shorter php cipher than md5?
maybe this will help you generate a 12 char string that you can pass in a URL, without increasing the risk of collisions
substr(base_convert(md5($string), 16,32), 0, 12);
This is an addition to this answer.
The answer proposes to take the first twelve characters from a 32 character representation of md5. Thus 20 characters of information will be lost - this will result in way more possible collisions.
You can reduce the loss of information by taking the first twelve characters of a 16 character representation (the raw form):
substr(md5($string, true), 0, 12);This will maintain 75% of the data, whereas the use of the 32 char form only maintains 37.5% of the data.