Generating Random, Unique Alphanumeric Strings

In various applications, such as account verification links, it's crucial to generate unique and random strings consisting of numbers and letters. Here's how you can achieve this in PHP:

PHP 7

PHP 7 introduces the random_bytes($length) function to provide cryptographically secure pseudo-random bytes. An example:

$bytes = random_bytes(20);
var_dump(bin2hex($bytes));

This will produce an output like:

string(40) "5fe69c95ed70a9869d9f9af7d8400a6673bb9ce9"

PHP 5 (Outdated)

For PHP 5, it's recommended to utilize openssl_random_pseudo_bytes() instead, which generates cryptographically secure tokens. A simple solution:

bin2hex(openssl_random_pseudo_bytes($bytes))

More Secure Approach

To enhance security, the following function can generate a random, unique alphanumeric string within a specified length range:

function getToken($length)
{
    $codeAlphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
    $max = strlen($codeAlphabet); // edited

    for ($i=0; $i < $length; $i  ) {
        $token .= $codeAlphabet[crypto_rand_secure(0, $max-1)];
    }

    return $token;
}

This approach incorporates crypto_rand_secure($min, $max) as a drop-in replacement for rand() or mt_rand(), utilizing openssl_random_pseudo_bytes to guarantee randomness.