mt_getrandmax
Re: euxneks at NOSPAMgmail dot com
You might also want to add STR_PAD_LEFT and have:
<?php
echo '#' . str_pad( base_convert( mt_rand(0, ( 255*255*255) ), 10, 16 ), 6, '0', STR_PAD_LEFT) . "\n";
?>
mt_rand
(PHP 4, PHP 5)
mt_rand — 향상된 난수를 생성합니다.
설명
int mt_rand
([ int $min
], int $max
)
사용해 온 libc들의 많은 난수 생성기는 이상하거나, 특성을 알 수 없거나, 느렸습니다. 기본적으로, PHP는 rand() 함수에서 libc 난수 생성기를 이용합니다. mt_rand()는 이를 대체합니다. » Mersenne Twister를 사용하는 확실한 특성을 가진 난수 생성기를 이용합니다. 이것은 평균적인 libc 제공의 난수 생성기에 비해 4배 정도 빠릅니다.
선택적인 min , max 인자 없이 호출하면, mt_rand()는 0과 RAND_MAX 사이의 모조 난수를 반환합니다. 예를 들어, 5와 15(포함)사이의 난수를 원할 경우에는, mt_rand (5, 15)로 사용합니다.
Example#1 mt_rand() 예제
<?php
echo mt_rand() . "\n";
echo mt_rand() . "\n";
echo mt_rand(5, 15);
?>
위 예제의 출력 예는:
1604716014 1478613278 6
Note: PHP 4.2.0부터 srand()나 mt_srand()를 이용한 난수값 생성기 초기화를 할 필요가 없습니다. 자동적으로 이루어집니다.
Note: 3.0.7 이전 버전에서는 max 의 의미는 range 였습니다. 이 버전에서 위에 든 예처럼 5에서 15 사이의 난수를 얻기 위해서는 mt_rand (5, 11)로 사용해야 합니다.
참고: mt_srand(), mt_getrandmax(), rand().
add a note
User Contributed Notesmt_rand
rt
27-Aug-2008 05:14
27-Aug-2008 05:14
euxneks at NOSPAMgmail dot com
18-Aug-2008 03:11
18-Aug-2008 03:11
Re: keith at ourwebsite dot ca
Here's another way to do it, in one line :)
<?php
echo '#' . str_pad( base_convert( mt_rand(0, ( 255*255*255) ), 10, 16 ), 6, '0' ) . "\n";
?>
str_pad is there in case mt_rand chooses a number that will generate a hex value with less than 6 characters. (you could leave that out but it's not a very clean way to write the hex colors is it :)
keith at ourwebsite dot ca
17-Jul-2008 03:16
17-Jul-2008 03:16
This is how I generate a random colour for backgrounds, graphs, text colour etc.
<?
$total = "9";
$start = "0";
$randcolour = mt_rand($start, $total);
$randcolour .= mt_rand($start, $total);
$randcolour .= mt_rand($start, $total);
$randcolour .= mt_rand($start, $total);
$randcolour .= mt_rand($start, $total);
$randcolour .= mt_rand($start, $total);
?>
<table width="200px" border="0" cellspacing="10" cellpadding="0" bgcolor="#<? echo $randcolour; ?>">
<tr>
<td>This table has a random background colour</td>
</tr>
</table>
Mark Seecof
05-Jun-2008 11:31
05-Jun-2008 11:31
If you need some pseudorandom bits for security or cryptographic purposes (e.g.g., random IV for block cipher, random salt for password hash) mt_rand() is a poor source. On most Unix/Linux and/or MS-Windows platforms you can get a better grade of pseudorandom bits from the OS or system library, like this:
<?php
// get 128 pseudorandom bits in a string of 16 bytes
$pr_bits = '';
// Unix/Linux platform?
$fp = @fopen('/dev/urandom','rb');
if ($fp !== FALSE) {
$pr_bits .= @fread($fp,16);
@fclose($fp);
}
// MS-Windows platform?
if (@class_exists('COM')) {
// http://msdn.microsoft.com/en-us/library/aa388176(VS.85).aspx
try {
$CAPI_Util = new COM('CAPICOM.Utilities.1');
$pr_bits .= $CAPI_Util->GetRandom(16,0);
// if we ask for binary data PHP munges it, so we
// request base64 return value. We squeeze out the
// redundancy and useless ==CRLF by hashing...
if ($pr_bits) { $pr_bits = md5($pr_bits,TRUE); }
} catch (Exception $ex) {
// echo 'Exception: ' . $ex->getMessage();
}
}
if (strlen($pr_bits) < 16) {
// do something to warn system owner that
// pseudorandom generator is missing
}
?>
NB: it is generally safe to leave both the attempt to read /dev/urandom and the attempt to access CAPICOM in your code, though each will fail silently on the other's platform. Leave them both there so your code will be more portable.
Rocker
22-May-2008 07:24
22-May-2008 07:24
I think this will work faster.
<?php
function unique_random($Min,$Max,$num){
//this will swap min an max values if $Min>$Max
if ($Min>$Max) { $min=$Max; $max=$Min; }
else { $min=$Min; $max=$Max; }
//this will avoid to enter a number of results greater than possible results
if ($num>($max-$min)) $num=($max-$min);
$values=array();
$result=array();
for ($i=$min;$i<=$max;$i++) {
$values[]=$i;
}
for ($j=0;$j<$num;$j++){
$key=mt_rand(0,count($values)-1);
$result[]=$values[$key];
unset($values[$key]);
sort($values);
}
return $result;
}
?>
don_knotts at hotmail dot com
22-May-2008 04:58
22-May-2008 04:58
I forgot to add a side-note to my post about the unique random number function. If the array count is more than half of the random number max, the function could take a very long time to process, maybe even go into an infinite loop. The best way to avoid this is to set the max at twice the array count; i.e. if you want an array of 10 unique random numbers, the maximum random number needs to be at least 20. For my purposes, I have 50 pictures to choose from, and the function randomly picks 20 of them to display on the webpage, without displaying an image twice.
don_knotts at hotmail dot com
22-May-2008 03:57
22-May-2008 03:57
Here is a simple way to get UNIQUE random numbers, because if you are wanting random numbers, say, between 1 and 10, then you will get duplicates very often, so this function takes care of that. However, for a very large amount of numbers, this could be very slow. I use this to generate random pictures on a webpage so that I don't get the same picture twice, but it only picks from about 50 pictures.
// **************************************************
// generate UNIQUE random numbers between min and max
// uses the updated mt_rand() php function
// 'min' = minimum random number
// 'max' = maximum random number
// 'count' = how many numbers in the array
// returns array with random numbers
// error msg if count is greater than max
// **************************************************
function generateUniqueRandoms($min, $max, $count) {
if($count > $max) { // this prevents an infinite loop
echo "ERROR: The array count is greater than the random number maximum.<br>\n";
echo "Therefore, it is impossible to build an array of unique random numbers.<br>\n";
break;
}
$numArray = array();
for($i = 0; $i < $count; $i++) {
$numArray[$i] = mt_rand($min,$max); // set random number
for($j = 0; $j < $count; $j++) // for each number, check for duplicates
if($j != $i) // except for the one you are checking of course
if($numArray[$i] == $numArray[$j]) {
$numArray[$i] = mt_rand(1,10); // if duplicate, generate new random
$j = 0; // go back through and check new number
}
}
return $numArray;
} // end generateUniqueRandoms() ----------------------
// ****************************************************
Jonathon
17-Apr-2008 01:14
17-Apr-2008 01:14
Below, andrei suggested a function for generating a list of unique integers, randomly arranged. In response to a note below that his solution is inefficient, I'm providing an O(N) solution which should be much more efficient, yet still yield a good guarantee of producing randomly ordered integers.
<?php
function SwapShuffle($min, $max) {
$last = $max - $min;
for ($i=0; $i<=$last; $i++) {
$arr[$i] = $min + $i;
}
for ($run=0; $run<7; $run++) {
for ($i=0; $i<=$last; $i++) {
$target = mt_rand(0, $last);
$swap = $arr[$target];
$arr[$target] = $arr[$i];
$arr[$i] = $swap;
}
}
return $arr;
}
// Call as:
$result = SwapShuffle(10, 30);
foreach ($result as $num) {
echo "$num\n";
}
?>
geompse at yopmail dot com
29-Mar-2008 05:01
29-Mar-2008 05:01
mt_rand() is not faster than rand() !
Tested over 100'000 iterations, with none/various/random arguments, mt_rand is always 3% slower than rand().
guilhem at dublin dot ie
25-Mar-2008 02:09
25-Mar-2008 02:09
I'm sorry to say, "andrei at novanetworks dot ro"'s method seems higly unefficient to me. It's good if called few times only, but when most of the numbers have already been used, the function has to loop many times before finding an available option.
When I know I need to call most of the numbers from a range, I create a list of the numbers in the range, get a random index from this list, then return and delete the item of the list at the picked index. More memory usage if called many times, but probably less computation time on average.
andrei at novanetworks dot ro
23-Mar-2008 12:04
23-Mar-2008 12:04
Here's a simple function i've made for generateing unique random numbers. Be carefull, the function will go into an infinite loop if you request more unique numbers then the given range (ex. if you call unic(1, 5) five times it's ok, but the 6'th time it will go into an infinite loop).
$unic_arr = array(); //the array in witch the used numbers are stored.
function unic($min, $max) {
global $unic_arr;
$rand = mt_rand($min, $max);
$tf = 1;
while(true) {
if(!in_array($rand, $unic_arr)) {
$tf = 0;
break;
}
else $rand = mt_rand($min, $max);
}
array_push($unic_arr, $rand);
return $rand;
}
//to call the function use:
unic($min, $max); //ex. unic(1000, 9999);
William Leslie
13-Feb-2008 09:24
13-Feb-2008 09:24
Do not rely on the strength of any 'home-brewed' cryptographic algorithm, such as the one posted by dmoree at coker dot edu. Algorithms such as MD5 and SHA-1 have been the subject of intense academic research and have known security properties.
While it is true that MD5 and SHA-1 are generally no longer recommended for use in new cryptosystems, there are newer algorithms such as SHA-256 that address the older algorithms' weaknesses. These newer algorithms have not received quite as much scrutiny as their older counterparts, but have still been studied much more carefully than your home-brewed algorithm, most likely.
Dmoree at coker dot edu's concern about rainbow tables is best addressed by a properly applied salting technique. Every bit of 'salt' added to a cryptographic hash effectively extends the complexity of the password and thus the size of the rainbow table needed to crack it.
Furthermore, wisely chosen password strength policies can mitigate such attacks.
dmoree at coker dot edu
29-Jan-2008 07:49
29-Jan-2008 07:49
Here is a simple encryption algorithm I made a few months ago. I was tired of MD5 because they have rainbow tables out that will crack most any MD5 pass. Along with SHA. So encryption algorithms are getting weaker all the time. So here is new one for people to try and crack. So far no one has told me they cracked it. I also use it to generate very random passwords or character segments. Below the function is the random string generator. I tested this algorithm with mt_rand over 10 million iterations without one duplicate string. So use it in good health!
<?php
// Hexi-decimal encryption function
// Returns: 64 character encrypted string
// NOTE: One-Way encryption only
function HexCrypt($string = "", $salt = ""){
if(strlen(trim($string)) == 0){
$string = " ";
}
if(strlen(trim($salt)) == 0){
$salt = " ";
}
$string = $salt.$string.$salt;
$lastchar = "";
$output = "";
$saltlength = "0x".dechex(strlen($salt));
while(strlen($output) < 64){
$firstchar = "0x".dechex(ord(substr($string, strlen($salt), 1)));
for($i = 0; $i < strlen($string); $i++){
$strlength = "0x".dechex($output+$i+3);
if(strlen($output) >= 64){
break(2);
}elseif($lastchar == ""){
$lastchar = "0x".dechex(ord(substr($string, $i, 1)));
}else{
$current = "0x".dechex(ord(substr($string, $i, 1)));
$total = ($lastchar * $current) * ($firstchar * $saltlength);
$output .= dechex($total);
$lastchar = "";
}
}
if((strlen($string)%2) == 1){
$total = ($lastchar * $firstchar) * ($firstchar * $saltlength);
$output .= dechex($total);
}
$string = $output;
$output = "";
}
if(strlen($output) != 0){
$output = substr($output, 0, 64);
}else{
$output = substr($string, 0, 64);
}
return($output);
}
// Generates an 8 character random string
$length = 8;
$string = "";
for($i = 0; $i < 32; $i++){
$string .= mt_rand(0,9);
}
$start = mt_rand(0, (64-$length));
$salt = substr($string, mt_rand(0,20), 12);
echo "Random String: ".substr(HexCrypt($string, $salt), $start, $length)."\n";
?>
przemek at sobstel dot org
16-Jan-2008 11:00
16-Jan-2008 11:00
note that OWASP's "Guide to Cryptography" says that a Mersenne Twister (that is used by mt_rand()) "is nowhere near as good as CryptoAPI’s secure random number generation options, OpenSSL, or /dev/urandom which is available on many Unix variants. mt_rand() has been noted to produce the same number on some platforms."
remember that rand() is even weaker.
jfkallen at hotmail dot com
24-Dec-2007 03:37
24-Dec-2007 03:37
mt_rand does not seem to truly generate random numbers. Im not sure exactly which of the following is more accurate as I was applying the following to sock price deviations which do not follow normal distributions (exactly at least).
If you group observations in 11 buckets such that each bucket represents 10 percentiles and run mt_rand(0,10) 100 times you would expect a simlar result as if you ran 100 iterations of mt_rand(0,100) where each bucket represents 1 1 percentile range.
FYI I think things work slightly better as the range of mt_rand increases.
#$data is a numerical (not associative) array of numbers
sort($data);
$data_size = count($data);
#num_groups is the number of buckets
$num_groups = min($num_groups,$data_size);
$ile_size = $data_size / $num_groups;
//following creates the buckets
$groups[] = $data[0];
for ($i=1;$i<$num_groups;$i++){
$x = $i * $ile_size;
$i1 = floor($x);
$i2 = ceil($x);
$d1 = $data[$i1];
$d2 = $data[$i2];
$var = 1 - ($x-$i1);
$groups[] = ($d1 * $var) + ($d2 * (1-$var));
}
$groups[] = $data[$data_size-1];
//RUN The Random number generator
$value = array();
for ($j=0;$j<$depth;$j++){
$t = mt_rand($lower_limit,$upper_limit);
$value[] = $this->m_groups[$t];
}
//The end result is that as the number of groupas increase the accuracy (ie turue randomness seems to increase proportionally more (up to point). This is not the way it should work in nature.
root at mantoru dot de
25-Nov-2007 06:47
25-Nov-2007 06:47
I needed a function that returns true with a probability of n%, so here's what I came up with:
<?php
function probability($chance, $out_of = 100) {
$random = mt_rand(1, $out_of);
return $random <= $chance;
}
?>
A few usage examples:
<?php
/* 50% chance, equal to (bool)mt_rand(0, 1) */
var_dump(probability(50));
/* 0.1% chance, floats will not work -- "1 out of 1000 cases" */
var_dump(probability(1, 1000));
/* Practical example */
if (probability(10)) {
$damage *= 1.75; // Critical hit!
}
?>
fabiovh on gmail
13-Nov-2007 06:42
13-Nov-2007 06:42
performance: for a repetitive task, it's much faster not to use the limit parameters, as shown below. just use the % operator.
$t=microtime(true);
for($i=0;$i<1000000;$i++)
mt_rand()%3;
echo microtime(true)-$t;
echo '|';
$t=microtime(true);
for($i=0;$i<1000000;$i++)
mt_rand(0,2);
echo microtime(true)-$t;
echo '|';
$t=microtime(true);
for($i=0;$i<1000000;$i++)
mt_rand();
echo microtime(true)-$t;
output: 0.316797971725|0.442242145538|0.253082036972
bradpeabody at scientology dot net
03-Oct-2007 02:49
03-Oct-2007 02:49
[Editorial note: This suggested "security" improvement simply punts the issue to the operating system: there is no guarantee that the operating system will work any better than the Mersenne twister (although it may have more entropy available)]
If you want some random text that is more secure than what can get from a built in PHP method, you can simply do:
<?php
$myRandomText = shell_exec('head -c 128 < /dev/urandom');
?>
That will get around the fact that rand() and mt_rand() are a bad place to start generating something that is supposed to be cryptographically secure.
The only down sides to this that I see are:
a) Ugly
b) Slow (have to launch external processes)
c) Not portable (can't do this on Windows)
But if you can live with that, this will be much more secure than using rand() or mt_rand().
- Brad
www.mrnaz.com
24-Jul-2007 10:00
24-Jul-2007 10:00
This function uses mt_rand() to create a random string of specified length from an optionally supplied string of characters. It is good for generating passwords that only consist of alphanumeric characters or codes that must consist of a defined character space such as for barcodes. It can also be used to generate random hexadecimal numbers for things like encryption keys.
It is very fast, and allows for generation of strings of unlimited length.
<?php
function rand_string($len, $chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789')
{
$string = '';
for ($i = 0; $i < $len; $i++)
{
$pos = rand(0, strlen($chars)-1);
$string .= $chars{$pos};
}
return $string;
}
?>
rok dot kralj at gmail dot com
16-Jun-2007 12:42
16-Jun-2007 12:42
mt_rand function returns just a whole numbers. If you want a random float, then here's an elegant way:
<?php
function random_float ($min,$max) {
return ($min+lcg_value()*(abs($max-$min)));
}
?>
Paul Nolasco
09-May-2007 12:45
09-May-2007 12:45
Here's a more user friendly password generator. You want to make it easier for the user to enter the new password.
Output:
- First character is capitalize
- Rest of the characters are either number or letters (lowercase)
You can change the probability depending on your taste. Also by default it generates a 8-character long password.
<?php
function genPassword($length=8)
{
# first character is capitalize
$pass = chr(mt_rand(65,90)); // A-Z
# rest are either 0-9 or a-z
for($k=0; $k < $length - 1; $k++)
{
$probab = mt_rand(1,10);
if($probab <= 8) // a-z probability is 80%
$pass .= chr(mt_rand(97,122));
else // 0-9 probability is 20%
$pass .= chr(mt_rand(48, 57));
}
return $pass;
}
?>
Jonathan at jooped dot co dot uk
05-May-2007 08:04
05-May-2007 08:04
An easier password generator than earlsinclair2001.
function easyPassGen($length=10){
$enc = sh1(mt_rand().mt_rand().mt_rand());
$password = sub_str($enc, 1, $length);
return $password;
}
Might help someone (pretty simple though).
earlsinclair2001 at yahoo dot com
11-Apr-2007 10:46
11-Apr-2007 10:46
Here's my shot at writing a secure password generator function:
<?php
function passwordgenerator()
{
$password = "";
$loop = 0;
while ($loop < 12)
{
$randomchar = chr(mt_rand(35, 126));
if (!strstr($password, $randomchar))
{
$password .= $randomchar;
$loop++;
}
}
return $password;
}
chagenbu at php dot net
21-Mar-2007 10:18
21-Mar-2007 10:18
The algorithm used by mt_rand() changed in PHP 5.2.1. If you are relying on getting the same sequence from mt_rand() after calling mt_srand() with a known seed, upgrading to PHP 5.2.1 will break your code. See http://bugs.php.net/bug.php?id=40724 for something of an explanation; there is no workaround.
12-Mar-2007 01:36
In one of my forums was a discussion about, how to change an image randomly, so i wrote this code using mt_rand ....
I hope you can use it ....
I Forgot something, sorry for that, but here is the correction.
<?php
//ImageChange.php
error_reporting(0);//hide the notice for the missing $iRand
$sPath2ImageDir = Path;//preventing redundancy
$aImages = scandir($sBildOrdnerPfad);//Dir 2 Array
$iImageCount = count($aImages);//preventing redundancy
while (getimagesize("{sPath2ImageDir}/{$aImages[$iRand]}")) {//recursion to get an image
$iRand = mt_rand(2, $iImageCount-1);//min = 2 because $aImages[0] = "." and $aImages[1] = ".."
}
echo "<img alt=\"Image{$iRand}\" src=\"{sPath2ImageDir}/{$aImages[$iRand]}\" title=\"Image{$iRand}\" />";//show the image
unset($aImages, $iImageCount, $iRand, $sBildOrdnerPfad);//if this script is used in another script
?>
Rene at mokiba dot de
10-Mar-2007 02:00
10-Mar-2007 02:00
Here is my Function to generate an Array with unique random Numbers between "$from" and "$to".
<?php
function random_number_array($count, $from, $to){
for($i=$from;$i<$to;$i++){
$number_array[] = $i;
}
$random_number_array = array();
mt_srand ((double) microtime() * 1000000);
for($i=0;$i<$count;$i++){
$random_number = mt_rand(0,count($number_array)-1);
$key_to_insert_and_delete = array_search($random_number, $number_array);
$random_number_array[$i] = $number_array[$key_to_insert_and_delete];
array_splice($number_array, $key_to_insert_and_delete, 1);
}
// Array $random_number_array with $count random Numbers, between $from and $to
return $random_number_array;
}
?>
I hope its helping you.
Greetings
Rene Andris
Rene at mokiba dot de
10-Mar-2007 11:50
10-Mar-2007 11:50
Here is my Function to generate an Array with unique random Numbers between "$from" and "$to".
function random_number_array($count, $from, $to){
for($i=$from;$i<$to;$i++){
$number_array[] = $i;
}
$random_number_array = array();
mt_srand ((double) microtime() * 1000000);
for($i=0;$i<$count;$i++){
$random_number = mt_rand(0,count($number_array)-1);
$key_to_insert_and_delete = array_search($random_number, $number_array);
$random_number_array[$i] = $number_array[$key_to_insert_and_delete];
array_splice($number_array, $key_to_insert_and_delete, 1);
}
// Array $random_number_array with $count random Numbers, between $from and $to
return $random_number_array;
}
I hope its helping you.
Greetings
Rene Andris
heavyraptor
14-Feb-2007 03:26
14-Feb-2007 03:26
since my mt_rand_n() function isn't too fast I created a faster and easier function:
<?php
function mt_rand_exclusive($min,$max,$ex) {
while (true) {
if (!in_array($rand = mt_rand($min,$max),(array)$ex))
return $rand;
}
}
?>
Have fun
zolaar at nothanks dot com
07-Feb-2007 10:44
07-Feb-2007 10:44
a better (and likely faster) way to generate a random 6-digit hex string:
<?php
$num = mt_rand ( 0, 0xffffff ); // trust the library, love the library...
$output = sprintf ( "%06x" , $num ); // muchas smoochas to you, PHP!
return $output;
?>
The mt_rand function won't give you a number outside the bounds you asked for -- no need to and-off the top bits -- and the sprintf function has params for length-padding & hexidecimal output. It's likely faster because most of the work is being done by the wicked fast C functions that PHP sits on top of, though YMMV in that dept.
heavyraptor
12-Dec-2006 09:47
12-Dec-2006 09:47
If you need a random number but not the numbers in a specified array, you may use my function below:
<?php
function mt_rand_n($min,$max,$disallowed) {
// $a must be an array
if (!is_array($disallowed))
return false;
// Create an array with the numbers from $min to $max
// without the numbers in $disallowed.
// - range() to create an array with the numbers from $min to $max
// - array_diff() to create the allowed numbers
// - since array_diff() doesn't change the keys, we've to change them with
// array_values(), to get an normal order (0,1,2,3 ... )
$numbers = array_values(array_diff(range($min,$max),$disallowed));
// size of $numbers must be greater than 0
if (count($numbers) < 1)
return false;
// create random number and return it
return $numbers[mt_rand(0,count($numbers) - 1)];
}
// Example:
$min = 0;
$max = 10;
$disallowed = array(0,1,2,3,4,9,10); // the numbers 1,2,3,6,7, and 8 are disallowed
for ($i = 0; $i < 100; $i++)
var_dump(mt_rand_n($min,$max,$disallowed));
?>
I hope it helps someone ...
Btw. here's the "un-comment" function:
<?php
function mt_rand_n($min,$max,$disallowed) {
if (!is_array($disallowed)) return false;
$numbers = array_values(array_diff(range($min,$max),$disallowed));
if (count($numbers) < 1) return false;
return $numbers[mt_rand(0,count($numbers) - 1)];
}
?>
Have fun :)
MagicalTux at ooKoo dot org
20-Nov-2006 07:34
20-Nov-2006 07:34
In answer to David and pHp_n00b, about generating a random 6 characters hexadecimal string...
Well, the easiest solution would be :
<?php
$rand = mt_rand(0x000000, 0xffffff); // generate a random number between 0 and 0xffffff
$rand = dechex($rand & 0xffffff); // make sure we're not over 0xffffff, which shouldn't happen anyway
$rand = str_pad($rand, 6, '0', STR_PAD_LEFT); // add zeroes in front of the generated string
echo $rand;
?>
Some examples of generated stuff :
8514d2
3188ae
028f3e
444397
1de508
071662
You can easily make a function from this code.
Chris
10-Nov-2006 11:35
10-Nov-2006 11:35
>Running the output of Mersenne Twister through an unkeyed >secure hash is NOT a good way to make it secure, because it'll >still have a relatively small internal state which, if recovered, >would allow reproduction of the keystream. A better idea >would be to encrypt the output with a keyed encryption >algorithm - but if you were going to do that, you wouldn't >need a psuedorandom number generator at all, because a >counter would be just as good.
Not true. Mersenne Twister has an ENORMOUS amount of internal state - 4992 bits, bigger than practically any cipher's key length. The point of a secure random number generator is that you cannot predict future outputs based on past OUTPUTS, which is why a hash is applied. Clearly you can predict the future output of any pseudorandom number generator if you can acquire the internal state - a better algorithm will never solve this problem. If you use keyed encryption, recovering the key allows you to predict future outputs.
David
06-Nov-2006 12:40
06-Nov-2006 12:40
Shouldn't it be a greater than (>) sign rather than a not equal (!=) sign? Because you're just checking to see if it is exactly six. So if it is 7 it, won't try to fix it. So wouldn't this be better?
<?
//....
if (strlen($random_hex) < "6") // sometimes it returns an only 5, or less, char Hex-Code,
hexcode(); // so the function has to be repeat
elseif (strlen($random_hex) > "6") // sometimes it returns 7 or more characters
//...I don't know how to make it do only six, but your code seems to only check to make sure it doesn't do less than 6; nothing to counter doing more than 6.... so here would be some code to reduce the size back to 6 if it went over.
else
echo $random_hex; // returns the Hex-Code
}
//...
?>
pHp_n00b
26-Sep-2006 07:00
26-Sep-2006 07:00
<?php
// Generates a max."6 char" Hex-Code
function hexcode()
{
$min = hexdec("000000"); // result is 0 and sets the min-value for mt_rand
$max = hexdec("FFFFFF"); // result is 16777215 and sets the max-value for mt_rand
$random = mt_rand($min, $max); // creates a radom number between 0 and 16777215
$random_hex = dechex($random); // transforms the random number into a Hex-Code
// now the test, if the result has 6 chars
if (strlen($random_hex) != "6") // sometimes it returns an only 5, or less, char Hex-Code,
hexcode(); // so the function has to be repeat
else
echo $random_hex; // returns the Hex-Code
}
hexcode();
?>
MagicalTux at ooKoo dot org
25-Aug-2006 05:44
25-Aug-2006 05:44
Since many people wrote little scripts to generate random sequences, I'll also give mine (which is slightly faster since it makes use of strlen only once, and uses strings instead of arrays) :
<?php
function code($nc, $a='abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789') {
$l=strlen($a)-1; $r='';
while($nc-->0) $r.=$a{mt_rand(0,$l)};
return $r;
}
?>
arias at elleondeoro dot com
29-May-2006 02:03
29-May-2006 02:03
Be carefull with: $characters[mt_rand(0, count($characters))];
"If you want a random number between 5 and 15 (inclusive), for example, use mt_rand (5, 15)."
Array index are between 0 and n-1, but mt_rand generates a number between 0 and n!
James
15-Apr-2006 11:02
15-Apr-2006 11:02
The Developers Resources article mentioned above should be removed as that site has be down for years. The same article by Gregory Boshoff is available at http://www.phpfive.net/article2.htm
rollerce at gmail dot com
15-Feb-2006 05:38
15-Feb-2006 05:38
I know a bunch of you have posted little snippets for random number generation, but here's a nifty (in my opinion) little thing I just wrote to create a 10 digit code with hyphens in it. It also negates the use of 0, O, 1, and I, to avoid confusion. I am ALWAYS willing to accept input so if any of you has suggestions to streamline the code, please let me know.
<?php
function GetID($x){
$characters = array("A", "B", "C", "D", "E", "F", "G", "H", "J", "K", "L", "M", "N", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z", "2", "3", "4", "5", "6", "7", "8", "9");
shuffle($characters);
for (; strlen($ReqID)<$x;){
$ReqID .= $characters[mt_rand(0, count($characters))];
}
return $ReqID;
}
$ReqID .= GetID(3);
$ReqID .= "-";
$ReqID .= GetID(4);
$ReqID .= "-";
$ReqID .= GetID(3);
echo $ReqID
?>
ripat at lumadis dot be
07-Nov-2005 08:38
07-Nov-2005 08:38
Yet another snippet to generate a password.
<?php
$acceptedChars = 'azertyuiopqsdfghjklmwxcvbnAZERTYUIOPQSDFGHJKLMWXCVBN0123456789';
$max = strlen($acceptedChars)-1;
$password = null;
for($i=0; $i < 8; $i++) {
$password .= $acceptedChars{mt_rand(0, $max)};
}
echo $password;
?>
I have tried several ways of doing it but this simple one seems to be the fastest.
fahri at konse dot de
08-Oct-2005 09:12
08-Oct-2005 09:12
i did the following, to generate a few random-numbers out of a total amount of numbers, but to create different random-numbers and not double or tripple.
for example i use it to generate 10 random-pics out of 150, and do shurely generate not twice the same...
<?php
$total = 6; // available numbers (of pictures)
$randanzahl = 6; //number of random-number to generate out of $total
function checkifdouble($ran,$i) {
for($j=1; $j<$i; $j++) {
if($ran[$j]==$ran[$i]) {
$ergebnis="true";
break;
} //endif
else {
$ergebnis="false";
} //endelse
} //endfor
return $ergebnis;
}
for ($i=1; $i<=$randanzahl; $i++) {
$ran[$i] = mt_rand(1, $total);
if ($i>1) {
while(checkifdouble($ran,$i)=="true") {
$ran[$i] = mt_rand(1, $total);
$v=checkifdouble($ran,$i);
echo($v);
} //endif
}
echo($ran[$i]."<br>");
} //enfor
?>
this version is easily for debugging and adaption!
maybe there is a very shorter version...
phil [underscore] ozil at hotmail dot com
07-Oct-2005 06:13
07-Oct-2005 06:13
Quit bothering yourselves.
All it takes to create a secure random-generated password is those three lines:
<?php
$pass = "";
// Generate a 8 char password
for ($i=0; $i<8; $i++)
$pass .= chr(mt_rand(35, 126));
?>
Note:
In this example, the character's ASCII values range from 35 to 126.
For character's ASCII codes please check:
http://www.keller.com/html-quickref/latin1.html
frans-jan at van-steenbeek dot net
03-Oct-2005 07:18
03-Oct-2005 07:18
My try at generating a reasonably secure password:
<?php
function keygen() {
$tempstring =
"0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNO
PQRSTUVWXYZ0123456789abcdefghijklmnopqrstuvwxyzABC
DEFGHIJKLMNOPQRSTUVWXYZ!?@#$%&*[]{}();:,<>~+=-_
/|\\";
for($length = 0; $length < mt_rand(10, 15); $length++) {
$temp = str_shuffle($tempstring);
$char = mt_rand(0, strlen($temp));
$pass .= $temp[$char];
}
return $pass;
}
echo(keygen());
echo("\n");
?>
This generates a password of an undefined length (in this case, 10 to 15 chars) consisting of numbers, UPPERCASE letters lowercase letters and a set of signs. I have doubled the chance of number and letters to reduce the confusion with my users.
sean at codeaholics dot com
22-Jul-2005 06:31
22-Jul-2005 06:31
You really shouldn't generate a number to determine the _type_ of the char, then the char itself. If security is an issue for you, and you want to maintain as much entropy as possible, you should use a function similar to the one below. Since this seems to be getting repeated over-and-over, I explained (beat into the ground?) the issue on http://www.codeaholics.com/randomCode.php
The code:
<?php
////
// Returns a random code of the specified length, containing characters that are
// equally likely to be any of the digits, uppercase letters, or lowercase letters.
//
// The default length of 10 provides 839299365868340224 (62^10) possible codes.
//
// NOTE: Do not call wt_srand(). It is handled automatically in PHP 4.2.0 and above
// and any additional calls are likely to DECREASE the randomness.
////
function randomCode($length=10){
$retVal = "";
while(strlen($retVal) < $length){
$nextChar = mt_rand(0, 61); // 10 digits + 26 uppercase + 26 lowercase = 62 chars
if(($nextChar >=10) && ($nextChar < 36)){ // uppercase letters
$nextChar -= 10; // bases the number at 0 instead of 10
$nextChar = chr($nextChar + 65); // ord('A') == 65
} else if($nextChar >= 36){ // lowercase letters
$nextChar -= 36; // bases the number at 0 instead of 36
$nextChar = chr($nextChar + 97); // ord('a') == 97
} else { // 0-9
$nextChar = chr($nextChar + 48); // ord('0') == 48
}
$retVal .= $nextChar;
}
return $retVal;
}
?>
mina86 at nospam dot projektcode dot org
24-May-2005 05:00
24-May-2005 05:00
Re: solenoid at hotmail dot united dot kingdom
In theory method shown by selenoid can lead to infinite loop. The correct method would be:
<?php
$randomNumbers = array();
for ($i = 0; i<30; ++$i) $randomNumbers[] = $i;
shuffle($randomNumbers);
for ($i = 20; $i<30; ++$i) unset($randomNumbers[$i]);
$randomNumbers = array_values($randomNumbers);
?>
The last two lines may be in some cases removed.
nowhere at where dot net
16-Apr-2005 02:46
16-Apr-2005 02:46
Allows characters 0-9, a-z
Weighted (and tested) ok.
<?php
function generate_string ($length = 20)
{
$nps = "";
for($i=0;$i<$length;$i++)
{
$nps .= chr( (mt_rand(1, 36) <= 26) ? mt_rand(97, 122) : mt_rand(48, 57 ));
}
return $nps;
}
?>
mskala at ansuz dot sooke dot bc dot ca
23-Jan-2005 03:47
23-Jan-2005 03:47
Running the output of Mersenne Twister through an unkeyed secure hash is NOT a good way to make it secure, because it'll still have a relatively small internal state which, if recovered, would allow reproduction of the keystream. A better idea would be to encrypt the output with a keyed encryption algorithm - but if you were going to do that, you wouldn't need a psuedorandom number generator at all, because a counter would be just as good.
timr at onlinehome dot de
12-Aug-2004 04:24
12-Aug-2004 04:24
The correct address of the inventor's FAQ is (http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/efaq.html). They state that Mersenne Twister may be used for cryptography if you do some post-processing:
"Mersenne Twister is not cryptographically secure. (MT is based on a linear recursion. Any pseudorandom number sequence generated by a linear recursion is insecure, since from sufficiently long subsequence of the outputs, one can predict the rest of the outputs.)
To make it secure, you need to use some Secure Hashing Algorithm with MT. For example, you may gather every eight words of outputs, and compress them into one word (thus the length of the output sequence is 1/8 of the original one)."
11-Feb-2004 05:27
Here is a example of a very small, compact, quite random-random string generator. It will make a string with uppercase & lowercase letters, with numbers. You simply need to set $len in the for() structure, and then the string will be in $r. It has been designed for size, while it's still quite fast. Mind the wrapping, it should be 1 line.
<?php
for($len=8,$r='';strlen($r)<$len;$r.=chr(!mt_rand(0,2)?
mt_rand(48,57):(!mt_rand(0,1)?mt_rand(65,90):mt_rand
(97,122))));
?>
Armond Carroll
tmx at ntlworld dot com
06-Dec-2003 01:26
06-Dec-2003 01:26
When using this function, it doesn't matter which order the numbers go in.
mt_rand(16,5)
works just as well as
mt_rand(5,16)
Which can be useful if you are pulling values from a database, that could be negative or positive.
mtrand(0,$anyinteger)
Hope this helps someone
daeken_9999 at yahoo dot com
08-Jul-2003 02:44
08-Jul-2003 02:44
This is a fixed version of the gaussrand() function defined in a note above.
<?php
function gaussrand()
{
static $V2, $V1, $S;
static $phase = 0;
if (phase == 0)
{
while ($S >= 1 || $S == 0)
{
$V1 = 2 * (rand() / getrandmax()) - 1;
$V2 = 2 * (rand() / getrandmax()) - 1;
$S = $V1 * $V1 + $V2 * $V2;
}
$X = $V1 * sqrt(-2 * log($S) / $S);
}
else
$X = $V2 * sqrt(-2 * log($S) / $S);
$phase = 1 - $phase;
return $X;
}
?>
js