Generating confirmation code for an email confirmation

Question

Using PHP, what are some ways to generate a random confirmation code that can be stored in a DB and be used for email confirmation? I can't for the life of me think of a way to generate a unique number that can be generated from a user's profile. That way I can use a function to make the number small enough to be included in the URL (see this link). Remember, the user has to click on the link to "confirm/activate" his/her account. If I can't use numbers, I have no problems using both letters and numbers.

With that said, I've tried hashing the username along with a "salt" to generate the random code. I know there has to be a better way, so let's hear it.

Answer 1

$random_hash = md5(uniqid(rand(), true));

That will be 32 alphanumeric characters long and unique. If you want it to be shorter just use substr():

$random_hash = substr(md5(uniqid(rand(), true)), 0, 16); // 16 characters long

Answer 2

1) Create an Activated Field in Database

2) After registration the Email is sent

3) Create a Link to include in Email,Use a Unique identifier It would look something like this

Welcome Username Thanks for registering.

Please Click on the Link below to activate your account

domain.com/register.php?uid=100&activate=1

4) Update the Activated Field to true

$email_encrypt = urlencode($email);
$special_string = 'maybeyourcompanynamereversed?';
$hash = md5($email_encrypt.$special_string);

Here is the link that is sent to the email that was provided:

http://yourdoman.com/confirm.php?hash='.$hash.'

The actual link will look something like this:

http://yourdomain.com/confirm.php?hash=00413297cc003c03d0f1ffe1cc8445f8