StackOverflow2013

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PO
primarykey
Id
20841646
data
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0
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2013-12-30T14:37:11.213
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2013-12-30T14:37:11.213
LastEditDate
2017-03-17T13:14:45.960
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32775
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3691116
PostTypeId
2
Score
3
ViewCount
0
LastEditorDisplayName
text
Body
I asked this question several years ago and, since then, my knowledge of this topic has improved. First of all, I mentioned I wanted random numbers for a login system. Login systems are security mechanisms. This means that any random number generators that the login system relies on should be cryptographically secure. PHP's <code>rand</code> and <code>mt_rand</code> are not cryptographically secure. In these cases, it's best to be safe than sorry. There are random number generators designed specifically to be secure, notably <a href="http://www.php.net/manual/en/function.openssl-random-pseudo-bytes.php" rel="nofollow noreferrer"><code>openssl_random_pseudo_bytes</code></a> (which is unfortunately not always available -- you must enable the OpenSSL extension for it to work). On *NIX systems (such as Linux), bytes read from <code>/dev/urandom</code> <a href="https://security.stackexchange.com/questions/3936/is-a-rand-from-dev-urandom-secure-for-a-login-key">can be used</a> as well. Unfortunately (for the purposes of this question), both of these approaches return binary data instead of hexadecimal. Fortunately, PHP already has a function to fix this for us, <a href="http://www.php.net/manual/en/function.bin2hex.php" rel="nofollow noreferrer"><code>bin2hex</code></a>, which works for strings of any length. So here's how the code would look like: <pre><code>function generate_secure_random_hex_string($length) { // $length should be an even, non-negative number. // Because each byte is represented as two hex digits, we'll need the binary // string to be half as long as the hex string. $binary_length = $length / 2; // First, we'll generate the random binary string. $random_result = openssl_random_pseudo_bytes($binary_length, $cstrong); if (!$cstrong) { // The result is not cryptographically secure. Abort. // die() is just a placeholder. // There might be better ways to handle this error. die(); } //Convert the result to hexadecimal return bin2hex($random_result); } // Example: echo generate_secure_random_hex_string(32); </code></pre>
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1. POBig random number generation
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1. PTAnswer
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1. USCommunity
UserOwnerUserId
1. USluiscubal
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