shamirs-secret-sharing-ts/dist/lagrange.js

A simple implementation of Shamir's Secret Sharing configured to use a finite field in GF(2^8) with 128 bit padding

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
const table_1 = require("./table");
const constants_1 = require("./constants");
function lagrange(x, p) {
    const n = constants_1.MAX_SHARES;
    let product = 0;
    let sum = 0;
    for (let i = 0; i < p[0].length; ++i) {
        if (p[1][i]) {
            product = table_1.logs[p[1][i]];
            for (let j = 0; j < p[0].length; ++j) {
                // m != j
                if (i !== j) {
                    if (x === p[0][j]) {
                        product = -1;
                        break;
                    }
                    const a = table_1.logs[x ^ p[0][j]] - table_1.logs[p[0][i] ^ p[0][j]];
                    product = (product + a + n) % n;
                }
            }
            sum = -1 === sum ? sum : sum ^ table_1.exps[product];
        }
    }
    return sum;
}
exports.lagrange = lagrange;