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(PHP 5 >= 5.3.0)
openssl_random_pseudo_bytes — Generate a pseudo-random string of bytes
Generates a string of pseudo-random bytes, with the number of bytes determined by the length parameter.
It also indicates if a cryptographically strong algorithm was used to produce the pseudo-random bytes, and does this via the optional crypto_strong parameter. It's rare for this to be FALSE, but some systems may be broken or old.
The length of the desired string of bytes. Must be a positive integer. PHP will try to cast this parameter to a non-null integer to use it.
If passed into the function, this will hold a boolean value that determines if the algorithm used was "cryptographically strong", e.g., safe for usage with GPG, passwords, etc. TRUE if it did, otherwise FALSE
Returns the generated string of bytes on success, Im Fehlerfall wird FALSE zurückgegeben..
Beispiel #1 openssl_random_pseudo_bytes() example
<?php
for ($i = -1; $i <= 4; $i++) {
$bytes = openssl_random_pseudo_bytes($i, $cstrong);
$hex = bin2hex($bytes);
echo "Lengths: Bytes: $i and Hex: " . strlen($hex) . PHP_EOL;
var_dump($hex);
var_dump($cstrong);
echo PHP_EOL;
}
?>
Das oben gezeigte Beispiel erzeugt eine ähnliche Ausgabe wie:
Lengths: Bytes: -1 and Hex: 0 string(0) "" NULL Lengths: Bytes: 0 and Hex: 0 string(0) "" NULL Lengths: Bytes: 1 and Hex: 2 string(2) "42" bool(true) Lengths: Bytes: 2 and Hex: 4 string(4) "dc6e" bool(true) Lengths: Bytes: 3 and Hex: 6 string(6) "288591" bool(true) Lengths: Bytes: 4 and Hex: 8 string(8) "ab86d144" bool(true)
FYI, openssl_random_pseudo_bytes() can be incredibly slow under Windows, to the point of being unusable. It frequently times out (>30 seconds execution time) on several Windows machines of mine.
Apparently, it's a known problem with OpenSSL (not PHP specifically).
See: http://www.google.com/search?q=openssl_random_pseudo_bytes+slow
a simple way to generate a random password is:
<?php
$password = base64_encode(openssl_random_pseudo_bytes($length, $strong));
?>
this function generates a password with a fallback to mt_rand() if no openssl is available:
<?php
/**
* generates a random password, uses base64: 0-9a-zA-Z/+
* @param int [optional] $length length of password, default 24 (144 Bit)
* @return string password
*/
function generatePassword($length = 24) {
if(function_exists('openssl_random_pseudo_bytes')) {
$password = base64_encode(openssl_random_pseudo_bytes($length, $strong));
if($strong == TRUE)
return substr($password, 0, $length); //base64 is about 33% longer, so we need to truncate the result
}
//fallback to mt_rand if php < 5.3 or no openssl available
$characters = '0123456789';
$characters .= 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz/+';
$charactersLength = strlen($characters)-1;
$password = '';
//select some random characters
for ($i = 0; $i < $length; $i++) {
$password .= $characters[mt_rand(0, $charactersLength)];
}
return $password;
}
?>
note: openssl_random_pseudo_bytes() is considerably slower than mt_rand.
Here's a drop-in replacement for rand() using OpenSSL as your PRNG:
<?php
function crypto_rand($min,$max) {
$range = $max - $min;
if ($range == 0) return $min; // not so random...
$length = (int) (log($range,2) / 8) + 1;
return $min + (hexdec(bin2hex(openssl_random_pseudo_bytes($length,$s))) % $range);
}
?>
If you don't have this function but you do have OpenSSL installed, you can always fake it:
<?php
function openssl_random_pseudo_bytes($length) {
$length_n = (int) $length; // shell injection is no fun
$handle = popen("/usr/bin/openssl rand $length_n", "r");
$data = stream_get_contents($handle);
pclose($handle);
return $data;
}
?>
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