halo2curves_axiom/bls12_381/hash_to_curve/
map_g2.rs

//! Implementation of hash-to-curve for the G2 group
//!
//! Source: <https://github.com/privacy-scaling-explorations/bls12_381>

use subtle::{Choice, ConditionallyNegatable, ConditionallySelectable, ConstantTimeEq};

use super::chain::chain_p2m9div16;
use super::{HashToField, MapToCurve, Sgn0};
use crate::bls12_381::generic_array::{
    typenum::{U128, U64},
    GenericArray,
};
use crate::bls12_381::{fp::Fp, fp2::Fp2, g2::G2Projective};
use ff::Field;

/// Coefficients of the 3-isogeny x map's numerator
const ISO3_XNUM: [Fp2; 4] = [
    Fp2 {
        c0: Fp::from_raw_unchecked([
            0x47f6_71c7_1ce0_5e62,
            0x06dd_5707_1206_393e,
            0x7c80_cd2a_f3fd_71a2,
            0x0481_03ea_9e6c_d062,
            0xc545_16ac_c8d0_37f6,
            0x1380_8f55_0920_ea41,
        ]),
        c1: Fp::from_raw_unchecked([
            0x47f6_71c7_1ce0_5e62,
            0x06dd_5707_1206_393e,
            0x7c80_cd2a_f3fd_71a2,
            0x0481_03ea_9e6c_d062,
            0xc545_16ac_c8d0_37f6,
            0x1380_8f55_0920_ea41,
        ]),
    },
    Fp2 {
        c0: Fp::zero(),
        c1: Fp::from_raw_unchecked([
            0x5fe5_5555_554c_71d0,
            0x873f_ffdd_236a_aaa3,
            0x6a6b_4619_b26e_f918,
            0x21c2_8884_0887_4945,
            0x2836_cda7_028c_abc5,
            0x0ac7_3310_a7fd_5abd,
        ]),
    },
    Fp2 {
        c0: Fp::from_raw_unchecked([
            0x0a0c_5555_5559_71c3,
            0xdb0c_0010_1f9e_aaae,
            0xb1fb_2f94_1d79_7997,
            0xd396_0742_ef41_6e1c,
            0xb700_40e2_c205_56f4,
            0x149d_7861_e581_393b,
        ]),
        c1: Fp::from_raw_unchecked([
            0xaff2_aaaa_aaa6_38e8,
            0x439f_ffee_91b5_5551,
            0xb535_a30c_d937_7c8c,
            0x90e1_4442_0443_a4a2,
            0x941b_66d3_8146_55e2,
            0x0563_9988_53fe_ad5e,
        ]),
    },
    Fp2 {
        c0: Fp::from_raw_unchecked([
            0x40aa_c71c_71c7_25ed,
            0x1909_5555_7a84_e38e,
            0xd817_050a_8f41_abc3,
            0xd864_85d4_c87f_6fb1,
            0x696e_b479_f885_d059,
            0x198e_1a74_3280_02d2,
        ]),
        c1: Fp::zero(),
    },
];

/// Coefficients of the 3-isogeny x map's denominator
const ISO3_XDEN: [Fp2; 3] = [
    Fp2 {
        c0: Fp::zero(),
        c1: Fp::from_raw_unchecked([
            0x1f3a_ffff_ff13_ab97,
            0xf25b_fc61_1da3_ff3e,
            0xca37_57cb_3819_b208,
            0x3e64_2736_6f8c_ec18,
            0x0397_7bc8_6095_b089,
            0x04f6_9db1_3f39_a952,
        ]),
    },
    Fp2 {
        c0: Fp::from_raw_unchecked([
            0x4476_0000_0027_552e,
            0xdcb8_009a_4348_0020,
            0x6f7e_e9ce_4a6e_8b59,
            0xb103_30b7_c0a9_5bc6,
            0x6140_b1fc_fb1e_54b7,
            0x0381_be09_7f0b_b4e1,
        ]),
        c1: Fp::from_raw_unchecked([
            0x7588_ffff_ffd8_557d,
            0x41f3_ff64_6e0b_ffdf,
            0xf7b1_e8d2_ac42_6aca,
            0xb374_1acd_32db_b6f8,
            0xe9da_f5b9_482d_581f,
            0x167f_53e0_ba74_31b8,
        ]),
    },
    Fp2::one(),
];

/// Coefficients of the 3-isogeny y map's numerator
const ISO3_YNUM: [Fp2; 4] = [
    Fp2 {
        c0: Fp::from_raw_unchecked([
            0x96d8_f684_bdfc_77be,
            0xb530_e4f4_3b66_d0e2,
            0x184a_88ff_3796_52fd,
            0x57cb_23ec_fae8_04e1,
            0x0fd2_e39e_ada3_eba9,
            0x08c8_055e_31c5_d5c3,
        ]),
        c1: Fp::from_raw_unchecked([
            0x96d8_f684_bdfc_77be,
            0xb530_e4f4_3b66_d0e2,
            0x184a_88ff_3796_52fd,
            0x57cb_23ec_fae8_04e1,
            0x0fd2_e39e_ada3_eba9,
            0x08c8_055e_31c5_d5c3,
        ]),
    },
    Fp2 {
        c0: Fp::zero(),
        c1: Fp::from_raw_unchecked([
            0xbf0a_71c7_1c91_b406,
            0x4d6d_55d2_8b76_38fd,
            0x9d82_f98e_5f20_5aee,
            0xa27a_a27b_1d1a_18d5,
            0x02c3_b2b2_d293_8e86,
            0x0c7d_1342_0b09_807f,
        ]),
    },
    Fp2 {
        c0: Fp::from_raw_unchecked([
            0xd7f9_5555_5553_1c74,
            0x21cf_fff7_48da_aaa8,
            0x5a9a_d186_6c9b_be46,
            0x4870_a221_0221_d251,
            0x4a0d_b369_c0a3_2af1,
            0x02b1_ccc4_29ff_56af,
        ]),
        c1: Fp::from_raw_unchecked([
            0xe205_aaaa_aaac_8e37,
            0xfcdc_0007_6879_5556,
            0x0c96_011a_8a15_37dd,
            0x1c06_a963_f163_406e,
            0x010d_f44c_82a8_81e6,
            0x174f_4526_0f80_8feb,
        ]),
    },
    Fp2 {
        c0: Fp::from_raw_unchecked([
            0xa470_bda1_2f67_f35c,
            0xc0fe_38e2_3327_b425,
            0xc9d3_d0f2_c6f0_678d,
            0x1c55_c993_5b5a_982e,
            0x27f6_c0e2_f074_6764,
            0x117c_5e6e_28aa_9054,
        ]),
        c1: Fp::zero(),
    },
];

/// Coefficients of the 3-isogeny y map's denominator
const ISO3_YDEN: [Fp2; 4] = [
    Fp2 {
        c0: Fp::from_raw_unchecked([
            0x0162_ffff_fa76_5adf,
            0x8f7b_ea48_0083_fb75,
            0x561b_3c22_59e9_3611,
            0x11e1_9fc1_a9c8_75d5,
            0xca71_3efc_0036_7660,
            0x03c6_a03d_41da_1151,
        ]),
        c1: Fp::from_raw_unchecked([
            0x0162_ffff_fa76_5adf,
            0x8f7b_ea48_0083_fb75,
            0x561b_3c22_59e9_3611,
            0x11e1_9fc1_a9c8_75d5,
            0xca71_3efc_0036_7660,
            0x03c6_a03d_41da_1151,
        ]),
    },
    Fp2 {
        c0: Fp::zero(),
        c1: Fp::from_raw_unchecked([
            0x5db0_ffff_fd3b_02c5,
            0xd713_f523_58eb_fdba,
            0x5ea6_0761_a84d_161a,
            0xbb2c_75a3_4ea6_c44a,
            0x0ac6_7359_21c1_119b,
            0x0ee3_d913_bdac_fbf6,
        ]),
    },
    Fp2 {
        c0: Fp::from_raw_unchecked([
            0x66b1_0000_003a_ffc5,
            0xcb14_00e7_64ec_0030,
            0xa73e_5eb5_6fa5_d106,
            0x8984_c913_a0fe_09a9,
            0x11e1_0afb_78ad_7f13,
            0x0542_9d0e_3e91_8f52,
        ]),
        c1: Fp::from_raw_unchecked([
            0x534d_ffff_ffc4_aae6,
            0x5397_ff17_4c67_ffcf,
            0xbff2_73eb_870b_251d,
            0xdaf2_8271_5287_0915,
            0x393a_9cba_ca9e_2dc3,
            0x14be_74db_faee_5748,
        ]),
    },
    Fp2::one(),
];

const SSWU_ELLP_A: Fp2 = Fp2 {
    c0: Fp::zero(),
    c1: Fp::from_raw_unchecked([
        0xe53a_0000_0313_5242,
        0x0108_0c0f_def8_0285,
        0xe788_9edb_e340_f6bd,
        0x0b51_3751_2631_0601,
        0x02d6_9857_17c7_44ab,
        0x1220_b4e9_79ea_5467,
    ]),
};

const SSWU_ELLP_B: Fp2 = Fp2 {
    c0: Fp::from_raw_unchecked([
        0x22ea_0000_0cf8_9db2,
        0x6ec8_32df_7138_0aa4,
        0x6e1b_9440_3db5_a66e,
        0x75bf_3c53_a794_73ba,
        0x3dd3_a569_412c_0a34,
        0x125c_db5e_74dc_4fd1,
    ]),
    c1: Fp::from_raw_unchecked([
        0x22ea_0000_0cf8_9db2,
        0x6ec8_32df_7138_0aa4,
        0x6e1b_9440_3db5_a66e,
        0x75bf_3c53_a794_73ba,
        0x3dd3_a569_412c_0a34,
        0x125c_db5e_74dc_4fd1,
    ]),
};

const SSWU_XI: Fp2 = Fp2 {
    c0: Fp::from_raw_unchecked([
        0x87eb_ffff_fff9_555c,
        0x656f_ffe5_da8f_fffa,
        0x0fd0_7493_45d3_3ad2,
        0xd951_e663_0665_76f4,
        0xde29_1a3d_41e9_80d3,
        0x0815_664c_7dfe_040d,
    ]),
    c1: Fp::from_raw_unchecked([
        0x43f5_ffff_fffc_aaae,
        0x32b7_fff2_ed47_fffd,
        0x07e8_3a49_a2e9_9d69,
        0xeca8_f331_8332_bb7a,
        0xef14_8d1e_a0f4_c069,
        0x040a_b326_3eff_0206,
    ]),
};

const SSWU_ETAS: [Fp2; 4] = [
    Fp2 {
        c0: Fp::from_raw_unchecked([
            0x05e5_1466_8ac7_36d2,
            0x9089_b4d6_b84f_3ea5,
            0x603c_384c_224a_8b32,
            0xf325_7909_536a_fea6,
            0x5c5c_dbab_ae65_6d81,
            0x075b_fa08_63c9_87e9,
        ]),
        c1: Fp::from_raw_unchecked([
            0x338d_9bfe_0808_7330,
            0x7b8e_48b2_bd83_cefe,
            0x530d_ad5d_306b_5be7,
            0x5a4d_7e8e_6c40_8b6d,
            0x6258_f7a6_232c_ab9b,
            0x0b98_5811_cce1_4db5,
        ]),
    },
    Fp2 {
        c0: Fp::from_raw_unchecked([
            0x8671_6401_f7f7_377b,
            0xa31d_b74b_f3d0_3101,
            0x1423_2543_c645_9a3c,
            0x0a29_ccf6_8744_8752,
            0xe8c2_b010_201f_013c,
            0x0e68_b9d8_6c9e_98e4,
        ]),
        c1: Fp::from_raw_unchecked([
            0x05e5_1466_8ac7_36d2,
            0x9089_b4d6_b84f_3ea5,
            0x603c_384c_224a_8b32,
            0xf325_7909_536a_fea6,
            0x5c5c_dbab_ae65_6d81,
            0x075b_fa08_63c9_87e9,
        ]),
    },
    Fp2 {
        c0: Fp::from_raw_unchecked([
            0x718f_dad2_4ee1_d90f,
            0xa58c_025b_ed82_76af,
            0x0c3a_1023_0ab7_976f,
            0xf0c5_4df5_c8f2_75e1,
            0x4ec2_478c_28ba_f465,
            0x1129_373a_90c5_08e6,
        ]),
        c1: Fp::from_raw_unchecked([
            0x019a_f5f9_80a3_680c,
            0x4ed7_da0e_6606_3afa,
            0x6003_5472_3b5d_9972,
            0x8b2f_958b_20d0_9d72,
            0x0474_938f_02d4_61db,
            0x0dcf_8b9e_0684_ab1c,
        ]),
    },
    Fp2 {
        c0: Fp::from_raw_unchecked([
            0xb864_0a06_7f5c_429f,
            0xcfd4_25f0_4b4d_c505,
            0x072d_7e2e_bb53_5cb1,
            0xd947_b5f9_d2b4_754d,
            0x46a7_1427_4077_4afb,
            0x0c31_864c_32fb_3b7e,
        ]),
        c1: Fp::from_raw_unchecked([
            0x718f_dad2_4ee1_d90f,
            0xa58c_025b_ed82_76af,
            0x0c3a_1023_0ab7_976f,
            0xf0c5_4df5_c8f2_75e1,
            0x4ec2_478c_28ba_f465,
            0x1129_373a_90c5_08e6,
        ]),
    },
];

const SSWU_RV1: Fp2 = Fp2 {
    c0: Fp::from_raw_unchecked([
        0x7bcf_a7a2_5aa3_0fda,
        0xdc17_dec1_2a92_7e7c,
        0x2f08_8dd8_6b4e_bef1,
        0xd1ca_2087_da74_d4a7,
        0x2da2_5966_96ce_bc1d,
        0x0e2b_7eed_bbfd_87d2,
    ]),
    c1: Fp::from_raw_unchecked([
        0x7bcf_a7a2_5aa3_0fda,
        0xdc17_dec1_2a92_7e7c,
        0x2f08_8dd8_6b4e_bef1,
        0xd1ca_2087_da74_d4a7,
        0x2da2_5966_96ce_bc1d,
        0x0e2b_7eed_bbfd_87d2,
    ]),
};

impl HashToField for Fp2 {
    // ceil(log2(p)) = 381, m = 2, k = 128.
    type InputLength = U128;

    fn from_okm(okm: &GenericArray<u8, U128>) -> Fp2 {
        let c0 = <Fp as HashToField>::from_okm(GenericArray::<u8, U64>::from_slice(&okm[..64]));
        let c1 = <Fp as HashToField>::from_okm(GenericArray::<u8, U64>::from_slice(&okm[64..]));
        Fp2 { c0, c1 }
    }
}

impl Sgn0 for Fp2 {
    fn sgn0(&self) -> Choice {
        let sign_0 = self.c0.sgn0();
        let zero_0 = self.c0.is_zero();
        let sign_1 = self.c1.sgn0();
        sign_0 | (zero_0 & sign_1)
    }
}

/// Maps from an [`Fp2]` element to a point on iso-G2.
fn map_to_curve_simple_swu(u: &Fp2) -> G2Projective {
    let usq = u.square();
    let xi_usq = SSWU_XI * usq;
    let xisq_u4 = xi_usq.square();
    let nd_common = xisq_u4 + xi_usq; // XI^2 * u^4 + XI * u^2
    let x_den = SSWU_ELLP_A * Fp2::conditional_select(&(-nd_common), &SSWU_XI, nd_common.is_zero());
    let x0_num = SSWU_ELLP_B * (Fp2::one() + nd_common); // B * (1 + (XI^2 * u^4 + XI * u^2))

    // compute g(x0(u))
    let x_densq = x_den.square();
    let gx_den = x_densq * x_den;
    // x0_num^3 + A * x0_num * x_den^2 + B * x_den^3
    let gx0_num = (x0_num.square() + SSWU_ELLP_A * x_densq) * x0_num + SSWU_ELLP_B * gx_den;

    // compute g(x0(u)) ^ ((p^2 - 9) // 16)
    let sqrt_candidate = {
        let vsq = gx_den.square(); // v^2
        let v_3 = vsq * gx_den; // v^3
        let v_4 = vsq.square(); // v^4
        let uv_7 = gx0_num * v_3 * v_4; // u v^7
        let uv_15 = uv_7 * v_4.square(); // u v^15
        uv_7 * chain_p2m9div16(&uv_15) // u v^7 (u v^15) ^ ((p^2 - 9) // 16)
    };

    // set y = sqrt_candidate * Fp2::one(), check candidate against other roots of unity
    let mut y = sqrt_candidate;
    // check Fp2(0, 1)
    let tmp = Fp2 {
        c0: -sqrt_candidate.c1,
        c1: sqrt_candidate.c0,
    };
    y.conditional_assign(&tmp, (tmp.square() * gx_den).ct_eq(&gx0_num));
    // check Fp2(RV1, RV1)
    let tmp = sqrt_candidate * SSWU_RV1;
    y.conditional_assign(&tmp, (tmp.square() * gx_den).ct_eq(&gx0_num));
    // check Fp2(RV1, -RV1)
    let tmp = Fp2 {
        c0: tmp.c1,
        c1: -tmp.c0,
    };
    y.conditional_assign(&tmp, (tmp.square() * gx_den).ct_eq(&gx0_num));

    // compute g(x1(u)) = g(x0(u)) * XI^3 * u^6
    let gx1_num = gx0_num * xi_usq * xisq_u4;
    // compute g(x1(u)) * u^3
    let sqrt_candidate = sqrt_candidate * usq * u;
    let mut eta_found = Choice::from(0u8);
    for eta in &SSWU_ETAS[..] {
        let tmp = sqrt_candidate * eta;
        let found = (tmp.square() * gx_den).ct_eq(&gx1_num);
        y.conditional_assign(&tmp, found);
        eta_found |= found;
    }

    let x_num = Fp2::conditional_select(&x0_num, &(x0_num * xi_usq), eta_found);
    // ensure sign of y and sign of u agree
    y.conditional_negate(u.sgn0() ^ y.sgn0());

    G2Projective {
        x: x_num,
        y: y * x_den,
        z: x_den,
    }
}

/// Maps from an iso-G2 point to a G2 point.
fn iso_map(u: &G2Projective) -> G2Projective {
    const COEFFS: [&[Fp2]; 4] = [&ISO3_XNUM, &ISO3_XDEN, &ISO3_YNUM, &ISO3_YDEN];

    // unpack input point
    let G2Projective { x, y, z } = *u;

    // xnum, xden, ynum, yden
    let mut mapvals = [Fp2::zero(); 4];

    // compute powers of z
    let zsq = z.square();
    let zpows = [z, zsq, zsq * z];

    // compute map value by Horner's rule
    for idx in 0..4 {
        let coeff = COEFFS[idx];
        let clast = coeff.len() - 1;
        mapvals[idx] = coeff[clast];
        for jdx in 0..clast {
            mapvals[idx] = mapvals[idx] * x + zpows[jdx] * coeff[clast - 1 - jdx];
        }
    }

    // x denominator is order 1 less than x numerator, so we need an extra factor of z
    mapvals[1] *= z;

    // multiply result of Y map by the y-coord, y / z
    mapvals[2] *= y;
    mapvals[3] *= z;

    G2Projective {
        x: mapvals[0] * mapvals[3], // xnum * yden,
        y: mapvals[2] * mapvals[1], // ynum * xden,
        z: mapvals[1] * mapvals[3], // xden * yden
    }
}

impl MapToCurve for G2Projective {
    type Field = Fp2;

    fn map_to_curve(u: &Fp2) -> G2Projective {
        let pt = map_to_curve_simple_swu(u);
        iso_map(&pt)
    }

    fn clear_h(&self) -> Self {
        self.clear_cofactor()
    }
}

#[cfg(test)]
fn check_g2_prime(pt: &G2Projective) -> bool {
    // (X : Y : Z)==(X/Z, Y/Z) is on E': y^2 = x^3 + A * x + B.
    // y^2 z = (x^3) + A (x z^2) + B z^3
    let zsq = pt.z.square();
    (pt.y.square() * pt.z)
        == (pt.x.square() * pt.x + SSWU_ELLP_A * pt.x * zsq + SSWU_ELLP_B * zsq * pt.z)
}

#[test]
fn test_osswu_semirandom() {
    use rand_core::SeedableRng;
    let mut rng = rand_xorshift::XorShiftRng::from_seed([
        0x59, 0x62, 0xbe, 0x5d, 0x76, 0x3d, 0x31, 0x8d, 0x17, 0xdb, 0x37, 0x32, 0x54, 0x06, 0xbc,
        0xe5,
    ]);
    for _ in 0..32 {
        let input = Fp2::random(&mut rng);
        let p = map_to_curve_simple_swu(&input);
        assert!(check_g2_prime(&p));

        let p_iso = iso_map(&p);
        assert!(bool::from(p_iso.is_on_curve()));
    }
}

// test vectors from the draft 10 RFC
#[test]
fn test_encode_to_curve_10() {
    use crate::bls12_381::{
        g2::G2Affine,
        hash_to_curve::{ExpandMsgXmd, HashToCurve},
    };
    use std::string::{String, ToString};

    struct TestCase {
        msg: &'static [u8],
        expected: [&'static str; 4],
    }
    impl TestCase {
        fn expected(&self) -> String {
            self.expected[0].to_string() + self.expected[1] + self.expected[2] + self.expected[3]
        }
    }

    const DOMAIN: &[u8] = b"QUUX-V01-CS02-with-BLS12381G2_XMD:SHA-256_SSWU_NU_";

    let cases = vec![
        TestCase {
            msg: b"",
            expected: [
                "126b855e9e69b1f691f816e48ac6977664d24d99f8724868a184186469ddfd4617367e94527d4b74fc86413483afb35b",
                "00e7f4568a82b4b7dc1f14c6aaa055edf51502319c723c4dc2688c7fe5944c213f510328082396515734b6612c4e7bb7",
                "1498aadcf7ae2b345243e281ae076df6de84455d766ab6fcdaad71fab60abb2e8b980a440043cd305db09d283c895e3d",
                "0caead0fd7b6176c01436833c79d305c78be307da5f6af6c133c47311def6ff1e0babf57a0fb5539fce7ee12407b0a42",
            ],
        },
        TestCase {
            msg: b"abc",
            expected: [
                "0296238ea82c6d4adb3c838ee3cb2346049c90b96d602d7bb1b469b905c9228be25c627bffee872def773d5b2a2eb57d",
                "108ed59fd9fae381abfd1d6bce2fd2fa220990f0f837fa30e0f27914ed6e1454db0d1ee957b219f61da6ff8be0d6441f",
                "153606c417e59fb331b7ae6bce4fbf7c5190c33ce9402b5ebe2b70e44fca614f3f1382a3625ed5493843d0b0a652fc3f",
                "033f90f6057aadacae7963b0a0b379dd46750c1c94a6357c99b65f63b79e321ff50fe3053330911c56b6ceea08fee656",
            ],
        },
        TestCase {
            msg: b"abcdef0123456789",
            expected: [
                "0da75be60fb6aa0e9e3143e40c42796edf15685cafe0279afd2a67c3dff1c82341f17effd402e4f1af240ea90f4b659b",
                "038af300ef34c7759a6caaa4e69363cafeed218a1f207e93b2c70d91a1263d375d6730bd6b6509dcac3ba5b567e85bf3",
                "0492f4fed741b073e5a82580f7c663f9b79e036b70ab3e51162359cec4e77c78086fe879b65ca7a47d34374c8315ac5e",
                "19b148cbdf163cf0894f29660d2e7bfb2b68e37d54cc83fd4e6e62c020eaa48709302ef8e746736c0e19342cc1ce3df4",
            ]
        },
        TestCase {
            msg: b"q128_qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq\
                   qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq\
                   qqqqqqqqqqqqqqqqqqqqqqqqq",
            expected: [
                "12c8c05c1d5fc7bfa847f4d7d81e294e66b9a78bc9953990c358945e1f042eedafce608b67fdd3ab0cb2e6e263b9b1ad",
                "0c5ae723be00e6c3f0efe184fdc0702b64588fe77dda152ab13099a3bacd3876767fa7bbad6d6fd90b3642e902b208f9",
                "11c624c56dbe154d759d021eec60fab3d8b852395a89de497e48504366feedd4662d023af447d66926a28076813dd646",
                "04e77ddb3ede41b5ec4396b7421dd916efc68a358a0d7425bddd253547f2fb4830522358491827265dfc5bcc1928a569",
            ]
        },
        TestCase {
            msg: b"a512_aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\
                   aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\
                   aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\
                   aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\
                   aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\
                   aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\
                   aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\
                   aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\
                   aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\
                   aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
            expected: [
                "1565c2f625032d232f13121d3cfb476f45275c303a037faa255f9da62000c2c864ea881e2bcddd111edc4a3c0da3e88d",
                "0ea4e7c33d43e17cc516a72f76437c4bf81d8f4eac69ac355d3bf9b71b8138d55dc10fd458be115afa798b55dac34be1",
                "0f8991d2a1ad662e7b6f58ab787947f1fa607fce12dde171bc17903b012091b657e15333e11701edcf5b63ba2a561247",
                "043b6f5fe4e52c839148dc66f2b3751e69a0f6ebb3d056d6465d50d4108543ecd956e10fa1640dfd9bc0030cc2558d28",
            ]
        }
    ];

    for case in cases {
        let g = <G2Projective as HashToCurve<ExpandMsgXmd<sha2::Sha256>>>::encode_to_curve(
            case.msg, DOMAIN,
        );
        let g_uncompressed = G2Affine::from(g).to_uncompressed_be();

        assert_eq!(case.expected(), hex::encode(g_uncompressed.as_ref()));
    }
}

// test vectors from the draft 10 RFC
#[test]
fn test_hash_to_curve_10() {
    use crate::bls12_381::{
        g2::G2Affine,
        hash_to_curve::{ExpandMsgXmd, HashToCurve},
    };
    use std::string::{String, ToString};

    struct TestCase {
        msg: &'static [u8],
        expected: [&'static str; 4],
    }
    impl TestCase {
        fn expected(&self) -> String {
            self.expected[0].to_string() + self.expected[1] + self.expected[2] + self.expected[3]
        }
    }

    const DOMAIN: &[u8] = b"QUUX-V01-CS02-with-BLS12381G2_XMD:SHA-256_SSWU_RO_";

    let cases = vec![
        TestCase {
            msg: b"",
            expected: [
                "05cb8437535e20ecffaef7752baddf98034139c38452458baeefab379ba13dff5bf5dd71b72418717047f5b0f37da03d",
                "0141ebfbdca40eb85b87142e130ab689c673cf60f1a3e98d69335266f30d9b8d4ac44c1038e9dcdd5393faf5c41fb78a",
                "12424ac32561493f3fe3c260708a12b7c620e7be00099a974e259ddc7d1f6395c3c811cdd19f1e8dbf3e9ecfdcbab8d6",
                "0503921d7f6a12805e72940b963c0cf3471c7b2a524950ca195d11062ee75ec076daf2d4bc358c4b190c0c98064fdd92",
            ],
        },
        TestCase {
            msg: b"abc",
            expected: [
                "139cddbccdc5e91b9623efd38c49f81a6f83f175e80b06fc374de9eb4b41dfe4ca3a230ed250fbe3a2acf73a41177fd8",
                "02c2d18e033b960562aae3cab37a27ce00d80ccd5ba4b7fe0e7a210245129dbec7780ccc7954725f4168aff2787776e6",
                "00aa65dae3c8d732d10ecd2c50f8a1baf3001578f71c694e03866e9f3d49ac1e1ce70dd94a733534f106d4cec0eddd16",
                "1787327b68159716a37440985269cf584bcb1e621d3a7202be6ea05c4cfe244aeb197642555a0645fb87bf7466b2ba48",
            ],
        },
        TestCase {
            msg: b"abcdef0123456789",
            expected: [
                "190d119345b94fbd15497bcba94ecf7db2cbfd1e1fe7da034d26cbba169fb3968288b3fafb265f9ebd380512a71c3f2c",
                "121982811d2491fde9ba7ed31ef9ca474f0e1501297f68c298e9f4c0028add35aea8bb83d53c08cfc007c1e005723cd0",
                "0bb5e7572275c567462d91807de765611490205a941a5a6af3b1691bfe596c31225d3aabdf15faff860cb4ef17c7c3be",
                "05571a0f8d3c08d094576981f4a3b8eda0a8e771fcdcc8ecceaf1356a6acf17574518acb506e435b639353c2e14827c8",
            ]
        },
        TestCase {
            msg: b"q128_qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq\
                   qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq\
                   qqqqqqqqqqqqqqqqqqqqqqqqq",
            expected: [
                "0934aba516a52d8ae479939a91998299c76d39cc0c035cd18813bec433f587e2d7a4fef038260eef0cef4d02aae3eb91",
                "19a84dd7248a1066f737cc34502ee5555bd3c19f2ecdb3c7d9e24dc65d4e25e50d83f0f77105e955d78f4762d33c17da",
                "09bcccfa036b4847c9950780733633f13619994394c23ff0b32fa6b795844f4a0673e20282d07bc69641cee04f5e5662",
                "14f81cd421617428bc3b9fe25afbb751d934a00493524bc4e065635b0555084dd54679df1536101b2c979c0152d09192",
            ]
        },
        TestCase {
            msg: b"a512_aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\
                   aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\
                   aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\
                   aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\
                   aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\
                   aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\
                   aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\
                   aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\
                   aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\
                   aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
            expected: [
                "11fca2ff525572795a801eed17eb12785887c7b63fb77a42be46ce4a34131d71f7a73e95fee3f812aea3de78b4d01569",
                "01a6ba2f9a11fa5598b2d8ace0fbe0a0eacb65deceb476fbbcb64fd24557c2f4b18ecfc5663e54ae16a84f5ab7f62534",
                "03a47f8e6d1763ba0cad63d6114c0accbef65707825a511b251a660a9b3994249ae4e63fac38b23da0c398689ee2ab52",
                "0b6798718c8aed24bc19cb27f866f1c9effcdbf92397ad6448b5c9db90d2b9da6cbabf48adc1adf59a1a28344e79d57e",
            ]
        }
    ];

    for case in cases {
        let g = <G2Projective as HashToCurve<ExpandMsgXmd<sha2::Sha256>>>::hash_to_curve(
            case.msg, DOMAIN,
        );
        let g_uncompressed = G2Affine::from(g).to_uncompressed_be();

        assert_eq!(case.expected(), hex::encode(g_uncompressed.as_ref()));
    }
}

#[test]
fn test_sgn0() {
    use super::map_g1::P_M1_OVER2;

    assert!(!bool::from(Fp2::zero().sgn0()));
    assert!(bool::from(Fp2::one().sgn0()));
    assert!(bool::from(
        Fp2 {
            c0: P_M1_OVER2,
            c1: Fp::zero()
        }
        .sgn0()
    ));
    assert!(bool::from(
        Fp2 {
            c0: P_M1_OVER2,
            c1: Fp::one()
        }
        .sgn0()
    ));
    assert!(bool::from(
        Fp2 {
            c0: Fp::zero(),
            c1: P_M1_OVER2,
        }
        .sgn0()
    ));
    assert!(bool::from(
        Fp2 {
            c0: Fp::one(),
            c1: P_M1_OVER2,
        }
        .sgn0()
    ));

    let p_p1_over2 = P_M1_OVER2 + Fp::one();
    assert!(!bool::from(
        Fp2 {
            c0: p_p1_over2,
            c1: Fp::zero()
        }
        .sgn0()
    ));
    assert!(!bool::from(
        Fp2 {
            c0: p_p1_over2,
            c1: Fp::one()
        }
        .sgn0()
    ));
    assert!(!bool::from(
        Fp2 {
            c0: Fp::zero(),
            c1: p_p1_over2,
        }
        .sgn0()
    ));
    assert!(bool::from(
        Fp2 {
            c0: Fp::one(),
            c1: p_p1_over2,
        }
        .sgn0()
    ));

    assert!(bool::from(
        Fp2 {
            c0: P_M1_OVER2,
            c1: -Fp::one()
        }
        .sgn0()
    ));
    assert!(!bool::from(
        Fp2 {
            c0: p_p1_over2,
            c1: -Fp::one()
        }
        .sgn0()
    ));
    assert!(!bool::from(
        Fp2 {
            c0: Fp::zero(),
            c1: -Fp::one()
        }
        .sgn0()
    ));
    assert!(bool::from(
        Fp2 {
            c0: P_M1_OVER2,
            c1: p_p1_over2
        }
        .sgn0()
    ));
    assert!(!bool::from(
        Fp2 {
            c0: p_p1_over2,
            c1: P_M1_OVER2
        }
        .sgn0()
    ));

    assert!(!bool::from(
        Fp2 {
            c0: -Fp::one(),
            c1: P_M1_OVER2,
        }
        .sgn0()
    ));
    assert!(!bool::from(
        Fp2 {
            c0: -Fp::one(),
            c1: p_p1_over2,
        }
        .sgn0()
    ));
    assert!(!bool::from(
        Fp2 {
            c0: -Fp::one(),
            c1: Fp::zero(),
        }
        .sgn0()
    ));
    assert!(!bool::from(
        Fp2 {
            c0: p_p1_over2,
            c1: P_M1_OVER2,
        }
        .sgn0()
    ));
    assert!(bool::from(
        Fp2 {
            c0: P_M1_OVER2,
            c1: p_p1_over2,
        }
        .sgn0()
    ));
}
halo2curves_axiom/bls12_381/hash_to_curve/map_g2.rs

halo2curves_axiom/bls12_381/hash_to_curve/
map_g2.rs
