keygentoolshed/keyGen/shamir/computeSecret.js

Key generation utilities for cryptographic operations. QUANTUM ENCRYPTION FOLDER UPDATE!!! See its folder for all <3

import fs from 'fs';
import yargs from 'yargs/yargs';
import { hideBin } from 'yargs/helpers';

function computeSecret(shares) {
    const k = shares.length; 
    let secret = 0; 

    for (let i = 0; i < k; i++) {
        const [x_i, y_i] = shares[i];

        let numerator = 1;
        let denominator = 1;

        for (let j = 0; j < k; j++) {
            if (i !== j) {
                const [x_j] = shares[j];
                numerator = (numerator * (-x_j)) % 256; // Modulo can be adjusted based on the secret space
                denominator = (denominator * (x_i - x_j)) % 256; // Modulo can be adjusted based on the secret space
            }
        }

        const lagrangeBasis = (numerator * modInverse(denominator, 256)) % 256; // Modulo can be adjusted based on the secret space
        secret = (secret + (lagrangeBasis * y_i)) % 256; // Modulo can be adjusted based on the secret space
    }

    return secret;
}

function modInverse(a, m) {
    let m0 = m, t, q;
    let x0 = 0, x1 = 1;

    if (m === 1) return 0;

    while (a > 1) {
        q = Math.floor(a / m);
        t = m;

        m = a % m;
        a = t;
        t = x0;

        x0 = x1 - q * x0;
        x1 = t;
    }

    if (x1 < 0) x1 += m0;

    return x1;
}

const argv = yargs(hideBin(process.argv))
    .usage('Usage: $0 --secret [shares]')
    .option('secret', {
        alias: 's',
        describe: 'Specify the shares in the format x1:y1,x2:y2,...',
        type: 'string',
        demandOption: true 
    })
    .help()
    .argv;

const sharesInput = argv.secret.split(',').map(share => {
    const [x, y] = share.split(':').map(Number);
    return [x, y];
});

// Compute the secret
const secret = computeSecret(sharesInput);
console.log(`Reconstructed secret: ${secret}`);