miracl_core_bls12381 4.2.2

/*
 * Copyright (c) 2012-2020 MIRACL UK Ltd.
 *
 * This file is part of MIRACL Core
 * (see https://github.com/miracl/core).
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/* Shamir threshold secret sharing module */
/* Split any byte array into number of shares < 256 */
/* Specify number of shares required for recovery - nsr */

/* See TestMPIN.rs for an example of use */

use crate::rand::RAND;

const PTAB: [u8; 256] = [
    1, 3, 5, 15, 17, 51, 85, 255, 26, 46, 114, 150, 161, 248, 19, 53, 95, 225, 56, 72, 216, 115,
    149, 164, 247, 2, 6, 10, 30, 34, 102, 170, 229, 52, 92, 228, 55, 89, 235, 38, 106, 190, 217,
    112, 144, 171, 230, 49, 83, 245, 4, 12, 20, 60, 68, 204, 79, 209, 104, 184, 211, 110, 178, 205,
    76, 212, 103, 169, 224, 59, 77, 215, 98, 166, 241, 8, 24, 40, 120, 136, 131, 158, 185, 208,
    107, 189, 220, 127, 129, 152, 179, 206, 73, 219, 118, 154, 181, 196, 87, 249, 16, 48, 80, 240,
    11, 29, 39, 105, 187, 214, 97, 163, 254, 25, 43, 125, 135, 146, 173, 236, 47, 113, 147, 174,
    233, 32, 96, 160, 251, 22, 58, 78, 210, 109, 183, 194, 93, 231, 50, 86, 250, 21, 63, 65, 195,
    94, 226, 61, 71, 201, 64, 192, 91, 237, 44, 116, 156, 191, 218, 117, 159, 186, 213, 100, 172,
    239, 42, 126, 130, 157, 188, 223, 122, 142, 137, 128, 155, 182, 193, 88, 232, 35, 101, 175,
    234, 37, 111, 177, 200, 67, 197, 84, 252, 31, 33, 99, 165, 244, 7, 9, 27, 45, 119, 153, 176,
    203, 70, 202, 69, 207, 74, 222, 121, 139, 134, 145, 168, 227, 62, 66, 198, 81, 243, 14, 18, 54,
    90, 238, 41, 123, 141, 140, 143, 138, 133, 148, 167, 242, 13, 23, 57, 75, 221, 124, 132, 151,
    162, 253, 28, 36, 108, 180, 199, 82, 246, 1,
];

const LTAB: [u8; 256] = [
    0, 255, 25, 1, 50, 2, 26, 198, 75, 199, 27, 104, 51, 238, 223, 3, 100, 4, 224, 14, 52, 141,
    129, 239, 76, 113, 8, 200, 248, 105, 28, 193, 125, 194, 29, 181, 249, 185, 39, 106, 77, 228,
    166, 114, 154, 201, 9, 120, 101, 47, 138, 5, 33, 15, 225, 36, 18, 240, 130, 69, 53, 147, 218,
    142, 150, 143, 219, 189, 54, 208, 206, 148, 19, 92, 210, 241, 64, 70, 131, 56, 102, 221, 253,
    48, 191, 6, 139, 98, 179, 37, 226, 152, 34, 136, 145, 16, 126, 110, 72, 195, 163, 182, 30, 66,
    58, 107, 40, 84, 250, 133, 61, 186, 43, 121, 10, 21, 155, 159, 94, 202, 78, 212, 172, 229, 243,
    115, 167, 87, 175, 88, 168, 80, 244, 234, 214, 116, 79, 174, 233, 213, 231, 230, 173, 232, 44,
    215, 117, 122, 235, 22, 11, 245, 89, 203, 95, 176, 156, 169, 81, 160, 127, 12, 246, 111, 23,
    196, 73, 236, 216, 67, 31, 45, 164, 118, 123, 183, 204, 187, 62, 90, 251, 96, 177, 134, 59, 82,
    161, 108, 170, 85, 41, 157, 151, 178, 135, 144, 97, 190, 220, 252, 188, 149, 207, 205, 55, 63,
    91, 209, 83, 57, 132, 60, 65, 162, 109, 71, 20, 42, 158, 93, 86, 242, 211, 171, 68, 17, 146,
    217, 35, 32, 46, 137, 180, 124, 184, 38, 119, 153, 227, 165, 103, 74, 237, 222, 197, 49, 254,
    24, 13, 99, 140, 128, 192, 247, 112, 7,
];

pub struct SHARE<'a> {
    id: u8,
    nsr: u8,
    b: &'a [u8]
}

fn mul(x: u8, y: u8) -> u8 {
/* x.y= AntiLog(Log(x) + Log(y)) */
    let ix = (x as usize) & 0xff;
    let iy = (y as usize) & 0xff;
    let lx = (LTAB[ix] as usize) & 0xff;
    let ly = (LTAB[iy] as usize) & 0xff;

    if x != 0 && y != 0 {
        PTAB[(lx + ly) % 255]
    } else {
        0
    }
}

fn add(x: u8,y: u8) -> u8 {
    x^y
}

fn inv(x: u8) -> u8 {
   let ix = (x as usize) & 0xff;
   let lx = (LTAB[ix] as usize) & 0xff;
   PTAB[255-lx]
}

/* Lagrange interpolation */
fn interpolate(n: usize, x: &[u8], y: &[u8]) -> u8 {
    let mut yp=0 as u8;
    for i in 0..n {
        let mut p=1 as u8;
        for j in 0..n {
            if i!=j {
                p=mul(p,mul(x[j],inv(add(x[i],x[j]))));
            }
        }
        yp=add(yp,mul(p,y[i]));
    }
    yp
}

impl<'a> SHARE<'a> {

/* Return a share of M */
/* input id - Unique share ID */
/* input nsr - Number of shares required for recovery */
/* input Message M to be shared */
/* input Random number generator rng to be used */
/* return share structure */
// must bind lifetime of the byte array stored by structure, to lifetime of s
    pub fn new(ident: usize,numshare: usize,s: &'a mut [u8],m: &[u8], rng: &mut impl RAND) -> SHARE<'a> {
        if ident<1 || ident>=256 || numshare<2 || numshare>=256 {
            return SHARE{id:0,nsr:0,b:s};
        }
        let len=m.len();
        for j in 0..len {
            let mut x=ident as u8;
            s[j]=m[j];
            for _ in 1..numshare {
                s[j]=add(s[j],mul(rng.getbyte(),x));
                x=mul(x,ident as u8);
            }
        }
        SHARE{id: ident as u8,nsr: numshare as u8,b:s}
    }
/* recover M from shares */
    pub fn recover(m: &mut [u8],s: &[SHARE]) {
        let len=s[0].b.len();
        let nsr=s[0].nsr as usize;
        if nsr!=s.len() {
            return;
        }
        for i in 1..nsr {
            if s[i].nsr as usize != nsr || s[i].b.len()!=len {
                return;
            }
        }
        let mut x: [u8; 256] = [0; 256];
        let mut y: [u8; 256] = [0; 256];

        for j in 0..len {
            for i in 0..nsr {
                x[i]=s[i].id;
                y[i]=s[i].b[j];
            }
            m[j]=interpolate(nsr,&x,&y);
        }
    }
}