Function reshare

ciphercore-base/src/mpc/resharing.rs:246–269

Convert 3-out-of-3 to 2-out-of-3 shares

(input_shares: &Node, prf_keys: &Node)

// Convert 3-out-of-3 to 2-out-of-3 shares
pub(super) fn reshare(input_shares: &Node, prf_keys: &Node) -> Result<Node> {
    let g = input_shares.get_graph();

    let input_shares_vec: Vec<Node> = (0..PARTIES)
        .map(|i| input_shares.tuple_get(i as u64).unwrap())
        .collect();
    let zero_shares =
        get_zero_shares(g.clone(), prf_keys.clone(), input_shares_vec[0].get_type()?)?;

    let mut output_shares_vec = vec![];
    for i in 0..PARTIES {
        // Party i masks its 3-out-of-3 share: input_i + zero_share_i
        let masked_share = recursively_sum_shares(
            g.clone(),
            vec![input_shares_vec[i].clone(), zero_shares[i].clone()],
        )?;
        // Party i sends output share to party (i-1)
        let sent_share = g.nop(masked_share)?;
        let im1 = ((i + PARTIES - 1) % PARTIES) as u64;
        sent_share.add_annotation(NodeAnnotation::Send(i as u64, im1))?;
        output_shares_vec.push(sent_share);
    }
    g.create_tuple(output_shares_vec)
}

#[cfg(test)]
mod tests {