random-string.js

#!/usr/bin/node
var targetEntropy = parseFloat(process.argv[2]);
var charSet = process.argv[3] && process.argv[3].toLowerCase();
var testStrength = parseInt(process.argv[4]) || 16384;

var filter = () => true;

switch (charSet) {
    case 'alphanum': filter = isAlphaNum; break;
}

var crypto = require('crypto');

function getOneChar() {
    while (true) {
        var t = crypto.randomBytes(1)[0];
        if (t >= 95 * 2) continue;
        var c = String.fromCharCode(t % 95 + 32);
        if (!filter(c)) continue;
        return c;
    }
}

// entropy calculate
var tot = 114514;
var counts = {};
for (var i = 0; i < tot; i++) {
    var c = getOneChar();
    counts[c] = counts[c] || 0;
    counts[c]++;
}
var entropy = 0;
for (var c in counts) {
    var p = counts[c] / tot;
    entropy += p * (-Math.log2(p));
}

var output = '';
var curEntropy = 0;
var rem = 0;
while (curEntropy < targetEntropy) {
    var c = getOneChar();
    output += c;
    curEntropy += entropy;
}
process.stdout.write(output);

console.error('\nentropy:', curEntropy);

function isAlphaNum(c) {
    if (c >= '0' && c <= '9') return true;
    if (c >= 'A' && c <= 'Z') return true;
    if (c >= 'a' && c <= 'z') return true;
    return false;
}