binary_rank.js

const fs = require('fs');

if (process.argv.length != 3) {
    console.log('Usage: node binary_rank <filename>');
    process.exit(1);
}

const filename = process.argv[2];

const isValidAscii = (b) => {
    return b >= 32 && b <= 126;
}

const decrypt = (data) => {
    for (let key = 0; key < 256; key++) {
        let isValid = true;
        let lastIndex = 0;

        for (let i = 0x4C; i < data.length; i++) {
            const decrypted = data.charCodeAt(i) ^ key;

            if (!isValidAscii(decrypted)) {
                isValid = false;
                lastIndex = i;
                console.log(`Invalid character: ${decrypted} at index ${i}`);
                break;
            }
        }

        console.log(`Key: ${key}, Last index: ${lastIndex}`);

        if (isValid) {
            console.log(`Key: ${key}`);
            break;
        }
    }
}

fs.readFile(filename, 'binary', (err, data) => {
    if (err) {
        console.log(`Error reading file: ${err}`);
        process.exit(1);
    }

    decrypt(data);

    const ranks = new Map();

    for (let i = 0; i < data.length; i++) {
        const b = data[i];

        if (ranks.has(b)) {
            ranks.set(b, ranks.get(b) + 1);
        } else {
            ranks.set(b, 1);
        }
    }

    const sortedRanks = Array.from(ranks.entries()).sort((a, b) => b[1] - a[1]);

    for (let [byte, count] of sortedRanks) {
        let hex = byte.charCodeAt(0).toString(16);
        console.log(`${hex}: ${count}`);
    }
});