Create unique plus random alphanumeric string

Question

in a simple user table while adding users, the primary key "userid" field is automatically unique since it increments automatically. But I want to add another alphanumeric field of maximum length of 8 char which will be unique for each user. The following is the function I used. I got it from a website.

function unique_code($limit)
{
 return substr(base_convert(sha1(uniqid(mt_rand())), 16, 36), 0, $limit);
 }
 echo unique_code(8);

Will it always give me unique value? If yes, then it's okay. But if no, is there any other way?

Will it always give me unique value? no. why because it includes sha1 and then substr of only 8 chars. Some may collide because first 8 chars are the same. — Lawrence Cherone
– Lawrence Cherone, Commented Jul 18, 2020 at 20:55

GNassro · Accepted Answer · 2020-07-18 21:14:49Z

1

as mentioned here , uniqid() can create the same id many times:

<?php
for($i=0;$i<20;$i++) {
    echo uniqid(), PHP_EOL;
}

/** Example of Output:

5819f3ad1c0ce
5819f3ad1c0ce
5819f3ad1c0ce
5819f3ad1c0ce
5819f3ad1c0ce
5819f3ad1c0ce
5819f3ad1c0ce
5819f3ad1c0ce
5819f3ad1c4b6
5819f3ad1c4b6
5819f3ad1c4b6
5819f3ad1c4b6
5819f3ad1c4b6
5819f3ad1c4b6
5819f3ad1c4b6
5819f3ad1c4b6
5819f3ad1c4b6
5819f3ad1c4b6
5819f3ad1c4b6
5819f3ad1c4b6 */

i suggest to use the function that he created instead of using uniqid().

<?php
function uniqidReal($lenght = 13) {
    // uniqid gives 13 chars, but you could adjust it to your needs.
    if (function_exists("random_bytes")) {
        $bytes = random_bytes(ceil($lenght / 2));
    } elseif (function_exists("openssl_random_pseudo_bytes")) {
        $bytes = openssl_random_pseudo_bytes(ceil($lenght / 2));
    } else {
        throw new Exception("no cryptographically secure random function available");
    }
    return substr(bin2hex($bytes), 0, $lenght);
}

edited Jul 18, 2020 at 21:14

answered Jul 18, 2020 at 21:00

GNassro

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1 Comment

Lawrence Cherone Over a year ago

uniqid has a more entropy option: 3v4l.org/iHMO6 also if done in a loop like your example then one would use the unique iteration number to add additional entropy 3v4l.org/sYan5

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