darkfi/src/circuit/spend_contract.rs

use halo2::{
    circuit::{Layouter, SimpleFloorPlanner},
    plonk::{Advice, Circuit, Column, ConstraintSystem, Error, Instance as InstanceColumn},
};
use halo2_gadgets::{
    ecc::{
        chip::{EccChip, EccConfig},
        FixedPoint,
    },
    poseidon::{Hash as PoseidonHash, Pow5T3Chip as PoseidonChip, Pow5T3Config as PoseidonConfig},
    primitives::poseidon::{ConstantLength, P128Pow5T3},
    sinsemilla::{
        chip::{SinsemillaChip, SinsemillaConfig},
        merkle::{
            chip::{MerkleChip, MerkleConfig},
            MerklePath,
        },
    },
    utilities::{
        lookup_range_check::LookupRangeCheckConfig, CellValue, UtilitiesInstructions, Var,
    },
};
use pasta_curves::pallas;

use crate::crypto::constants::{
    sinsemilla::{OrchardCommitDomains, OrchardHashDomains},
    OrchardFixedBases,
};

#[allow(dead_code)]
#[derive(Clone, Debug)]
pub struct SpendConfig {
    primary: Column<InstanceColumn>,
    advices: [Column<Advice>; 10],
    ecc_config: EccConfig,
    merkle_config_1: MerkleConfig<OrchardHashDomains, OrchardCommitDomains, OrchardFixedBases>,
    merkle_config_2: MerkleConfig<OrchardHashDomains, OrchardCommitDomains, OrchardFixedBases>,
    sinsemilla_config_1:
        SinsemillaConfig<OrchardHashDomains, OrchardCommitDomains, OrchardFixedBases>,
    sinsemilla_config_2:
        SinsemillaConfig<OrchardHashDomains, OrchardCommitDomains, OrchardFixedBases>,
    poseidon_config: PoseidonConfig<pallas::Base>,
}

impl SpendConfig {
    fn ecc_chip(&self) -> EccChip<OrchardFixedBases> {
        EccChip::construct(self.ecc_config.clone())
    }

    /*
    fn sinsemilla_chip_1(
        &self,
    ) -> SinsemillaChip<OrchardHashDomains, OrchardCommitDomains, OrchardFixedBases> {
        SinsemillaChip::construct(self.sinsemilla_config_1.clone())
    }

    fn sinsemilla_chip_2(
        &self,
    ) -> SinsemillaChip<OrchardHashDomains, OrchardCommitDomains, OrchardFixedBases> {
        SinsemillaChip::construct(self.sinsemilla_config_2.clone())
    }
    */

    fn merkle_chip_1(
        &self,
    ) -> MerkleChip<OrchardHashDomains, OrchardCommitDomains, OrchardFixedBases> {
        MerkleChip::construct(self.merkle_config_1.clone())
    }

    fn merkle_chip_2(
        &self,
    ) -> MerkleChip<OrchardHashDomains, OrchardCommitDomains, OrchardFixedBases> {
        MerkleChip::construct(self.merkle_config_2.clone())
    }

    fn poseidon_chip(&self) -> PoseidonChip<pallas::Base> {
        PoseidonChip::construct(self.poseidon_config.clone())
    }
}

// The public input array offsets
const BURN_NULLIFIER_OFFSET: usize = 0;
const BURN_VALCOMX_OFFSET: usize = 1;
const BURN_VALCOMY_OFFSET: usize = 2;
const BURN_TOKCOMX_OFFSET: usize = 3;
const BURN_TOKCOMY_OFFSET: usize = 4;
const BURN_MERKLEROOT_OFFSET: usize = 5;
const BURN_SIGKEYX_OFFSET: usize = 6;
const BURN_SIGKEYY_OFFSET: usize = 7;

#[derive(Default, Debug)]
pub struct SpendContract {
    pub secret_key: Option<pallas::Base>,
    pub serial: Option<pallas::Base>,
    pub value: Option<pallas::Base>,
    pub token: Option<pallas::Base>,
    pub coin_blind: Option<pallas::Base>,
    pub value_blind: Option<pallas::Scalar>,
    pub token_blind: Option<pallas::Scalar>,
    pub leaf_pos: Option<u32>,
    pub merkle_path: Option<[pallas::Base; 32]>,
    //pub sig_secret: Option<pallas::Scalar>,
    pub sig_secret: Option<pallas::Base>,
}

impl UtilitiesInstructions<pallas::Base> for SpendContract {
    type Var = CellValue<pallas::Base>;
}

impl Circuit<pallas::Base> for SpendContract {
    type Config = SpendConfig;
    type FloorPlanner = SimpleFloorPlanner;

    fn without_witnesses(&self) -> Self {
        Self::default()
    }

    fn configure(meta: &mut ConstraintSystem<pallas::Base>) -> Self::Config {
        // Advice columns used in the circuit
        let advices = [
            meta.advice_column(),
            meta.advice_column(),
            meta.advice_column(),
            meta.advice_column(),
            meta.advice_column(),
            meta.advice_column(),
            meta.advice_column(),
            meta.advice_column(),
            meta.advice_column(),
            meta.advice_column(),
        ];

        // Fixed columns for the Sinsemilla generator lookup table
        let table_idx = meta.lookup_table_column();
        let lookup = (table_idx, meta.lookup_table_column(), meta.lookup_table_column());

        // Instance column used for public inputs
        let primary = meta.instance_column();
        meta.enable_equality(primary.into());

        // Permutation over all advice columns
        for advice in advices.iter() {
            meta.enable_equality((*advice).into());
        }

        // Poseidon requires four advice columns, while ECC incomplete addition
        // requires six. We can reduce the proof size by sharing fixed columns
        // between the ECC and Poseidon chips.
        // TODO: For multiple invocations they could/should be configured in
        // parallel rather than sharing perhaps?
        let lagrange_coeffs = [
            meta.fixed_column(),
            meta.fixed_column(),
            meta.fixed_column(),
            meta.fixed_column(),
            meta.fixed_column(),
            meta.fixed_column(),
            meta.fixed_column(),
            meta.fixed_column(),
        ];
        let rc_a = lagrange_coeffs[2..5].try_into().unwrap();
        let rc_b = lagrange_coeffs[5..8].try_into().unwrap();

        // Also use the first Lagrange coefficient column for loading global constants.
        meta.enable_constant(lagrange_coeffs[0]);

        // Use one of the right-most advice columns for all of our range checks.
        let range_check = LookupRangeCheckConfig::configure(meta, advices[9], table_idx);

        // Configuration for curve point operations.
        // This uses 10 advice columns and spans the whole circuit.
        let ecc_config = EccChip::<OrchardFixedBases>::configure(
            meta,
            advices,
            lagrange_coeffs,
            range_check.clone(),
        );

        // Configuration for the Poseidon hash
        let poseidon_config = PoseidonChip::configure(
            meta,
            P128Pow5T3,
            advices[6..9].try_into().unwrap(),
            advices[5],
            rc_a,
            rc_b,
        );

        // Configuration for a Sinsemilla hash instantiation and a
        // Merkle hash instantiation using this Sinsemilla instance.
        // Since the Sinsemilla config uses only 5 advice columns,
        // we can fit two instances side-by-side.
        let (sinsemilla_config_1, merkle_config_1) = {
            let sinsemilla_config_1 = SinsemillaChip::configure(
                meta,
                advices[..5].try_into().unwrap(),
                advices[6],
                lagrange_coeffs[0],
                lookup,
                range_check.clone(),
            );
            let merkle_config_1 = MerkleChip::configure(meta, sinsemilla_config_1.clone());
            (sinsemilla_config_1, merkle_config_1)
        };

        // Configuration for a Sinsemilla hash instantiation and a
        // Merkle hash instantiation using this Sinsemilla instance.
        // Since the Sinsemilla config uses only 5 advice columns,
        // we can fit two instances side-by-side.
        let (sinsemilla_config_2, merkle_config_2) = {
            let sinsemilla_config_2 = SinsemillaChip::configure(
                meta,
                advices[5..].try_into().unwrap(),
                advices[7],
                lagrange_coeffs[1],
                lookup,
                range_check,
            );
            let merkle_config_2 = MerkleChip::configure(meta, sinsemilla_config_2.clone());

            (sinsemilla_config_2, merkle_config_2)
        };

        SpendConfig {
            primary,
            advices,
            ecc_config,
            merkle_config_1,
            merkle_config_2,
            sinsemilla_config_1,
            sinsemilla_config_2,
            poseidon_config,
        }
    }

    fn synthesize(
        &self,
        config: Self::Config,
        mut layouter: impl Layouter<pallas::Base>,
    ) -> Result<(), Error> {
        // Load the Sinsemilla generator lookup table used by the whole circuit.
        SinsemillaChip::load(config.sinsemilla_config_1.clone(), &mut layouter)?;

        // Construct the ECC chip.
        let ecc_chip = config.ecc_chip();

        // Construct the merkle chips
        let merkle_chip_1 = config.merkle_chip_1();
        let merkle_chip_2 = config.merkle_chip_2();

        // =========
        // Nullifier
        // =========
        let secret_key = self.load_private(
            layouter.namespace(|| "load sinsemilla(secret key)"),
            config.advices[0],
            self.secret_key,
        )?;

        let serial = self.load_private(
            layouter.namespace(|| "load serial"),
            config.advices[0],
            self.serial,
        )?;

        let hash = {
            let poseidon_message = [secret_key, serial];

            let poseidon_hasher = PoseidonHash::<_, _, P128Pow5T3, _, 3, 2>::init(
                config.poseidon_chip(),
                layouter.namespace(|| "Poseidon init"),
                ConstantLength::<2>,
            )?;

            let poseidon_output =
                poseidon_hasher.hash(layouter.namespace(|| "Poseidon hash"), poseidon_message)?;

            let poseidon_output: CellValue<pallas::Base> = poseidon_output.inner().into();
            poseidon_output
        };

        layouter.constrain_instance(hash.cell(), config.primary, BURN_NULLIFIER_OFFSET)?;

        // let nullifier_k = FixedPointBaseField::from_inner(ecc_chip.clone(), NullifierK);
        //     nullifier_k.mul(
        //         layouter.namespace(|| "[poseidon_output + psi_old] NullifierK"),
        //         scalar,
        //     )?

        let value =
            self.load_private(layouter.namespace(|| "load value"), config.advices[0], self.value)?;

        let token =
            self.load_private(layouter.namespace(|| "load token"), config.advices[0], self.token)?;

        let coin_blind = self.load_private(
            layouter.namespace(|| "load coin_blind"),
            config.advices[0],
            self.coin_blind,
        )?;

        let public_key = {
            let nullifier_k = OrchardFixedBases::NullifierK;
            let nullifier_k = FixedPoint::from_inner(ecc_chip.clone(), nullifier_k);
            nullifier_k.mul_base_field(layouter.namespace(|| "[x_s] Nullifier"), secret_key)?
        };

        let (pub_x, pub_y) = (public_key.inner().x(), public_key.inner().y());

        // =========
        // Coin hash
        // =========
        let coin = {
            let poseidon_message = [pub_x, pub_y, value, token, serial, coin_blind];

            let poseidon_hasher = PoseidonHash::<_, _, P128Pow5T3, _, 3, 2>::init(
                config.poseidon_chip(),
                layouter.namespace(|| "Poseidon init"),
                ConstantLength::<6>,
            )?;

            let poseidon_output =
                poseidon_hasher.hash(layouter.namespace(|| "Poseidon hash"), poseidon_message)?;

            let poseidon_output: CellValue<pallas::Base> = poseidon_output.inner().into();
            poseidon_output
        };

        // ===========
        // Merkle root
        // ===========

        let path = MerklePath {
            chip_1: merkle_chip_1,
            chip_2: merkle_chip_2,
            domain: OrchardHashDomains::MerkleCrh,
            leaf_pos: self.leaf_pos,
            path: self.merkle_path,
        };

        let computed_final_root =
            path.calculate_root(layouter.namespace(|| "calculate root"), coin)?;

        layouter.constrain_instance(
            computed_final_root.cell(),
            config.primary,
            BURN_MERKLEROOT_OFFSET,
        )?;

        // ================
        // Value commitment
        // ================

        // This constant one is used for multiplication
        let one = self.load_private(
            layouter.namespace(|| "load constant one"),
            config.advices[0],
            Some(pallas::Base::one()),
        )?;

        let value =
            self.load_private(layouter.namespace(|| "load value"), config.advices[0], self.value)?;

        // v * G_1
        let (commitment, _) = {
            let value_commit_v = OrchardFixedBases::ValueCommitV;
            let value_commit_v = FixedPoint::from_inner(ecc_chip.clone(), value_commit_v);
            value_commit_v.mul_short(layouter.namespace(|| "[value] ValueCommitV"), (value, one))?
        };

        // r_V * G_2
        let (blind, _rcv) = {
            let rcv = self.value_blind;
            let value_commit_r = OrchardFixedBases::ValueCommitR;
            let value_commit_r = FixedPoint::from_inner(ecc_chip.clone(), value_commit_r);
            value_commit_r.mul(layouter.namespace(|| "[value_blind] ValueCommitR"), rcv)?
        };

        // Constrain the value commitment coordinates
        let value_commit = commitment.add(layouter.namespace(|| "valuecommit"), &blind)?;
        layouter.constrain_instance(
            value_commit.inner().x().cell(),
            config.primary,
            BURN_VALCOMX_OFFSET,
        )?;
        layouter.constrain_instance(
            value_commit.inner().y().cell(),
            config.primary,
            BURN_VALCOMY_OFFSET,
        )?;

        // ================
        // Token commitment
        // ================

        let token =
            self.load_private(layouter.namespace(|| "load token"), config.advices[0], self.token)?;

        // a * G_1
        let (commitment, _) = {
            let token_commit_v = OrchardFixedBases::ValueCommitV;
            let token_commit_v = FixedPoint::from_inner(ecc_chip.clone(), token_commit_v);
            token_commit_v.mul_short(layouter.namespace(|| "[token] ValueCommitV"), (token, one))?
        };

        // r_A * G_2
        let (blind, _rca) = {
            let rca = self.token_blind;
            let token_commit_r = OrchardFixedBases::ValueCommitR;
            let token_commit_r = FixedPoint::from_inner(ecc_chip.clone(), token_commit_r);
            token_commit_r.mul(layouter.namespace(|| "[token_blind] ValueCommitR"), rca)?
        };

        // Constrain the token commitment coordinates
        let token_commit = commitment.add(layouter.namespace(|| "tokencommit"), &blind)?;

        layouter.constrain_instance(
            token_commit.inner().x().cell(),
            config.primary,
            BURN_TOKCOMX_OFFSET,
        )?;

        layouter.constrain_instance(
            token_commit.inner().y().cell(),
            config.primary,
            BURN_TOKCOMY_OFFSET,
        )?;

        // ========================
        // Signature key derivation
        // ========================
        let sig_secret = self.load_private(
            layouter.namespace(|| "load sig_secret"),
            config.advices[0],
            self.sig_secret,
        )?;

        let sig_pub = {
            let nullifier_k = OrchardFixedBases::NullifierK;
            let nullifier_k = FixedPoint::from_inner(ecc_chip, nullifier_k);
            nullifier_k.mul_base_field(layouter.namespace(|| "[x_s] Nullifier"), sig_secret)?
        };

        layouter.constrain_instance(
            sig_pub.inner().x().cell(),
            config.primary,
            BURN_SIGKEYX_OFFSET,
        )?;
        layouter.constrain_instance(
            sig_pub.inner().y().cell(),
            config.primary,
            BURN_SIGKEYY_OFFSET,
        )?;

        // At this point we've enforced all of our public inputs.
        Ok(())
    }
}