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copied!<p>A much shorter and safer answer - <strong>don't write your own password mechanism at all</strong>, use a tried and tested mechanism.</p> <ul> <li>PHP 5.5 or higher: <a href="http://php.net/manual/en/function.password-hash.php" rel="noreferrer">password_hash()</a> is good quality and part of PHP core.</li> <li>Older PHP versions: OpenWall's <a href="http://www.openwall.com/phpass/" rel="noreferrer">phpass</a> library is much better than most custom code - used in WordPress, Drupal, etc.</li> </ul> <p>Most programmers just don't have the expertise to write crypto related code safely without introducing vulnerabilities.</p> <p><strong>Quick self-test:</strong> what is password stretching and how many iterations should you use? If you don't know the answer, you should use <code>password_hash()</code>, as password stretching is now a critical feature of password mechanisms due to much faster CPUs and the use of <a href="http://blog.crackpassword.com/2012/07/accelerating-password-recovery-the-addition-of-fpga/" rel="noreferrer">GPUs and FPGAs</a> to crack passwords at rates of <a href="http://en.wikipedia.org/wiki/Password_cracking#Time_needed_for_password_searches" rel="noreferrer">billions of guesses per second</a> (with GPUs).</p> <p>For example, you can <a href="http://arstechnica.com/security/2012/12/25-gpu-cluster-cracks-every-standard-windows-password-in-6-hours/" rel="noreferrer">crack all 8-character Windows passwords in 6 hours</a> using 25 GPUs installed in 5 desktop PCs. This is brute-forcing i.e. enumerating and checking <em>every 8-character Windows password</em>, including special characters, and is not a dictionary attack. That was in 2012, as of 2018 you could use fewer GPUs, or crack faster with 25 GPUs.</p> <p>There are also many rainbow table attacks on Windows passwords that run on ordinary CPUs and are very fast. All this is because Windows <em>still</em> <a href="https://superuser.com/a/118279/90231">doesn't salt or stretch</a> its passwords, <a href="https://www.guidingtech.com/61991/cracking-windows-10-password-prevent/" rel="noreferrer">even in Windows 10</a> - don't make the same mistake as Microsoft did!</p> <p><strong>See also:</strong> </p> <ul> <li><a href="https://stackoverflow.com/questions/1581610/how-can-i-store-my-users-passwords-safely/1581919#1581919">excellent answer</a> with more about why <code>password_hash()</code> or <code>phpass</code> are the best way to go.</li> <li><a href="https://www.nccgroup.trust/us/about-us/newsroom-and-events/blog/2015/march/enough-with-the-salts-updates-on-secure-password-schemes/" rel="noreferrer">good blog article</a> giving recommmended 'work factors' (number of iterations) for main algorithms including bcrypt, scrypt and PBKDF2.</li> </ul>

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