Generate unique random alphanumeric characters that are 7 characters long

Question

It need not be meaningful words - more like random password generation, but the catch is - they should be unique. I will be using this for some kind of package / product cod

Answer 1

Use Kohana text,

http://docs.kohanaphp.com/helpers/text

For example,

   $prod_id = text::random('alpha', 7);

If you don't want use the framework, you can simply copy the code. You will find lots of goodies there.

Answer 2

Heres a very simple way

$chars = 'abcdefghijklmnopqrstuvwxyz0123456789';
$temp_pw = substr( str_shuffle( $chars ), 0, 7 );
if ( check_unique( $temp_pw ) ) {
    $pw = $temp_pw;
}

You'll have to implement your own check_unique function. That part should be easy.

Answer 3

Here's how I would solve this problem:

Consider that the 7 characters can be one of 26 letters (abc..z), or 10 numbers (01...9). This makes 36 possible characters.

Each time your application generates a new code, have it increment a global variable. You can turn this unique number into a unique string by using a "Hexatridecimal" converter, and by adding filler characters to make up the rest of the string.

Take a look at this link. I think this guy had the same problem as you: http://www.codemaxima.com/2010/04/the-hexatridecimal-numbering-system/

Answer 4

$random = substr(hash('md5',openssl_random_pseudo_bytes(32)),0,7);

Answer 5

Given that you mention passwords here, I'll assume you need a secure method (ie: someone shouldn't be able to guess someone else's password based on knowing any other password). You could use the following:

1. Decide on a master password, for example "MasterPassword"
2. For each password generated, append to that either a random or sequential nonce, for example "MasterPassword1", "MasterPassword2".
3. Perform a cryptographic hash on that (SHA, MD5, etc) and covert the hash to a hexadecimal representation, eg "ce7f181a44a4a5b7e43fe2b9a0b1f0c1".
4. Truncate that to as many characters as you need - perhaps seven as you indicated: "ce7f181".
5. Check if that has been assigned before. If not, return that as your password. Otherwise, repeat from 2.

If security is not an issue, steps 1 and 2 by themselves would be sufficient. If security is an issue, it is vital that no one but yourself knows the value of "MasterPassword".

Answer 6

Galen's answer allows only one use of each character in the password. Not much information in that string. A simple change though:

$chars = 'abcdefghijklmnopqrstuvwxyz0123456789';
$passwordlength = 7;
for ($x = 1; $x <= $passwordlength; $x++) {
  $charlist .= $chars;
}
$temp_pw = substr( str_shuffle( $charlist ), 0, $passwordlength );