primitives/sharing/authenticated/batched/

field_keys.rs

use std::{
    fmt::Debug,
    iter::Sum as IterSum,
    ops::{Add, AddAssign, Mul, MulAssign, Neg, Sub, SubAssign},
};

use serde::{Deserialize, Serialize};
use subtle::{Choice, ConstantTimeEq};
use typenum::{Prod, Sum, U1, U2, U3};

use crate::{
    algebra::field::{FieldElement, FieldExtension, SubfieldElement},
    errors::PrimitiveError,
    izip_eq,
    random::{CryptoRngCore, Random, RandomWith},
    sharing::{FieldShareKey, GlobalFieldKey, OpenFieldShares},
    types::{
        heap_array::{FieldElements, SubfieldElements},
        ConditionallySelectable,
        HeapArray,
        Positive,
    },
};

// α and β, such that MAC(x) = α · x + β
// In the context of VOLE, this corresponds to w = Δ · u + v
#[derive(Clone, Default, PartialEq, Eq, Serialize, Deserialize)]
#[serde(bound = "F: FieldExtension, M: Positive")]
pub struct FieldShareKeys<F, M>
where
    F: FieldExtension,
    M: Positive, // M is the number of shares
{
    pub(crate) alpha: GlobalFieldKey<F>,   // α, global key
    pub(crate) betas: FieldElements<F, M>, // β, a local key per shared value.
}

impl<F: FieldExtension, M: Positive> FieldShareKeys<F, M> {
    #[inline]
    pub fn new(alpha: GlobalFieldKey<F>, betas: FieldElements<F, M>) -> Self {
        FieldShareKeys { alpha, betas }
    }

    #[inline]
    pub fn get_alpha(&self) -> GlobalFieldKey<F> {
        self.alpha.clone()
    }

    #[inline]
    pub fn get_alpha_value(&self) -> FieldElement<F> {
        *self.alpha
    }

    #[inline]
    pub fn get_betas(&self) -> &FieldElements<F, M> {
        &self.betas
    }

    /* === Verification === */

    #[inline]
    pub fn compute_mac(&self, values: &SubfieldElements<F, M>) -> FieldElements<F, M> {
        izip_eq!(&self.betas, values)
            .map(|(beta, value)| (*self.alpha * value) + beta)
            .collect()
    }

    #[inline]
    pub fn verify_mac(&self, open_share: &OpenFieldShares<F, M>) -> Result<(), PrimitiveError> {
        let computed_macs = self.compute_mac(&open_share.value);
        bool::from(computed_macs.ct_eq(&open_share.mac))
            .then_some(())
            .ok_or_else(|| {
                PrimitiveError::WrongMAC(
                    serde_json::to_string(&computed_macs).unwrap(),
                    serde_json::to_string(&open_share.mac).unwrap(),
                )
            })
    }
}

impl<T: FieldExtension, M: Positive> Debug for FieldShareKeys<T, M> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct(format!("FieldShareKeys<{}>", M::SIZE).as_str())
            .field("alpha", &self.alpha)
            .field("betas", &self.betas)
            .finish()
    }
}

// --------------
// | Arithmetic |
// --------------

// === Addition === //

impl<F: FieldExtension, M: Positive> Add for FieldShareKeys<F, M> {
    type Output = FieldShareKeys<F, M>;

    #[inline]
    fn add(self, other: FieldShareKeys<F, M>) -> Self::Output {
        assert_eq!(self.alpha, other.alpha);
        FieldShareKeys {
            alpha: self.alpha,
            betas: self.betas + other.betas,
        }
    }
}

impl<F: FieldExtension, M: Positive> Add<&FieldShareKeys<F, M>> for FieldShareKeys<F, M> {
    type Output = FieldShareKeys<F, M>;

    #[inline]
    fn add(self, other: &FieldShareKeys<F, M>) -> Self::Output {
        assert_eq!(self.alpha, other.alpha);
        FieldShareKeys {
            alpha: self.alpha,
            betas: self.betas + &other.betas,
        }
    }
}

impl<F: FieldExtension, M: Positive> Add<FieldShareKeys<F, M>> for &FieldShareKeys<F, M> {
    type Output = FieldShareKeys<F, M>;

    #[inline]
    fn add(self, other: FieldShareKeys<F, M>) -> Self::Output {
        assert_eq!(self.alpha, other.alpha);
        FieldShareKeys {
            alpha: other.alpha,
            betas: other.betas + &self.betas,
        }
    }
}

// === AddAssign === //

impl<F: FieldExtension, M: Positive> AddAssign for FieldShareKeys<F, M> {
    #[inline]
    fn add_assign(&mut self, other: Self) {
        assert_eq!(self.alpha, other.alpha);
        self.betas += other.betas;
    }
}

impl<'a, F: FieldExtension, M: Positive> AddAssign<&'a FieldShareKeys<F, M>>
    for FieldShareKeys<F, M>
{
    #[inline]
    fn add_assign(&mut self, other: &'a FieldShareKeys<F, M>) {
        assert_eq!(self.alpha, other.alpha);
        self.betas += &other.betas;
    }
}

// === Subtraction === //

impl<F: FieldExtension, M: Positive> Sub for FieldShareKeys<F, M> {
    type Output = FieldShareKeys<F, M>;

    #[inline]
    fn sub(self, other: FieldShareKeys<F, M>) -> Self::Output {
        assert_eq!(self.alpha, other.alpha);
        FieldShareKeys {
            alpha: self.alpha,
            betas: self.betas - other.betas,
        }
    }
}

impl<F: FieldExtension, M: Positive> Sub<&FieldShareKeys<F, M>> for FieldShareKeys<F, M> {
    type Output = FieldShareKeys<F, M>;

    #[inline]
    fn sub(self, other: &FieldShareKeys<F, M>) -> Self::Output {
        assert_eq!(self.alpha, other.alpha);
        FieldShareKeys {
            alpha: self.alpha,
            betas: self.betas - &other.betas,
        }
    }
}

impl<F: FieldExtension, M: Positive> Sub<FieldShareKeys<F, M>> for &FieldShareKeys<F, M> {
    type Output = FieldShareKeys<F, M>;

    #[inline]
    fn sub(self, other: FieldShareKeys<F, M>) -> Self::Output {
        assert_eq!(self.alpha, other.alpha);
        FieldShareKeys {
            alpha: other.alpha,
            betas: &self.betas - other.betas,
        }
    }
}

impl<F: FieldExtension, M: Positive> Sub<&FieldShareKeys<F, M>> for &FieldShareKeys<F, M> {
    type Output = FieldShareKeys<F, M>;

    #[inline]
    fn sub(self, other: &FieldShareKeys<F, M>) -> Self::Output {
        assert_eq!(self.alpha, other.alpha);
        FieldShareKeys {
            alpha: self.alpha.clone(),
            betas: &self.betas - &other.betas,
        }
    }
}

// === SubAssign === //

impl<F: FieldExtension, M: Positive> SubAssign for FieldShareKeys<F, M> {
    #[inline]
    fn sub_assign(&mut self, other: Self) {
        assert_eq!(self.alpha, other.alpha);
        self.betas -= other.betas;
    }
}

impl<'a, F: FieldExtension, M: Positive> SubAssign<&'a FieldShareKeys<F, M>>
    for FieldShareKeys<F, M>
{
    #[inline]
    fn sub_assign(&mut self, other: &'a FieldShareKeys<F, M>) {
        assert_eq!(self.alpha, other.alpha);
        self.betas -= &other.betas;
    }
}

// === FieldElements/SubfieldElements multiplication === //

impl<F: FieldExtension, M: Positive> Mul<FieldElements<F, M>> for FieldShareKeys<F, M> {
    type Output = FieldShareKeys<F, M>;

    #[inline]
    fn mul(mut self, other: FieldElements<F, M>) -> Self::Output {
        izip_eq!(&mut self.betas, other).for_each(|(beta, value)| *beta *= value);
        self
    }
}

impl<'a, F: FieldExtension, M: Positive> Mul<&'a FieldElements<F, M>> for FieldShareKeys<F, M> {
    type Output = FieldShareKeys<F, M>;

    #[inline]
    fn mul(mut self, other: &'a FieldElements<F, M>) -> Self::Output {
        izip_eq!(&mut self.betas, other).for_each(|(beta, value)| *beta *= value);
        self
    }
}

impl<F: FieldExtension, M: Positive> Mul<SubfieldElements<F, M>> for FieldShareKeys<F, M> {
    type Output = FieldShareKeys<F, M>;

    #[inline]
    fn mul(mut self, other: SubfieldElements<F, M>) -> Self::Output {
        izip_eq!(&mut self.betas, other).for_each(|(beta, value)| *beta *= value);
        self
    }
}

impl<'a, F: FieldExtension, M: Positive> Mul<&'a SubfieldElements<F, M>> for FieldShareKeys<F, M> {
    type Output = FieldShareKeys<F, M>;

    #[inline]
    fn mul(mut self, other: &'a SubfieldElements<F, M>) -> Self::Output {
        izip_eq!(&mut self.betas, other).for_each(|(beta, value)| *beta *= value);
        self
    }
}

// === One-to-many FieldElement/SubfieldElement multiplication === //

impl<F: FieldExtension, M: Positive> Mul<FieldElement<F>> for FieldShareKeys<F, M> {
    type Output = FieldShareKeys<F, M>;

    #[inline]
    fn mul(self, other: FieldElement<F>) -> Self::Output {
        FieldShareKeys {
            betas: self.betas * other,
            ..self
        }
    }
}

impl<'a, F: FieldExtension, M: Positive> Mul<&'a FieldElement<F>> for FieldShareKeys<F, M> {
    type Output = FieldShareKeys<F, M>;

    #[inline]
    fn mul(self, other: &'a FieldElement<F>) -> Self::Output {
        FieldShareKeys {
            betas: self.betas * other,
            ..self
        }
    }
}

impl<F: FieldExtension, M: Positive> Mul<SubfieldElement<F>> for FieldShareKeys<F, M> {
    type Output = FieldShareKeys<F, M>;

    #[inline]
    fn mul(self, other: SubfieldElement<F>) -> Self::Output {
        FieldShareKeys {
            betas: self.betas * other,
            ..self
        }
    }
}

impl<'a, F: FieldExtension, M: Positive> Mul<&'a SubfieldElement<F>> for FieldShareKeys<F, M> {
    type Output = FieldShareKeys<F, M>;

    #[inline]
    fn mul(self, other: &'a SubfieldElement<F>) -> Self::Output {
        FieldShareKeys {
            betas: self.betas * other,
            ..self
        }
    }
}

// === MulAssign === //

impl<F: FieldExtension, M: Positive> MulAssign for FieldShareKeys<F, M> {
    #[inline]
    fn mul_assign(&mut self, other: Self) {
        self.betas *= other.betas;
    }
}

impl<F: FieldExtension, M: Positive> MulAssign<FieldElement<F>> for FieldShareKeys<F, M> {
    #[inline]
    fn mul_assign(&mut self, other: FieldElement<F>) {
        izip_eq!(&mut self.betas).for_each(|beta| *beta *= other)
    }
}

impl<'a, F: FieldExtension, M: Positive> MulAssign<&'a FieldElement<F>> for FieldShareKeys<F, M> {
    #[inline]
    fn mul_assign(&mut self, other: &'a FieldElement<F>) {
        izip_eq!(&mut self.betas).for_each(|beta| *beta *= other)
    }
}

impl<F: FieldExtension, M: Positive> MulAssign<SubfieldElement<F>> for FieldShareKeys<F, M> {
    #[inline]
    fn mul_assign(&mut self, other: SubfieldElement<F>) {
        izip_eq!(&mut self.betas).for_each(|beta| *beta *= other)
    }
}

impl<'a, F: FieldExtension, M: Positive> MulAssign<&'a SubfieldElement<F>>
    for FieldShareKeys<F, M>
{
    #[inline]
    fn mul_assign(&mut self, other: &'a SubfieldElement<F>) {
        izip_eq!(&mut self.betas).for_each(|beta| *beta *= other)
    }
}

// === MulAssign with vectors === //

impl<'a, F: FieldExtension, M: Positive> MulAssign<&'a SubfieldElements<F, M>>
    for FieldShareKeys<F, M>
{
    #[inline]
    fn mul_assign(&mut self, other: &'a SubfieldElements<F, M>) {
        izip_eq!(&mut self.betas, other).for_each(|(beta, other)| *beta *= other);
    }
}

// === Negation === //

impl<F: FieldExtension, M: Positive> Neg for FieldShareKeys<F, M> {
    type Output = FieldShareKeys<F, M>;

    #[inline]
    fn neg(self) -> Self::Output {
        FieldShareKeys {
            alpha: self.alpha,
            betas: -self.betas,
        }
    }
}

impl<F: FieldExtension, M: Positive> Neg for &FieldShareKeys<F, M> {
    type Output = FieldShareKeys<F, M>;

    #[inline]
    fn neg(self) -> Self::Output {
        FieldShareKeys {
            alpha: self.alpha.clone(),
            betas: -self.betas.clone(),
        }
    }
}

// === Sum === //
impl<F: FieldExtension, M: Positive> IterSum for FieldShareKeys<F, M> {
    fn sum<I: Iterator<Item = Self>>(mut iter: I) -> Self {
        let first = iter.next().unwrap_or_default();
        iter.fold(first, |acc, x| acc + x)
    }
}

// === Constant addition / subtraction === //

impl<F: FieldExtension, M: Positive> FieldShareKeys<F, M> {
    #[inline]
    pub fn add_secret_owned(mut self, constant: SubfieldElement<F>) -> Self {
        self.betas -= *self.alpha * constant;
        self
    }

    #[inline]
    pub fn add_secret(&self, constant: SubfieldElement<F>) -> Self {
        let mut result = self.clone();
        result.betas -= *result.alpha * constant;
        result
    }

    #[inline]
    pub fn add_constant_array(&self, constant: SubfieldElements<F, M>) -> Self {
        let mut result = self.clone();
        result.betas -= constant
            .iter()
            .map(|c| *result.alpha * c)
            .collect::<FieldElements<F, M>>();
        result
    }

    #[inline]
    pub fn add_constant_array_owned(&mut self, constant: &SubfieldElements<F, M>) {
        izip_eq!(&mut self.betas, constant).for_each(|(beta, c)| *beta -= *self.alpha * c);
    }
}

// -------------------------
// |   Random Generation   |
// -------------------------

impl<F: FieldExtension, M: Positive> Random for FieldShareKeys<F, M> {
    fn random(mut rng: impl CryptoRngCore) -> Self {
        FieldShareKeys {
            alpha: GlobalFieldKey::random(&mut rng),
            betas: FieldElements::random(&mut rng),
        }
    }
}

impl<F: FieldExtension, M: Positive> RandomWith<GlobalFieldKey<F>> for FieldShareKeys<F, M> {
    /// Generates a random set of field share keys with the given global key `alpha`.
    fn random_with(mut rng: impl CryptoRngCore, alpha: GlobalFieldKey<F>) -> Self {
        FieldShareKeys {
            alpha,
            betas: FieldElements::random(&mut rng),
        }
    }
}

// -----------------------
// |   Split and Merge   |
// -----------------------

impl<F: FieldExtension, M: Positive> FieldShareKeys<F, M> {
    // Split into two keys with batch sizes M1 and M2
    pub fn split<M1, M2>(self) -> (FieldShareKeys<F, M1>, FieldShareKeys<F, M2>)
    where
        M1: Positive,
        M2: Positive + Add<M1, Output = M>,
    {
        let FieldShareKeys { alpha, betas } = self;

        let (betas1, betas2) = betas.split::<M1, M2>();
        (
            FieldShareKeys::new(alpha.clone(), betas1),
            FieldShareKeys::new(alpha, betas2),
        )
    }

    // Split batch of M keys into two key batches of equal size (M/2)
    pub fn split_halves<MDiv2>(self) -> (FieldShareKeys<F, MDiv2>, FieldShareKeys<F, MDiv2>)
    where
        MDiv2: Positive + Mul<U2, Output = M>,
    {
        let FieldShareKeys { alpha, betas } = self;

        let (betas1, betas2) = betas.split_halves::<MDiv2>();
        (
            FieldShareKeys::new(alpha.clone(), betas1),
            FieldShareKeys::new(alpha, betas2),
        )
    }

    // Merge two sets of keys with M keys each into a single set of keys with 2M keys.
    pub fn merge_halves(this: Self, other: Self) -> FieldShareKeys<F, Prod<M, U2>>
    where
        M: Positive + Mul<U2, Output: Positive>,
    {
        assert_eq!(this.alpha, other.alpha);
        FieldShareKeys {
            alpha: this.alpha,
            betas: FieldElements::merge_halves(this.betas, other.betas),
        }
    }

    // Split into three keys with batch sizes M1, M2, and M3
    pub fn split3<M1, M2, M3>(
        self,
    ) -> (
        FieldShareKeys<F, M1>,
        FieldShareKeys<F, M2>,
        FieldShareKeys<F, M3>,
    )
    where
        M1: Positive,
        M2: Positive + Add<M1>,
        M3: Positive + Add<Sum<M2, M1>, Output = M>,
    {
        let FieldShareKeys { alpha, betas } = self;

        let (betas1, betas2, betas3) = betas.split3::<M1, M2, M3>();
        (
            FieldShareKeys::new(alpha.clone(), betas1),
            FieldShareKeys::new(alpha.clone(), betas2),
            FieldShareKeys::new(alpha, betas3),
        )
    }

    // Split into three keys with batches of equal size (M/3)
    pub fn split_thirds<MDiv3>(
        self,
    ) -> (
        FieldShareKeys<F, MDiv3>,
        FieldShareKeys<F, MDiv3>,
        FieldShareKeys<F, MDiv3>,
    )
    where
        MDiv3: Positive + Mul<U3, Output = M>,
    {
        let FieldShareKeys { alpha, betas } = self;

        let (betas1, betas2, betas3) = betas.split_thirds::<MDiv3>();
        (
            FieldShareKeys::new(alpha.clone(), betas1),
            FieldShareKeys::new(alpha.clone(), betas2),
            FieldShareKeys::new(alpha, betas3),
        )
    }

    // Merge three sets of keys with M keys each into a single set of keys with 3M keys.
    pub fn merge_thirds(first: Self, second: Self, third: Self) -> FieldShareKeys<F, Prod<M, U3>>
    where
        M: Positive + Mul<U3, Output: Positive>,
    {
        assert_eq!(first.alpha, second.alpha);
        assert_eq!(first.alpha, third.alpha);
        FieldShareKeys {
            alpha: first.alpha,
            betas: FieldElements::merge_thirds(first.betas, second.betas, third.betas),
        }
    }
}

// === Constant time equality / selection === //

impl<F: FieldExtension, M: Positive> ConstantTimeEq for FieldShareKeys<F, M> {
    #[inline]
    fn ct_eq(&self, other: &Self) -> Choice {
        self.alpha.ct_eq(&other.alpha) & self.betas.ct_eq(&other.betas)
    }
}

impl<F: FieldExtension, M: Positive> ConditionallySelectable for FieldShareKeys<F, M> {
    #[inline]
    fn conditional_select(a: &Self, b: &Self, choice: Choice) -> Self {
        FieldShareKeys {
            alpha: GlobalFieldKey::conditional_select(&a.alpha, &b.alpha, choice),
            betas: HeapArray::conditional_select(&a.betas, &b.betas, choice),
        }
    }
}

// ------------------------
// |   Iterate and Cast   |
// ------------------------

// === Single key === //

impl<F: FieldExtension> From<FieldShareKey<F>> for FieldShareKeys<F, U1> {
    fn from(key: FieldShareKey<F>) -> Self {
        FieldShareKeys {
            alpha: key.alpha,
            betas: HeapArray::from(key.beta),
        }
    }
}

// === Iterators === //

pub struct FieldShareKeysIterator<F, M>
where
    F: FieldExtension,
    M: Positive,
{
    keys: FieldShareKeys<F, M>,
    index: usize,
}

impl<F: FieldExtension, M: Positive> Iterator for FieldShareKeysIterator<F, M> {
    type Item = FieldShareKey<F>;

    fn next(&mut self) -> Option<Self::Item> {
        if self.index < M::to_usize() {
            let key = FieldShareKey {
                alpha: self.keys.alpha.clone(),
                beta: self.keys.betas[self.index],
            };
            self.index += 1;
            Some(key)
        } else {
            None
        }
    }
}

impl<F: FieldExtension, M: Positive> ExactSizeIterator for FieldShareKeysIterator<F, M> {
    fn len(&self) -> usize {
        M::to_usize()
    }
}

impl<F: FieldExtension, M: Positive> IntoIterator for FieldShareKeys<F, M> {
    type Item = FieldShareKey<F>;
    type IntoIter = FieldShareKeysIterator<F, M>;

    fn into_iter(self) -> Self::IntoIter {
        FieldShareKeysIterator::<F, M> {
            keys: self,
            index: 0,
        }
    }
}

pub struct FieldShareKeyRef<'a, F>
where
    F: FieldExtension,
{
    pub alpha: GlobalFieldKey<F>,
    pub beta: &'a FieldElement<F>,
}

impl<'a, F> From<FieldShareKeyRef<'a, F>> for FieldShareKey<F>
where
    F: FieldExtension,
{
    fn from(val: FieldShareKeyRef<'a, F>) -> Self {
        FieldShareKey {
            alpha: val.alpha,
            beta: *val.beta,
        }
    }
}

pub struct FieldShareKeysRefIterator<'a, F, M>
where
    F: FieldExtension,
    M: Positive,
{
    keys: &'a FieldShareKeys<F, M>,
    index: usize,
}

impl<F: FieldExtension, M: Positive> ExactSizeIterator for FieldShareKeysRefIterator<'_, F, M> {
    fn len(&self) -> usize {
        M::to_usize()
    }
}

impl<'a, F: FieldExtension, M: Positive> Iterator for FieldShareKeysRefIterator<'a, F, M> {
    type Item = FieldShareKeyRef<'a, F>;

    fn next(&mut self) -> Option<Self::Item> {
        if self.index < M::to_usize() {
            let key = FieldShareKeyRef {
                alpha: self.keys.alpha.clone(),
                beta: &self.keys.betas[self.index],
            };
            self.index += 1;
            Some(key)
        } else {
            None
        }
    }
}

impl<'a, F: FieldExtension, M: Positive> IntoIterator for &'a FieldShareKeys<F, M> {
    type Item = FieldShareKeyRef<'a, F>;
    type IntoIter = FieldShareKeysRefIterator<'a, F, M>;

    fn into_iter(self) -> Self::IntoIter {
        FieldShareKeysRefIterator {
            keys: self,
            index: 0,
        }
    }
}

#[cfg(test)]
mod tests {
    use typenum::U10;

    use super::*;
    use crate::algebra::elliptic_curve::{Curve25519Ristretto as C, ScalarAsExtension};

    pub type FrExt = ScalarAsExtension<C>;

    #[test]
    fn test_addition() {
        let alpha = GlobalFieldKey::new(FrExt::from(3u32));
        let key1 = FieldShareKeys {
            alpha: alpha.clone(),
            betas: HeapArray::<_, U10>::from_fn(|_| FrExt::from(10u32)),
        };
        let key2 = FieldShareKeys {
            alpha: alpha.clone(),
            betas: HeapArray::<_, U10>::from_fn(|_| FrExt::from(7u32)),
        };
        let expected_result = FieldShareKeys {
            alpha,
            betas: HeapArray::<_, U10>::from_fn(|_| FrExt::from(17u32)),
        };
        assert_eq!(key1 + key2, expected_result);
    }

    #[test]
    fn test_subtraction() {
        let alpha = GlobalFieldKey::new(FrExt::from(3u32));
        let key1 = FieldShareKeys {
            alpha: alpha.clone(),
            betas: HeapArray::<_, U10>::from_fn(|_| FrExt::from(10u32)),
        };
        let key2 = FieldShareKeys {
            alpha: alpha.clone(),
            betas: HeapArray::<_, U10>::from_fn(|_| FrExt::from(7u32)),
        };
        let expected_result = FieldShareKeys {
            alpha,
            betas: HeapArray::<_, U10>::from_fn(|_| FrExt::from(3u32)),
        };
        assert_eq!(key1 - key2, expected_result);
    }

    #[test]
    fn test_multiplication() {
        let alpha = GlobalFieldKey::new(FrExt::from(3u32));
        let key = FieldShareKeys {
            alpha: alpha.clone(),
            betas: HeapArray::<_, U10>::from_fn(|_| FrExt::from(10u32)),
        };
        let scalar = FrExt::from(3u32);
        let expected_result = FieldShareKeys {
            alpha,
            betas: HeapArray::<_, U10>::from_fn(|_| FrExt::from(30u32)),
        };
        assert_eq!(key * scalar, expected_result);
    }

    #[test]
    fn test_negation() {
        let key = FieldShareKeys {
            alpha: GlobalFieldKey::new(FrExt::from(5u32)),
            betas: HeapArray::<_, U10>::from_fn(|_| FrExt::from(10u32)),
        };
        let expected_result = FieldShareKeys {
            alpha: GlobalFieldKey::new(FrExt::from(5u32)),
            betas: -HeapArray::<_, U10>::from_fn(|_| FrExt::from(10u32)),
        };
        assert_eq!(-key, expected_result);
    }
}