openssl_random_pseudo_bytes()

(PHP 5 >= 5.3.0, PHP 7)

生成一个伪随机字节串

说明

openssl_random_pseudo_bytes(int $length[,bool &$crypto_strong]): string

生成一个伪随机字节串string，字节数由$length参数指定。

通过$crypto_strong参数可以表示在生成随机字节的过程中是否使用了强加密算法。返回值为FALSE的情况很少见，但已损坏或老化的有些系统上会出现。

参数

$length: 所需字节串的长度，必须为正整数。PHP会试着将该参数转换为非空整数来使用它。
$crypto_strong: 如果传递到该函数中，将会保存为一个boolean值来表明是否使用了“强加密”，如果被用于GPG和密码之类的将返回TRUE, 否则返回FALSE

返回值

成功，返回生成的字节串string，或者在失败时返回FALSE.

范例

openssl_random_pseudo_bytes()范例：

<?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;
}
?>

以上例程的输出类似于：

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)

参见

random_bytes()Generates cryptographically secure pseudo-random bytes
bin2hex()函数把包含数据的二进制字符串转换为十六进制值
crypt()单向字符串散列
mt_rand()生成更好的随机数
uniqid()生成一个唯一ID

Here's an example to show the distribution of random numbers as an image. Credit to Hayley Watson at the mt_rand page for the original comparison between rand and mt_rand.
rand is red, mt_rand is green and openssl_random_pseudo_bytes is blue.
NOTE: This is only a basic representation of the distribution of the data. Has nothing to do with the strength of the algorithms or their reliability.
<?php
header("Content-type: image/png");
$sizex=800;
$sizey=800;
$img = imagecreatetruecolor(3 * $sizex,$sizey);
$r = imagecolorallocate($img,255, 0, 0);
$g = imagecolorallocate($img,0, 255, 0);
$b = imagecolorallocate($img,0, 0, 255);
imagefilledrectangle($img, 0, 0, 3 * $sizex, $sizey, imagecolorallocate($img, 255, 255, 255));
$p = 0;
for($i=0; $i < 100000; $i++) {
  $np = rand(0,$sizex);
  imagesetpixel($img, $p, $np, $r);
  $p = $np;
}
$p = 0;
for($i=0; $i < 100000; $i++) {
  $np = mt_rand(0,$sizex);
  imagesetpixel($img, $p + $sizex, $np, $g);
  $p = $np;
}
$p = 0;
for($i=0; $i < 100000; $i++) {
  $np = floor($sizex*(hexdec(bin2hex(openssl_random_pseudo_bytes(4)))/0xffffffff));
  imagesetpixel($img, $p + (2*$sizex), $np, $b);
  $p = $np;
}
imagepng($img);
imagedestroy($img);
?>

[Editor's note: the bug has been fixed as of PHP 5.4.44, 5.5.28 and PHP 5.6.12]
Until PHP 5.6 openssl_random_pseudo_bytes() did NOT use a "cryptographically strong algorithm"! 
See bug report https://bugs.php.net/bug.php?id=70014 and the corresponding source code at https://github.com/php/php-src/blob/php-5.6.10/ext/openssl/openssl.c#L5408

Another replacement for rand() using OpenSSL.
Note that a solution where the result is truncated using the modulo operator ( % ) is not cryptographically secure, as the generated numbers are not equally distributed, i.e. some numbers may occur more often than others.
A better solution than using the modulo operator is to drop the result if it is too large and generate a new one.
<?php
function crypto_rand_secure($min, $max) {
    $range = $max - $min;
    if ($range == 0) return $min; // not so random...
    $log = log($range, 2);
    $bytes = (int) ($log / 8) + 1; // length in bytes
    $bits = (int) $log + 1; // length in bits
    $filter = (int) (1 << $bits) - 1; // set all lower bits to 1
    do {
      $rnd = hexdec(bin2hex(openssl_random_pseudo_bytes($bytes, $s)));
      $rnd = $rnd & $filter; // discard irrelevant bits
    } while ($rnd >= $range);
    return $min + $rnd;
}
?>

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;
  }
?>

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

Getting an integer value from a given range with an even distribution:
This function I created to solve the problem of modulo results causing overlap of ranged results (which gave an uneven distribution).
What I mean for those not as familiar with the problem: 
Using bytes for base 256 (base 16) and attempting to find a value in a range of values that may be for example 10-20 (a spread of 11) will not divide evenly, so values (using mod) will overlap and give more priority to some numbers than others.
Instead of calculating based on byte values, I used the byte values as keys to sort. This is very fast, and does not require large multiplications of data space that easily go over the value of Max Int.
Additionally: To make the user-supplied arguments not care about order I am using a handy swap function I found in the wild in conjunction with my function below.
// swap function
function swap(&$a,&$b) { list($a,$b)=array($b,$a); } // swap 2 variables-- no temp variable needed!
// function to get a random value within a given range of integers
  
function get_secure_random_ranged_value($max=99, $min=0) // handles 1 or 2 arguments, order does not matter
{
  $sortarray = array();
  $lo = (int)$min; 
  $hi = (int)$max;
  if ($lo > $hi) swap($lo,$hi); 
  $data_range = abs($hi - $lo) + 1; // +1 includes both the lowest 'zero' value and highest value of range
  $bytes_per_key = 4; // Max: ffff hex = 4,294,967,296 dec (over 4 billion) -- large span of random values covers massive datasets
  $num_bytes = $data_range * $bytes_per_key; 
  $byte_string = (bin2hex(openssl_random_pseudo_bytes($num_bytes))); // only one call needed to get string of bytes
  $byte_blocksize = $bytes_per_key << 1; // shift multiply by 2 since a byte is 2 characters wide
  
  while ($key = substr($byte_string,0,$byte_blocksize)) { // get next byte block from string
    $byte_string = substr($byte_string,$byte_blocksize); // remove selected byte block from string
    $sortarray[]=$key; // populate the array with keys temporarily as array values
  } 
    
  $sortarray = array_flip($sortarray); // swap to use the byte values as keys 
  ksort($sortarray); // randomize by keys
  return array_shift($sortarray) + $lo; // grab top value from array and add it to the lowest value in the range  
} 
//
// example getting values from 0 to 21:
//
  
for ($i=1;$i<=10;$i++) { $rnd = get_secure_random_ranged_value(21); echo "-> result: ".($rnd)." <br />\n"; } 
//
// example getting values from 14 to 21:
//
for ($i=1;$i<=10;$i++) { $rnd = get_secure_random_ranged_value(14,21); echo "-> result: ".($rnd)." <br />\n"; } 
//
// sample results from 14-21
//
-> result: 14
-> result: 18
-> result: 20
-> result: 15
-> result: 20
-> result: 16
-> result: 21
-> result: 15
-> result: 16
-> result: 17

Remember to request at very least 8 bytes of entropy, ideally 32 or 64, to avoid possible theorical bruteforce attacks.

After the fix of insecure number generation here:
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2015-8867
This function as well as the text here needs an update. I believe this function is safe to use in FIPS compliant apps as well as it now used RAND_bytes instead of the insecure RAND_pseudo_bytes().

Another way to get random 32bit ints:
function myRand($max){
  do{
    $result = floor($max*(hexdec(bin2hex(openssl_random_pseudo_bytes(4)))/0xffffffff));
  }while($result == $max);
  return $result;
}

if unavailable use this with core functions... maybe not as secure and optimized (any help?), but practical
<?php
$bytes = '';
while (strlen($bytes) < $lenght)
 $bytes .= chr(mt_rand(0, 255));
?>

Why does bin2hex return twice as many characters as bytes?