openssl_random_pseudo_bytes

(PHP 5 >= 5.3.0)

openssl_random_pseudo_bytes — Generate a pseudo-random string of bytes

说明

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

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.

参数

length: 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.
crypto_strong: 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

返回值

Returns the generated string of bytes on success, 或者在失败时返回 FALSE .

范例

Example #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 ;
}
 ?>

以上例程的输出类似于：

Lengths: Bytes: -1 and Hex: 0
string(0) ""
NULLLengths: Bytes: 0 and Hex: 0
string(0) ""
NULLLengths: 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ASCII字符的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

用户评论:

[#1] nahun@telemako [2013-09-13 07:25:30]

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); ?>

[#2] Anonymous [2012-05-06 00:17:49]

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;
}

[#3] christophe dot weis at statec dot etat dot lu [2011-06-09 00:09:56]

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; } ?>

[#4] crrodriguez at opensuse dot org [2011-01-19 09:32:52]

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

[#5] acatalept at gmail [2011-01-11 11:24:43]

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

[#6] Tyler Larson [2009-08-21 14:29:28]

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; } ?>