I am trying to create a function which creates a random String. This String should consist of letters (only caps) and numbers. It will be used to activate a product. So the user has to type it into a text field. So far I found the following function:
function random_str($length, $keyspace = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ'){ $pieces = []; $max = mb_strlen($keyspace, '8bit') - 1; for ($i = 0; $i < $length; ++$i) { $pieces []= $keyspace[random_int(0, $max)]; } return implode('', $pieces); }
I do not have that much experience with random functions. So is there anything to improve or would you suggest a different function?
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Answer
To generate a cryptographically secure random string (which I would recommend for an activation key), I would rather use openssl_random_pseudo_bytes
You can find the doc here and some useful informations in that thread (for example, how to get a random string with 0-9A-Z characters rather than just 0-9A-F).
As of PHP7.0 you could also use random_bytes, which is also cryptographically secure.