PHP: Generate random password

function generatePassword ($length = 8)
{

// start with a blank password
$password = "";

// define possible characters
$possible = "0123456789bcdfghjkmnpqrstvwxyz";

// set up a counter
$i = 0;

// add random characters to $password until $length is reached
while ($i < $length) {

// pick a random character from the possible ones
$char = substr($possible, mt_rand(0, strlen($possible)-1), 1);

// we don't want this character if it's already in the password
if (!strstr($password, $char)) {
$password .= $char;
$i++;
}

}

// done!
return $password;

}