Function share_vector

ciphercore-base/src/mpc/utils.rs:150–204

Utility function for preparing secret-shared data. TODO: in the future, we need to make secret-sharing more generic. # Arguments `prng` - PRNG object (for randomness). `data` - array to secret-share. `scalar_type` - scalar type to use. # Returns Vector of shares.

(
    prng: &mut PRNG,
    data: &[T],
    scalar_type: ScalarType,
)

///
/// Vector of shares.
pub fn share_vector<T: TryInto<u128> + Not<Output = T> + TryInto<u8> + Copy>(
    prng: &mut PRNG,
    data: &[T],
    scalar_type: ScalarType,
) -> Result<Vec<Value>> {
    let n = data.len();
    let n_bytes = n * scalar_size_in_bytes(scalar_type) as usize;

    // first share (r0) is pseudo-random
    let r0_bytes = prng.get_random_bytes(n_bytes)?;
    let r0 = Value::from_bytes(r0_bytes)
        .to_flattened_array_u128(array_type(vec![n as u64], scalar_type))?;
    // second share (r1) is pseudo-random
    let r1_bytes = prng.get_random_bytes(n_bytes)?;
    let r1 = Value::from_bytes(r1_bytes)
        .to_flattened_array_u128(array_type(vec![n as u64], scalar_type))?;
    // third share (r2) is r2 = data - (r0 + r1)
    let r0r1 = add_vectors_u128(&r0, &r1, scalar_type.get_modulus())?;
    let data_u128 = Value::from_flattened_array(data, scalar_type)?
        .to_flattened_array_u128(array_type(vec![n as u64], scalar_type))?;
    let r2 = subtract_vectors_u128(&data_u128, &r0r1, scalar_type.get_modulus())?;

    let shares = vec![
        Value::from_flattened_array(&r0, scalar_type)?,
        Value::from_flattened_array(&r1, scalar_type)?,
        Value::from_flattened_array(&r2, scalar_type)?,
    ];

    let mut garbage = vec![];
    for _ in 0..3 {
        garbage.push(Value::from_flattened_array(
            &prng.get_random_bytes(n_bytes)?,
            UINT8,
        )?);
    }

    // convert the shares to a value
    Ok(vec![
        Value::from_vector(vec![
            shares[0].clone(),
            shares[1].clone(),
            garbage[2].clone(),
        ]),
        Value::from_vector(vec![
            garbage[0].clone(),
            shares[1].clone(),
            shares[2].clone(),
        ]),
        Value::from_vector(vec![
            shares[0].clone(),
            garbage[1].clone(),
            shares[2].clone(),
        ]),
    ])
}

/// Selects elements of node 0 if bits of node b are zero and elements of node 1 otherwise.
///