keygentoolshed/keyGen/shamir/reconstructSecrets.js

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

import { program } from 'commander';

// Function to compute modular inverse using Extended Euclidean Algorithm
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;
}

function reconstructSecret(shares) {
    const threshold = shares.length;
    const secret = shares.reduce((acc, { share, index }) => {
        let product = shares.reduce((prod, { index: j }) => {
            if (index !== j) {
                // Calculate the Lagrange basis polynomial
                return (prod * (0 - j) * modInverse(index - j, 256)) % 256; // Use multiplication and modular inverse
            }
            return prod;
        }, 1);
        const term = (share * product) % 256; // Calculate the term for this share
        console.log(`Share: ${share}, Index: ${index}, Term: ${term}`); // Log the term for each share
        return (acc + term) % 256; 
    }, 0);
    return secret;
}

function main() {
    program
        .option('--shares <shares>', 'Comma-separated list of shares in the format index:share', (value) => {
            return value.split(',').map(pair => {
                const [index, share] = pair.split(':').map(Number);
                return { index, share };
            });
        });

    program.parse(process.argv);
    const options = program.opts();

    if (!options.shares) {
        console.error('Please provide shares in the format index:share.');
        process.exit(1);
    }

    const secret = reconstructSecret(options.shares);
    console.log('Reconstructed Secret:', secret);
}

main();