Finds Letter Frequencies In Text And Outputs Likely Letters

breaker.js

var freq = require("freq"),
    fs = require("fs"),
    eng = {
         'e': 13.11,
         't': 10.47,
         'a': 8.15,
         'o': 8.00,
         'n': 7.10,
         'r': 6.83,
         'i': 6.35,
         's': 6.10,
         'h': 5.26,
         'd': 3.79,
         'l': 3.39,
         'f': 2.92,
         'c': 2.76,
         'm': 2.54,
         'u': 2.46,
         'g': 1.99,
         'y': 1.98,
         'p': 1.98,
         'w': 1.54,
         'b': 1.44,
         'v': 0.92,
         'k': 0.42,
         'x': 0.17,
         'j': 0.13,
         'q': 0.12,
         'z': 0.08
      },
      bi = {
        'th': 168,
        'he': 132,
        'an': 92,
        're': 91,
        'er': 88,
        'in': 86,
        'on': 71,
        'at': 68,
        'nd': 61,
        'st': 53,
        'es': 52,
        'en': 51,
        'of': 49,
        'te': 46,
        'ed': 46
    };

var file = fs.readFileSync(process.argv[2], "utf8").replace(/[^a-z]/g,"");
    bi_s = freq.sortObj(bi),
    c_s = freq.sortObj(eng),
    mbi_s = freq.bigrams(file),
    mc_s = freq.charFreq(file);

console.log(mc_s);

var map = {},
    bi_map = {};

// construct the mapping between letters in the
// ciphertext and the distribution of letter in english
for(var i = 0, len = c_s.length; i < len; i++){
    if(c_s[i] && mc_s[i])
        map[mc_s[i].node] = c_s[i].node;
}

// same as above, except with bigrams
for(var i = 0, len = bi_s.length; i < len; i++){
    if(bi_s[i] && mbi_s[i])
        bi_map[mbi_s[i].node] = bi_s[i].node;
}

// refine the letter to letter mapping by cross referencing
// it with the bigram mapping

var rpl_str = function(str){
    var keys = Object.keys(map);

    for(var i = 0, len = keys.length; i < len; i++){
        str = str.replace(new RegExp(keys[i], "g"), map[keys[i]]);
    }

    return str;
}

console.log(map);
console.log(bi_map);

var keys = Object.keys(bi_map);
for(var i = 0, len = keys.length; i < len; i++){
    if(keys[i] !== (rpl_str(keys[i][0]) + rpl_str(keys[i][1]))){
        //console.log(keys[i]);
        //console.log((rpl_str(keys[i][0]) + rpl_str(keys[i][1])));
    }
}

// replace the bigrams/letter in the ciphertext with the
// proper ones based on the mapping
/*
var keys = Object.keys(bi_map);
for(var i = 0, len = keys.length; i < len; i++){
    file = file.replace(new RegExp(keys[i], "g"), bi_map[keys[i]]);
}



console.log(file);
*/