a basic tutorial that explains how a developer builds a circuit and a user prove their computation through the circuit. |
| 0c. | Testing Guide | Core functions will be fully covered by unit tests and audit to ensure functionality and robustness. In the guide, we will describe how to run these tests. |
| 0d. | Article/Tutorial | We will publish an article/tutorial/workshop that explains
| 1. | make plonk compatible | The dusk-network plonk is compatible with `no-std` so we are going to modify attributes according to [parity-codec](https://github.com/paritytech/parity-scale-codec) and `Rng` to be compatible with　Substrate environment. |
| 2. | implement zkSNARK plonk pallet | We will create a set of plonk-based zkSNARK libraries that allow a developer to build their own circuit and a user to prove their computation validity. |
| 1. | make plonk compatible | The dusk-network plonk is compatible with `no-std` so we are going to modify attributes according to [parity-codec](https://github.com/paritytech/parity-scale-codec) and `Rng` to be compatible with　Substrate environment. This step allows this pallet to work on resource-constrained execution environments like Substrate runtime, attributes should be modified in accordance with SCALE codec and some versions of Rng can’t be compiled to wasm so we need to research and make it stable as necessary. |
| 2. | implement zkSNARK plonk pallet | We will create a set of plonk-based zkSNARK libraries that allow a developer to build their own circuit and a user to prove their computation validity. Verifying proofs are done by on-chain. Creating the proofs are done by off-chain. |

@mmagician mmagician Jun 16, 2021

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off chain - meaning off-chain worker? or a separate tool?

@ashWhiteHat ashWhiteHat Jun 17, 2021

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Creating the proofs is done by an off-chain worker.


This zkSNARK plonk is based on [dusk-network plonk](https://github.com/dusk-network/plonk) library.
This zkSNARK plonk pallet provides us following function.
- Building circuits

@mmagician mmagician Jun 16, 2021

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You're planning to build circuits through your pallet? This sounds like you're planning to make it interactive, which doesn't make much sense to me, since circuits needed to be programmed by the user. As far as I'm aware, this involves writing code with the help of some tools (like circom, or dusk-plonk would be the fit here I guess) that is later compiled. Please expand on how your pallet would support building circuits

@ashWhiteHat ashWhiteHat Jun 17, 2021 •
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Hi @mmagician
Thank you for asking me for details.

You're planning to build circuits through your pallet? This sounds like you're planning to make it interactive, which doesn't make much sense to me, since circuits needed to be programmed by the user.

Yes, the user(Substrate developer) can build their own programmable circuit.

If they want to build a circuit of privacy transfer, following sequence they need.

  1. Build their own circuit on-chain(Substrate node) that checks the validity of transactions
  2. Customize off-chain worker library corresponding to the on-chain circuit
  3. Deploy the Substrate node
  4. The transactor creates proofs and sends transactions through the off-chain worker.

It's a similar structure with circom which deploys verifier contract and this is the verify pallet of this project.
The circom creates proof using the off-chain library and this is the create proof off-chain worker of this project.

@mmagician mmagician Jun 17, 2021

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If you don't mind I'll lean on the example from circom again. From this tutorial section 2.1, a user needs to write code in order to build their circuit.

So what you're saying is that if a developer wants to build their own circuit, they need to have a separate pallet with the logic for their own circuit? Because, as far as I understand, each circuit will be customised for the developer's own purpose and it's difficult to make it generic.

I could imagine that if there is a common interface, an off-chain worker could be called to build the circuit from whatever code the user has written. Could it be generic enough?

Well if that's the case and I understood your last comment, then the building of the circuit will not happen in your pallet, but rather each developer has to do it independently. And then they can call your pallet's create proof method (assuming there is some standard interface in place) to take whatever circuit they built, supply the secret inputs, and compute the proof. Is my understanding correct?

@ashWhiteHat ashWhiteHat Jun 17, 2021

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Thank you for the questions.

If you don't mind I'll lean on the example from circom again. From this tutorial section 2.1, a user needs to write code in order to build their circuit.

This plonk pallet provides a circuit template library.
A user writes code on the provided circuit template library so it doesn't have to have a separate library by itself in the same way as a circom user doesn't need to implement any kind of library just defining constraint.

they need to have a separate pallet with the logic for their own circuit?

No, because this plonk pallet provides a circuit template library.

each circuit will be customised for the developer's own purpose and it's difficult to make it generic.

Each circuit will be customized using a circuit template library and a user define the constraint themselves.

I could imagine that if there is a common interface, an off-chain worker could be called to build the circuit from whatever code the user has written.

Sorry I couldn't understand this.
The circuit can't be added after a developer deploys the Substrate node.

the building of the circuit will not happen in your pallet

The building of the circuit will happen in this plonk pallet using a circuit template library.
A user defines the circuit as following through the plonk pallet.

impl Circuit for TestCircuit {
    const CIRCUIT_ID: [u8; 32] = [0xff; 32];
    fn gadget(
        &mut self,
        composer: &mut StandardComposer,
    ) -> Result<(), Error> {
        let a = composer.add_input(self.a);
        let b = composer.add_input(self.b);
        // Make first constraint a + b = c
        composer.poly_gate(
            a,
            b,
            composer.zero_var(),
            BlsScalar::zero(),
            BlsScalar::one(),
            BlsScalar::one(),
            BlsScalar::zero(),
            BlsScalar::zero(),
            Some(-self.c),
        );
        // Check that a and b are in range
        composer.range_gate(a, 1 << 6);
        composer.range_gate(b, 1 << 5);
        // Make second constraint a * b = d
        composer.poly_gate(
            a,
            b,
            composer.zero_var(),
            BlsScalar::one(),
            BlsScalar::zero(),
            BlsScalar::zero(),
            BlsScalar::one(),
            BlsScalar::zero(),
            Some(-self.d),
        );

        let e = composer.add_input(self.e.into());
        let scalar_mul_result = composer
            .fixed_base_scalar_mul(e, dusk_jubjub::GENERATOR_EXTENDED);
        // Apply the constrain
        composer.assert_equal_public_point(scalar_mul_result, self.f);
        Ok(())
    }
    fn padded_circuit_size(&self) -> usize {
        1 << 11
    }
}

A user circuit is TestCircuit and the Circuit struct is from this pallet.
A user can build a circuit by extending provided Circuit struct and this is a generic circuit template library.
And from the next line, a user defines the constraint.
I hope this example helps you to understand well.
Sorry that was such a long comment 🙇‍♂️

- Creating proofs
- Verifying proofs

## Future Plans

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