zx2c4
commented
6 years ago This is probably what you want:
/* Copyright (C) 2017 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved. */
#include <QString>
#include <QRandomGenerator>
quint32 boundedRandom(quint32 bound)
{
if (bound < 2)
return 0;
quint32 randval;
const quint32 max_mod_bound = (1 + ~bound) % bound;
do
randval = QRandomGenerator::system()->generate();
while (randval < max_mod_bound);
return randval % bound;
}
QString generateRandomPassword(const QString &charset, unsigned int length)
{
QString out;
for (unsigned int i = 0; i < length; ++i)
out.append(charset.at(boundedRandom(charset.length())));
return out;
}You may use this code under the current license of the project at the time of this comment, provided you retain the copyright header.
annejan
innir
Serphentas
carnil
noloader
The current way of generating passwords is insecure. All passwords that have been generated with QtPass in the past must be regenerated and changed.
Here is the current password generation function:
The problem here is that modulo will not uniformly distribute that set. The proper way to do things is to just throw away values that are out of bounds. You could try to do the calculation correctly to uniformly stretch or compress, but it's hard to get right, so it's best to just discard numbers outside the set and try again.
Secondly, and more critically, here is the implementation of
Util::rand:Unfortunately, using a non-cryptographically secure random number generator like libc's
rand()is problematic -- future outputs can be derived from knowing only a handful of past outputs -- and seeding that deterministic rng withcurrentTime()->msec()is even more dangerous. Not only is the current time a guessable/bruteforcable parameter, but the documentation forQTime::msecactually indicates that this is merely the "the millisecond part (0 to 999) of the time", which means there are only 1000 possibilities of generated sequences of passwords.This is as bad as it gets, in terms of password manager password generation.
The proper fix is to use Qt 5.10's
QRandomGenerator::system(). If 5.10 is not available to you, use/dev/urandomon Mac/Linux andRtlGenRandomon Windows.The password generator inside pass(1) itself is implemented like this: