I'm trying to create a randomized string in PHP, and I get absolutely no output with this:
<?php
function RandomString()
{
$characters = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
$randstring = '';
for ($i = 0; $i < 10; $i++) {
$randstring = $characters[rand(0, strlen($characters))];
}
return $randstring;
}
RandomString();
echo $randstring;
What am I doing wrong?
To answer this question specifically, two problems:
$randstring is not in scope when you echo it.
The characters are not getting concatenated together in the loop.
Here's a code snippet with the corrections:
function generateRandomString($length = 10) {
$characters = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
$charactersLength = strlen($characters);
$randomString = '';
for ($i = 0; $i < $length; $i++) {
$randomString .= $characters[random_int(0, $charactersLength - 1)];
}
return $randomString;
}
Output the random string with the call below:
// Echo the random string.
// Optionally, you can give it a desired string length.
echo generateRandomString();
Please note that previous version of this answer used rand() instead of random_int() and therefore generated predictable random strings. So it was changed to be more secure, following advice from this answer.
Note: str_shuffle() internally uses rand(), which is unsuitable for cryptography purposes (e.g. generating random passwords). You want a secure random number generator instead. It also doesn't allow characters to repeat.
One more way.
UPDATED (now this generates any length of string):
function generateRandomString($length = 10) {
return substr(str_shuffle(str_repeat($x='0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ', ceil($length/strlen($x)) )),1,$length);
}
echo generateRandomString(); // OR: generateRandomString(24)
That's it. :)
There are a lot of answers to this question, but none of them leverage a Cryptographically Secure Pseudo-Random Number Generator (CSPRNG).
The simple, secure, and correct answer is to use RandomLib and don't reinvent the wheel.
For those of you who insist on inventing your own solution, PHP 7.0.0 will provide random_int() for this purpose; if you're still on PHP 5.x, we wrote a PHP 5 polyfill for random_int() so you can use the new API even before you upgrade to PHP 7.
Safely generating random integers in PHP isn't a trivial task. You should always check with your resident StackExchange cryptography experts before you deploy a home-grown algorithm in production.
With a secure integer generator in place, generating a random string with a CSPRNG is a walk in the park.
Creating a Secure, Random String
/**
* Generate a random string, using a cryptographically secure
* pseudorandom number generator (random_int)
*
* This function uses type hints now (PHP 7+ only), but it was originally
* written for PHP 5 as well.
*
* For PHP 7, random_int is a PHP core function
* For PHP 5.x, depends on https://github.com/paragonie/random_compat
*
* #param int $length How many characters do we want?
* #param string $keyspace A string of all possible characters
* to select from
* #return string
*/
function random_str(
int $length = 64,
string $keyspace = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'
): string {
if ($length < 1) {
throw new \RangeException("Length must be a positive integer");
}
$pieces = [];
$max = mb_strlen($keyspace, '8bit') - 1;
for ($i = 0; $i < $length; ++$i) {
$pieces []= $keyspace[random_int(0, $max)];
}
return implode('', $pieces);
}
Usage:
$a = random_str(32);
$b = random_str(8, 'abcdefghijklmnopqrstuvwxyz');
$c = random_str();
Demo: https://3v4l.org/IMJGF (Ignore the PHP 5 failures; it needs random_compat)
This creates a 20 character long hexadecimal string:
$string = bin2hex(openssl_random_pseudo_bytes(10)); // 20 chars
In PHP 7 (random_bytes()):
$string = base64_encode(random_bytes(10)); // ~14 characters, includes /=+
// or
$string = substr(str_replace(['+', '/', '='], '', base64_encode(random_bytes(32))), 0, 32); // 32 characters, without /=+
// or
$string = bin2hex(random_bytes(10)); // 20 characters, only 0-9a-f
#tasmaniski: your answer worked for me. I had the same problem, and I would suggest it for those who are ever looking for the same answer. Here it is from #tasmaniski:
<?php
$random = substr(md5(mt_rand()), 0, 7);
echo $random;
?>
Here is a youtube video showing us how to create a random number
Depending on your application (I wanted to generate passwords), you could use
$string = base64_encode(openssl_random_pseudo_bytes(30));
Being base64, they may contain = or - as well as the requested characters. You could generate a longer string, then filter and trim it to remove those.
openssl_random_pseudo_bytes seems to be the recommended way way to generate a proper random number in php. Why rand doesn't use /dev/random I don't know.
PHP 7+ Generate cryptographically secure random bytes using random_bytes function.
$bytes = random_bytes(16);
echo bin2hex($bytes);
Possible output
da821217e61e33ed4b2dd96f8439056c
PHP 5.3+ Generate pseudo-random bytes using openssl_random_pseudo_bytes function.
$bytes = openssl_random_pseudo_bytes(16);
echo bin2hex($bytes);
Possible output
e2d1254506fbb6cd842cd640333214ad
The best use case could be
function getRandomBytes($length = 16)
{
if (function_exists('random_bytes')) {
$bytes = random_bytes($length / 2);
} else {
$bytes = openssl_random_pseudo_bytes($length / 2);
}
return bin2hex($bytes);
}
echo getRandomBytes();
Possible output
ba8cc342bdf91143
Here is a simple one-liner that generates a true random string without any script level looping or use of OpenSSL libraries.
echo substr(str_shuffle(str_repeat('0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ', mt_rand(1,10))), 1, 10);
To break it down so the parameters are clear
// Character List to Pick from
$chrList = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
// Minimum/Maximum times to repeat character List to seed from
$chrRepeatMin = 1; // Minimum times to repeat the seed string
$chrRepeatMax = 10; // Maximum times to repeat the seed string
// Length of Random String returned
$chrRandomLength = 10;
// The ONE LINE random command with the above variables.
echo substr(str_shuffle(str_repeat($chrList, mt_rand($chrRepeatMin,$chrRepeatMax))), 1, $chrRandomLength);
This method works by randomly repeating the character list, then shuffles the combined string, and returns the number of characters specified.
You can further randomize this, by randomizing the length of the returned string, replacing $chrRandomLength with mt_rand(8, 15) (for a random string between 8 and 15 characters).
A better way to implement this function is:
function RandomString($length) {
$keys = array_merge(range(0,9), range('a', 'z'));
$key = "";
for($i=0; $i < $length; $i++) {
$key .= $keys[mt_rand(0, count($keys) - 1)];
}
return $key;
}
echo RandomString(20);
mt_rand is more random according to this and this in PHP 7. The rand function is an alias of mt_rand.
function generateRandomString($length = 15)
{
return substr(sha1(rand()), 0, $length);
}
Tada!
$randstring in the function scope is not the same as the scope where you call it. You have to assign the return value to a variable.
$randstring = RandomString();
echo $randstring;
Or just directly echo the return value:
echo RandomString();
Also, in your function you have a little mistake. Within the for loop, you need to use .= so each character gets appended to the string. By using = you are overwriting it with each new character instead of appending.
$randstring .= $characters[rand(0, strlen($characters))];
First, you define the alphabet you want to use:
$alphanum = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
$special = '~!##$%^&*(){}[],./?';
$alphabet = $alphanum . $special;
Then, use openssl_random_pseudo_bytes() to generate proper random data:
$len = 12; // length of password
$random = openssl_random_pseudo_bytes($len);
Finally, you use this random data to create the password. Because each character in $random can be chr(0) until chr(255), the code uses the remainder after division of its ordinal value with $alphabet_length to make sure only characters from the alphabet are picked (note that doing so biases the randomness):
$alphabet_length = strlen($alphabet);
$password = '';
for ($i = 0; $i < $len; ++$i) {
$password .= $alphabet[ord($random[$i]) % $alphabet_length];
}
Alternatively, and generally better, is to use RandomLib and SecurityLib:
use SecurityLib\Strength;
$factory = new RandomLib\Factory;
$generator = $factory->getGenerator(new Strength(Strength::MEDIUM));
$password = $generator->generateString(12, $alphabet);
I've tested performance of most popular functions there, the time which is needed to generate 1'000'000 strings of 32 symbols on my box is:
2.5 $s = substr(str_shuffle(str_repeat($x='0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ', ceil($length/strlen($x)) )),1,32);
1.9 $s = base64_encode(openssl_random_pseudo_bytes(24));
1.68 $s = bin2hex(openssl_random_pseudo_bytes(16));
0.63 $s = base64_encode(random_bytes(24));
0.62 $s = bin2hex(random_bytes(16));
0.37 $s = substr(md5(rand()), 0, 32);
0.37 $s = substr(md5(mt_rand()), 0, 32);
Please note it is not important how long it really was but which is slower and which one is faster so you can select according to your requirements including cryptography-readiness etc.
substr() around MD5 was added for sake of accuracy if you need string which is shorter than 32 symbols.
For sake of answer: the string was not concatenated but overwritten and result of the function was not stored.
Here's my simple one line solution to generate a use friendly random password, excluding the characters that lookalike such as "1" and "l", "O" and "0", etc... here it is 5 characters but you can easily change it of course:
$user_password = substr(str_shuffle('abcdefghjkmnpqrstuvwxyzABCDEFGHJKMNPQRSTUVWXYZ23456789'),0,5);
One very quick way is to do something like:
substr(md5(rand()),0,10);
This will generate a random string with the length of 10 chars. Of course, some might say it's a bit more heavy on the computation side, but nowadays processors are optimized to run md5 or sha256 algorithm very quickly. And of course, if the rand() function returns the same value, the result will be the same, having a 1 / 32767 chance of being the same. If security's the issue, then just change rand() to mt_rand()
function gen_uid($l=5){
return substr(str_shuffle("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"), 10, $l);
}
echo gen_uid();
Default Value[5]: WvPJz
echo gen_uid(30);
Value[30]: cAiGgtf1lDpFWoVwjykNKXxv6SC4Q2
Short Methods..
Here are some shortest method to generate the random string
<?php
echo $my_rand_strng = substr(str_shuffle("0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"), -15);
echo substr(md5(rand()), 0, 7);
echo str_shuffle(MD5(microtime()));
?>
Helper function from Laravel 5 framework
/**
* Generate a "random" alpha-numeric string.
*
* Should not be considered sufficient for cryptography, etc.
*
* #param int $length
* #return string
*/
function str_random($length = 16)
{
$pool = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
return substr(str_shuffle(str_repeat($pool, $length)), 0, $length);
}
Since php7, there is the random_bytes functions.
https://www.php.net/manual/ru/function.random-bytes.php
So you can generate a random string like that
<?php
$bytes = random_bytes(5);
var_dump(bin2hex($bytes));
?>
from the yii2 framework
/**
* Generates a random string of specified length.
* The string generated matches [A-Za-z0-9_-]+ and is transparent to URL-encoding.
*
* #param int $length the length of the key in characters
* #return string the generated random key
*/
function generateRandomString($length = 10) {
$bytes = random_bytes($length);
return substr(strtr(base64_encode($bytes), '+/', '-_'), 0, $length);
}
function rndStr($len = 64) {
$randomData = file_get_contents('/dev/urandom', false, null, 0, $len) . uniqid(mt_rand(), true);
$str = substr(str_replace(array('/','=','+'),'', base64_encode($randomData)),0,$len);
return $str;
}
This one was taken from adminer sources:
/** Get a random string
* #return string 32 hexadecimal characters
*/
function rand_string() {
return md5(uniqid(mt_rand(), true));
}
Adminer, database management tool written in PHP.
/**
* #param int $length
* #param string $abc
* #return string
*/
function generateRandomString($length = 10, $abc = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ")
{
return substr(str_shuffle($abc), 0, $length);
}
Source from http://www.xeweb.net/2011/02/11/generate-a-random-string-a-z-0-9-in-php/
Another one-liner, which generates a random string of 10 characters with letters and numbers. It will create an array with range (adjust the second parameter to set the size), loops over this array and assigns a random ASCII character (range 0-9 or a-z), then implodes the array to get a string.
$str = implode('', array_map(function () { return chr(rand(0, 1) ? rand(48, 57) : rand(97, 122)); }, range(0, 9)));
Note: this only works in PHP 5.3 and later
One liner.
It is fast for huge strings with some uniqueness.
function random_string($length){
return substr(str_repeat(md5(rand()), ceil($length/32)), 0, $length);
}
function randomString($length = 5) {
return substr(str_shuffle(implode(array_merge(range('A','Z'), range('a','z'), range(0,9)))), 0, $length);
}
Here is how I am doing it to get a true unique random key:
$Length = 10;
$RandomString = substr(str_shuffle(md5(time())), 0, $Length);
echo $RandomString;
You can use time() since it is a Unix timestamp and is always unique compared to other random mentioned above. You can then generate the md5sum of that and take the desired length you need from the generated MD5 string. In this case I am using 10 characters, and I could use a longer string if I would want to make it more unique.
I hope this helps.
The edited version of the function works fine, but there is just one issue I found: You used the wrong character to enclose $characters, so the ’ character is sometimes part of the random string that is generated.
To fix this, change:
$characters = ’0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ’;
to:
$characters = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
This way only the enclosed characters are used, and the ’ character will never be a part of the random string that is generated.
function generateRandomString($length = 10, $hasNumber = true, $hasLowercase = true, $hasUppercase = true): string
{
$string = '';
if ($hasNumber)
$string .= '0123456789';
if ($hasLowercase)
$string .= 'abcdefghijklmnopqrstuvwxyz';
if ($hasUppercase)
$string .= 'ABCDEFGHIJKLMNOPQRSTUVWXYZ';
return substr(str_shuffle(str_repeat($x = $string, ceil($length / strlen($x)))), 1, $length);
}
and use:
echo generateRandomString(32);
I liked the last comment which used openssl_random_pseudo_bytes, but it wasn't a solution for me as I still had to remove the characters I didn't want, and I wasn't able to get a set length string. Here is my solution...
function rndStr($len = 20) {
$rnd='';
for($i=0;$i<$len;$i++) {
do {
$byte = openssl_random_pseudo_bytes(1);
$asc = chr(base_convert(substr(bin2hex($byte),0,2),16,10));
} while(!ctype_alnum($asc));
$rnd .= $asc;
}
return $rnd;
}
I would like to create a random ID like an airline ticket with out any zeros, o's, ones's, or L's. It would be nice if server time was used in the generation process so no two IDs will be the same. How would one do this?
Following the awesome PHP naming scheme:
function generate_airline_ticket_number($length) {
$characters = '23456789abcdefghjkmnpqrstuvwxyzABCDEFGHJKMNPQRSTUVWXYZ';
$max = strlen($characters) - 1;
$string = '';
for ($i = 0; $i < $length; $i++) {
$string .= $characters[mt_rand(0, $max)];
}
return $string;
}
I should submit this to be included into PHP6 ;)
If you're worried about collisions, my approach would be to do an endless loop:
do
{
$random_stuff = generate_airline_ticket_number(10);
} while(check_if_string__is_not_in__the_database($random_stuff));
There is always possibility that generated number will be repeated.
You have to store that generated earlier numbers and always check if currently generated number does not exist.
To generate a random number you can just use int rand ( int $min , int $max )
uniqid() seems perfect, apart from your limitations on letters and numbers. Selecting a great font may mitigate some of your needs, so you have L, a zero with a strike through, etc.
Baring that, you haven't placed any other limitations so what about.
$id = uniqid()
$bad = array("0", "o", "l", "1");
$good = array("-", "#", "&", "$");
$id_clean = str_replace($bad, $good, $id);
The power of uniqid() combined with easily identified characters.
Another option
function genGoodRandString() {
$rnd_id = md5(uniqid(rand(), true)); // get long random id
$bad = array('0','o','1','l','8'); // define bad chars
$fixed = str_replace($bad, '', $rnd_id); // fix
return substr($fixed, 0, 10); // cut to required length
}
Why not just use a hash like MD5? I believe PHP has a md5() function built in. Another good one to use is sha1().
Using both of these hash functions you will end up getting what you don't want so I suggest you run a regex pattern on the hash to replace them with a random letter A-Z.
Oh, and hashes are usually 100% unique.
I guess I learned something new today.
I need PHP function that will create 8 chars long [a-z] hash from any input string.
So e.g. when I'll submit "Stack Overflow" it will return e.g. "gdqreaxc" (8 chars [a-z] no numbers allowed)
Perhaps something like:
$hash = substr(strtolower(preg_replace('/[0-9_\/]+/','',base64_encode(sha1($input)))),0,8);
This produces a SHA1 hash, base-64 encodes it (giving us the full alphabet), removes non-alpha chars, lowercases it, and truncates it.
For $input = 'yar!';:
mwinzewn
For $input = 'yar!!';:
yzzhzwjj
So the spread seems pretty good.
This function will generate a hash containing evenly distributed characters [a-z]:
function my_hash($string, $length = 8) {
// Convert to a string which may contain only characters [0-9a-p]
$hash = base_convert(md5($string), 16, 26);
// Get part of the string
$hash = substr($hash, -$length);
// In rare cases it will be too short, add zeroes
$hash = str_pad($hash, $length, '0', STR_PAD_LEFT);
// Convert character set from [0-9a-p] to [a-z]
$hash = strtr($hash, '0123456789', 'qrstuvwxyz');
return $hash;
}
By the way, if this is important for you, for 100,000 different strings you'll have ~2% chance of hash collision (for a 8 chars long hash), and for a million of strings this chance rises up to ~90%, if my math is correct.
function md5toabc($myMD5)
{
$newString = "";
for ($i = 0; $i < 16; $i+=2)
{
//add the first val of 0-15 to the second val of 0-15 for a range of 0-30
$myintval = hexdec(substr($myMD5, $i, $i +1) ) +
hexdec(substr($myMD5, $i+1, $i +2) );
// mod by 26 and add 97 to get to the lowercase ascii range
$newString .= chr(($myintval%26) + 97);
}
return $newString;
}
Note this introduces bias to various characters, but do with it what you will.
(Like when you roll two dice, the most common value is a 7 combined...) plus the modulo, etc...
one can give you a good a-p{8} (but not a-z) by using and modifying (the output of) a well known algo:
function mini_hash( $string )
{
$h = hash( 'crc32' , $string );
for($i=0;$i<8;$i++) {
$h{$i} = chr(96+hexdec($h{$i}));
}
return $h;
}
interesting set of constraints you posted there
how about
substr (preg_replace(md5($mystring), "/[1-9]/", ""), 0, 8 );
you could add a bit more entorpy by doing a
preg_replace($myString, "1", "g");
preg_replace($myString, "2", "h");
preg_replace($myString, "3", "i");
etc instead of stripping the digits.