Unique key generation

Question

I looking for a way, specifically in PHP that I will be guaranteed to always get a unique key.

I have done the following:

strtolower(substr(crypt(tim         


        

Answer 1

I usually do it like this:

$this->password = '';

for($i=0; $i<10; $i++)
{
    if($i%2 == 0)
        $this->password .= chr(rand(65,90));
    if($i%3 == 0)
        $this->password .= chr(rand(97,122));
    if($i%4 == 0)
        $this->password .= chr(rand(48,57));
}

I suppose there are some theoretical holes but I've never had an issue with duplication. I usually use it for temporary passwords (like after a password reset) and it works well enough for that.