crypto-keygen-suite/keyGen/ciphers/affineciphergenerator.js

Key generation utilities for cryptographic operations. YES I RENAMED IT. SIX STATE PROTOCOL!!! See its folder for all <3

#!/usr/bin/env node

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

const m = 26;

function modInverse(a, m) {
    a = ((a % m) + m) % m;
    for (let x = 1; x < m; x++) {
        if ((a * x) % m === 1) return x;
    }
    throw new Error(`No modular inverse for a = ${a} under mod ${m}.`);
}

function encrypt(text, a, b) {
    return text
        .toUpperCase()
        .replace(/[^A-Z]/g, '')
        .split('')
        .map(char => {
            const x = char.charCodeAt(0) - 65;
            const y = (a * x + b) % m;
            return String.fromCharCode(y + 65);
        })
        .join('');
}

function decrypt(text, a, b) {
    const aInv = modInverse(a, m);
    return text
        .toUpperCase()
        .replace(/[^A-Z]/g, '')
        .split('')
        .map(char => {
            const y = char.charCodeAt(0) - 65;
            const x = ((aInv * (y - b + m)) % m + m) % m;
            return String.fromCharCode(x + 65);
        })
        .join('');
}

yargs(hideBin(process.argv))
    .command(
        'encrypt',
        'Encrypt using Affine cipher',
        y => y
            .option('a', { describe: 'Key a (must be coprime with 26)', demandOption: true, type: 'number' })
            .option('b', { describe: 'Key b', demandOption: true, type: 'number' })
            .option('text', { describe: 'Plaintext', demandOption: true, type: 'string' }),
        argv => {
            try {
                console.log('Encrypted:', encrypt(argv.text, argv.a, argv.b));
            } catch (err) {
                console.error('❌ Error:', err.message);
            }
        }
    )
    .command(
        'decrypt',
        'Decrypt using Affine cipher',
        y => y
            .option('a', { describe: 'Key a (must be coprime with 26)', demandOption: true, type: 'number' })
            .option('b', { describe: 'Key b', demandOption: true, type: 'number' })
            .option('text', { describe: 'Ciphertext', demandOption: true, type: 'string' }),
        argv => {
            try {
                console.log('Decrypted:', decrypt(argv.text, argv.a, argv.b));
            } catch (err) {
                console.error('❌ Error:', err.message);
            }
        }
    )
    .demandCommand()
    .strict()
    .help()
    .argv;