tryAll

isEnglish.js

'use strict'
const fs = require('fs')

// Save this list as `eng_10k.txt`: https://raw.githubusercontent.com/first20hours/google-10000-english/master/google-10000-english.txt
const _getFrequencyList = () => {
    const frequencyList = fs.readFileSync(`${__dirname}/eng_10k.txt`).toString().split('\n').slice(1000)
    const dict = {};
    frequencyList.forEach(word => {
        // Ignore weird consonant clusters
        // match returns `null` if `word` contains no vowels
        if (!word.match(/[aeuoi]/gi)) {
            return;
        }

        dict[word] = word;
    })
    return dict;
}

const isEnglish = string => {
    // Default threshold for how many English words we need before we consider the sentence "maybe English"
    const threshold = 3;
    if (string.split(/\s/).length < 6) {
        // If this isn't a long enough sentence, be conservative: assume it's english
        return true;
    } else {
        let count = 0;
        const frequencyList = _getFrequencyList();
        string.split(/\s/).forEach(function (string) {
            const adjusted = string.toLowerCase().replace(/\./g, '')
            if (frequencyList[adjusted]) {
                count += 1;
            }
        })

        return count > threshold;
    }
}

module.exports = isEnglish;

tryAll.js

const caesar = require('./caesar');

// Brute-force attack on Caesar's (non-)cipher
const tryAll = function (encryptedString) {
    // The Caesar cipher 
    const decryptionAttempts = []
    while (decryptionAttempts.length < 24) {
        const decryptionKey = -decryptionAttempts.length;
        const decryptionAttempt = caesar(encryptedString, decryptionKey);
        decryptionAttempts.push(decryptionAttempt)
    }
    return decryptionAttempts;
};

const encryptedString = 'xt ny itjx.'
const decryptionAttempts = tryAll(encryptedString);

module.exports = tryAll;