taceo-circom-types 0.2.5

//Copyright (c) 2021 Georgios Konstantopoulos
//
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//! This module defines the [`Zkey`] struct that implements deserialization of Circom zkey files via [`Zkey::from_reader`].
use ark_ec::pairing::Pairing;
use ark_ff::PrimeField;
use ark_poly::{Polynomial, univariate::DensePolynomial};
use ark_serde_compat::CheckElement;
use ark_serialize::CanonicalDeserialize;
use std::io::{Cursor, Read};

use crate::{
    binfile::{BinFile, ZkeyParserError, ZkeyParserResult},
    traits::CircomArkworksPairingBridge,
};

macro_rules! u32_to_usize {
    ($x: expr) => {
        usize::try_from($x).expect("u32 fits into usize")
    };
}

/// Represents a zkey in the format defined by Circom. Implements [`Zkey::from_reader`] to deserialize a zkey from a reader.
#[derive(Clone)]
pub struct Zkey<P: Pairing> {
    /// The amount of vars in the circuit
    pub n_vars: usize,
    /// The amount of public values in the circuit
    pub n_public: usize,
    /// The domain size (power of two)
    pub domain_size: usize,
    /// ld(domain size)
    pub pow: usize,
    /// The amounts of additions
    pub n_additions: usize,
    /// The amounts of constraints
    pub n_constraints: usize,
    /// The verifying key
    pub verifying_key: VerifyingKey<P>,
    /// The indices of the additions of the witness and their respective blinding factors
    pub additions: Vec<Additions<P>>,
    /// The witness indices of the signals of wire mapping a
    pub map_a: Vec<usize>,
    /// The witness indices of the signals of wire mapping b
    pub map_b: Vec<usize>,
    /// The witness indices of the signals of wire mapping c
    pub map_c: Vec<usize>,
    /// Qm polynomial
    pub qm_poly: CircomPolynomial<P::ScalarField>,
    /// Ql polynomial
    pub ql_poly: CircomPolynomial<P::ScalarField>,
    /// Qr polynomial
    pub qr_poly: CircomPolynomial<P::ScalarField>,
    /// Qo polynomial
    pub qo_poly: CircomPolynomial<P::ScalarField>,
    /// Qc polynomial
    pub qc_poly: CircomPolynomial<P::ScalarField>,
    /// σ1 polynomial
    pub s1_poly: CircomPolynomial<P::ScalarField>,
    /// σ2 polynomial
    pub s2_poly: CircomPolynomial<P::ScalarField>,
    /// σ3 polynomial
    pub s3_poly: CircomPolynomial<P::ScalarField>,
    /// Lagrange polynomials. One [Polynomial] for each public input.
    pub lagrange: Vec<CircomPolynomial<P::ScalarField>>,
    /// The powers of 𝜏
    pub p_tau: Vec<P::G1Affine>,
}

/// A polynomial in coefficient and evaluation form for PLONK's [Zkey].
#[derive(Clone)]
pub struct CircomPolynomial<F: PrimeField> {
    /// The polynomial's coefficient form
    pub coeffs: DensePolynomial<F>,
    /// The polynomial's evaluation form
    pub evaluations: Vec<F>,
}

impl<F: PrimeField> CircomPolynomial<F> {
    /// Evaluates the polynomial at a certain point
    pub fn evaluate(&self, point: &F) -> F {
        self.coeffs.evaluate(point)
    }
}

#[derive(Clone)]
/// The indices and blinding factors for all additions necessary during a PLONK proof. The id's represent the index
/// in the witness.
pub struct Additions<P: Pairing> {
    /// The index of lhs
    pub signal_id1: u32,
    /// The index of rhs
    pub signal_id2: u32,
    /// The blinding factor of lhs
    pub factor1: P::ScalarField,
    /// The blinding factor of rhs
    pub factor2: P::ScalarField,
}

/// The verifying key for a PLONK proof.
#[derive(Default, Clone, Debug)]
pub struct VerifyingKey<P: Pairing> {
    /// k1
    pub k1: P::ScalarField,
    /// k2
    pub k2: P::ScalarField,
    /// The evaluation of [`Zkey::qm_poly`] with [`Zkey::p_tau`]
    pub qm: P::G1Affine,
    /// The evaluation of [`Zkey::qr_poly`] with [`Zkey::p_tau`]
    pub ql: P::G1Affine,
    /// The evaluation of [`Zkey::ql_poly`] with [`Zkey::p_tau`]
    pub qr: P::G1Affine,
    /// The evaluation of [`Zkey::qo_poly`] with [`Zkey::p_tau`]
    pub qo: P::G1Affine,
    /// The evaluation of [`Zkey::qc_poly`] with [`Zkey::p_tau`]
    pub qc: P::G1Affine,
    /// The evaluation of [`Zkey::s1_poly`] with [`Zkey::p_tau`]
    pub s1: P::G1Affine,
    /// The evaluation of [`Zkey::s2_poly`] with [`Zkey::p_tau`]
    pub s2: P::G1Affine,
    /// The evaluation of [`Zkey::s3_poly`] with [`Zkey::p_tau`]
    pub s3: P::G1Affine,
    /// x_2
    pub x_2: P::G2Affine,
}

impl<P: Pairing + CircomArkworksPairingBridge> Zkey<P> {
    /// Deserializes a [`Zkey`] from a reader.
    ///
    /// You may use the second parameter to specify whether
    /// the deserialization should check if the elements are on
    /// their respective curve.
    ///
    /// `No` indicates to skip those checks, which is by orders of magnitude
    /// faster, but could potentially result in undefined behaviour. Use
    /// only with care.
    ///
    /// See [`CheckElement`].
    pub fn from_reader<R: Read>(mut reader: R, check: CheckElement) -> ZkeyParserResult<Self> {
        let mut binfile = BinFile::<P>::new(&mut reader)?;

        tracing::debug!("start transforming bin file into zkey...");
        let header = PlonkHeader::<P>::read(&mut binfile.take_section(2))?;
        let n_vars = header.n_vars;
        let n_additions = header.n_additions;
        let n_constraints = header.n_constraints;
        let n_public = header.n_public;
        let domain_size = header.domain_size;
        //the sigmas are in the same section - so we split it here in separate chunks
        let sigma_section_size = domain_size * header.n8r + domain_size * 4 * header.n8r;

        let add_section = binfile.take_section(3);
        let a_section = binfile.take_section(4);
        let b_section = binfile.take_section(5);
        let c_section = binfile.take_section(6);
        let qm_section = binfile.take_section(7);
        let ql_section = binfile.take_section(8);
        let qr_section = binfile.take_section(9);
        let q0_section = binfile.take_section(10);
        let qc_section = binfile.take_section(11);
        let sigma_sections = binfile.take_section_raw(12);
        let l_section = binfile.take_section(13);
        let t_section = binfile.take_section(14);
        let sigma1_section = Cursor::new(&sigma_sections[..sigma_section_size]);
        let sigma2_section =
            Cursor::new(&sigma_sections[sigma_section_size..sigma_section_size * 2]);
        let sigma3_section = Cursor::new(&sigma_sections[sigma_section_size * 2..]);

        let mut additions = None;
        let mut map_a = None;
        let mut map_b = None;
        let mut map_c = None;
        let mut qm = None;
        let mut ql = None;
        let mut qr = None;
        let mut q0 = None;
        let mut qc = None;
        let mut sigma1 = None;
        let mut sigma2 = None;
        let mut sigma3 = None;
        let mut lagrange = None;
        let mut p_tau = None;
        tracing::debug!("parsing zkey sections...");
        std::thread::scope(|s| {
            s.spawn(|| additions = Some(Self::additions_indices(n_additions, add_section)));
            s.spawn(|| map_a = Some(Self::id_map(n_constraints, a_section)));
            s.spawn(|| map_b = Some(Self::id_map(n_constraints, b_section)));
            s.spawn(|| map_c = Some(Self::id_map(n_constraints, c_section)));
            s.spawn(|| qm = Some(Self::evaluations(domain_size, qm_section)));
            s.spawn(|| ql = Some(Self::evaluations(domain_size, ql_section)));
            s.spawn(|| qr = Some(Self::evaluations(domain_size, qr_section)));
            s.spawn(|| q0 = Some(Self::evaluations(domain_size, q0_section)));
            s.spawn(|| qc = Some(Self::evaluations(domain_size, qc_section)));
            s.spawn(|| sigma1 = Some(Self::evaluations(domain_size, sigma1_section)));
            s.spawn(|| sigma2 = Some(Self::evaluations(domain_size, sigma2_section)));
            s.spawn(|| sigma3 = Some(Self::evaluations(domain_size, sigma3_section)));
            s.spawn(|| lagrange = Some(Self::lagrange(n_public, domain_size, l_section)));
            s.spawn(|| p_tau = Some(Self::taus(domain_size, t_section, check)));
        });
        tracing::debug!("we are done with parsing sections!");
        Ok(Self {
            n_vars,
            n_public,
            domain_size,
            pow: header.power,
            n_additions,
            n_constraints,
            verifying_key: header.verifying_key,
            //we unwrap all elements here, as we know they have to be Some.
            //Even on the error case, we then have a Some value
            additions: additions.unwrap()?,
            map_a: map_a.unwrap()?,
            map_b: map_b.unwrap()?,
            map_c: map_c.unwrap()?,
            qm_poly: qm.unwrap()?,
            ql_poly: ql.unwrap()?,
            qr_poly: qr.unwrap()?,
            qo_poly: q0.unwrap()?,
            qc_poly: qc.unwrap()?,
            s1_poly: sigma1.unwrap()?,
            s2_poly: sigma2.unwrap()?,
            s3_poly: sigma3.unwrap()?,
            lagrange: lagrange.unwrap()?,
            p_tau: p_tau.unwrap()?,
        })
    }

    fn additions_indices<R: Read>(
        n_additions: usize,
        mut reader: R,
    ) -> ZkeyParserResult<Vec<Additions<P>>> {
        let mut additions = Vec::with_capacity(n_additions);
        for _ in 0..n_additions {
            let signal_id1 = u32::deserialize_uncompressed(&mut reader)?;
            let signal_id2 = u32::deserialize_uncompressed(&mut reader)?;
            let factor1 = P::fr_from_montgomery_reader(&mut reader)?;
            let factor2 = P::fr_from_montgomery_reader(&mut reader)?;
            additions.push(Additions {
                signal_id1,
                signal_id2,
                factor1,
                factor2,
            })
        }
        Ok(additions)
    }

    fn id_map<R: Read>(n_constraints: usize, mut reader: R) -> ZkeyParserResult<Vec<usize>> {
        let mut map = Vec::with_capacity(n_constraints);
        for _ in 0..n_constraints {
            map.push(u32_to_usize!(u32::deserialize_uncompressed(&mut reader)?));
        }
        Ok(map)
    }

    fn evaluations<R: Read>(
        domain_size: usize,
        mut reader: R,
    ) -> ZkeyParserResult<CircomPolynomial<P::ScalarField>> {
        let mut coeffs = Vec::with_capacity(domain_size);
        for _ in 0..domain_size {
            coeffs.push(P::fr_from_montgomery_reader(&mut reader)?);
        }

        let mut evaluations = Vec::with_capacity(domain_size * 4);
        for _ in 0..domain_size * 4 {
            evaluations.push(P::fr_from_montgomery_reader(&mut reader)?);
        }
        Ok(CircomPolynomial {
            coeffs: DensePolynomial { coeffs },
            evaluations,
        })
    }

    fn lagrange<R: Read>(
        n_public: usize,
        domain_size: usize,
        mut reader: R,
    ) -> ZkeyParserResult<Vec<CircomPolynomial<P::ScalarField>>> {
        let mut lagrange = Vec::with_capacity(n_public);
        for _ in 0..n_public {
            lagrange.push(Self::evaluations(domain_size, &mut reader)?);
        }
        Ok(lagrange)
    }

    fn taus<R: Read>(
        domain_size: usize,
        reader: R,
        check: CheckElement,
    ) -> ZkeyParserResult<Vec<P::G1Affine>> {
        // //TODO: why domain size + 6?
        Ok(P::g1_vec_from_reader(reader, domain_size + 6, check)?)
    }
}

impl<P: Pairing + CircomArkworksPairingBridge> VerifyingKey<P> {
    fn new<R: Read>(mut reader: R) -> ZkeyParserResult<Self> {
        let k1 = P::fr_from_montgomery_reader(&mut reader)?;
        let k2 = P::fr_from_montgomery_reader(&mut reader)?;
        let qm = P::g1_from_reader(&mut reader, CheckElement::Yes)?;
        let ql = P::g1_from_reader(&mut reader, CheckElement::Yes)?;
        let qr = P::g1_from_reader(&mut reader, CheckElement::Yes)?;
        let qo = P::g1_from_reader(&mut reader, CheckElement::Yes)?;
        let qc = P::g1_from_reader(&mut reader, CheckElement::Yes)?;
        let s1 = P::g1_from_reader(&mut reader, CheckElement::Yes)?;
        let s2 = P::g1_from_reader(&mut reader, CheckElement::Yes)?;
        let s3 = P::g1_from_reader(&mut reader, CheckElement::Yes)?;
        let x2 = P::g2_from_reader(&mut reader, CheckElement::Yes)?;

        Ok(Self {
            k1,
            k2,
            qm,
            ql,
            qr,
            qo,
            qc,
            s1,
            s2,
            s3,
            x_2: x2,
        })
    }
}

#[derive(Clone)]
struct PlonkHeader<P: Pairing> {
    n8r: usize,
    n_vars: usize,
    n_public: usize,
    domain_size: usize,
    power: usize,
    n_additions: usize,
    n_constraints: usize,
    verifying_key: VerifyingKey<P>,
}

impl<P: Pairing + CircomArkworksPairingBridge> PlonkHeader<P> {
    fn read<R: Read>(mut reader: &mut R) -> ZkeyParserResult<Self> {
        let n8q = u32::deserialize_uncompressed(&mut reader)?;
        //modulus of BaseField
        let q = <P::BaseField as PrimeField>::BigInt::deserialize_uncompressed(&mut reader)?;
        let expected_n8q = P::BaseField::MODULUS_BIT_SIZE.div_ceil(8);
        tracing::debug!("base field byte size: {n8q}");
        if n8q != expected_n8q {
            return Err(ZkeyParserError::UnexpectedByteSize(expected_n8q, n8q));
        }
        let modulus = <P::BaseField as PrimeField>::MODULUS;
        if q != modulus {
            return Err(ZkeyParserError::InvalidPrimeInHeader);
        }
        let n8r = u32::deserialize_uncompressed(&mut reader)?;
        //modulus of ScalarField
        let r = <P::ScalarField as PrimeField>::BigInt::deserialize_uncompressed(&mut reader)?;
        tracing::debug!("scalar field byte size: {n8r}");
        let expected_n8r = P::ScalarField::MODULUS_BIT_SIZE.div_ceil(8);
        if n8r != expected_n8r {
            return Err(ZkeyParserError::UnexpectedByteSize(expected_n8r, n8r));
        }

        let n8r = usize::try_from(n8r).expect("works after check");
        let modulus = <P::ScalarField as PrimeField>::MODULUS;
        if r != modulus {
            return Err(ZkeyParserError::InvalidPrimeInHeader);
        }
        let n_vars = u32::deserialize_uncompressed(&mut reader)?;
        let n_public = u32::deserialize_uncompressed(&mut reader)?;
        let domain_size = u32::deserialize_uncompressed(&mut reader)?;
        let n_additions = u32::deserialize_uncompressed(&mut reader)?;
        let n_constraints = u32::deserialize_uncompressed(&mut reader)?;
        tracing::debug!("n_vars: {n_vars}; n_public: {n_public}, domain_size: {domain_size}");
        let verifying_key = VerifyingKey::new(&mut reader)?;
        if domain_size & (domain_size - 1) == 0 && domain_size > 0 {
            tracing::debug!("read header done!");
            Ok(Self {
                n8r,
                n_vars: u32_to_usize!(n_vars),
                n_public: u32_to_usize!(n_public),
                domain_size: u32_to_usize!(domain_size),
                power: u32_to_usize!(domain_size.ilog2()),
                n_additions: u32_to_usize!(n_additions),
                n_constraints: u32_to_usize!(n_constraints),
                verifying_key,
            })
        } else {
            Err(ZkeyParserError::CorruptedBinFile(format!(
                "Invalid domain size {domain_size}. Must be power of 2"
            )))
        }
    }
}