References on best practices for registration keys/access codes format

Question

I am developing an online site to which access will be sold at college bookstores. Students will purchase a card at the bookstore with an access code that they may then use to register online at our site.

I want to make the code as user friendly as possible. I personally hate registering for a product and having to type in a registration key 5 times because it's ambiguous.

Can anyone point me to resources describing best practices for designing the format of the code itself? Obvious things spring to mind-- don't use zeroes or the letter O, don't make it case sensitive, include some kind of checksum. I don't want to be creative here, I need a recipe for what must be a problem solved many times.

Answer 1

It really depends on how much security you need. A few ideas come to mind.

If you want something really simple you could generate simulated credit card numbers; students are adept at using these four-digit combinations, and they can be checked with a Luhn algorithm.

If you want something a little stronger you could generate a GUID, and use that as the code.

If your website can send emails you can ask the student for their email address, and send them a challenge/response email. Then you don't need codes at all. Their email address is the code.

Answer 2

Joel Spolsky had some good insights to solving this problem in one of the recent StackOverflow podcasts. I believe the episode was #49, you should download podcasts or checkout the transcripts at https://stackoverflow.fogbugz.com/default.asp?W4

Dealing with 0 (number) and O (letter) mixed in a key is really annoying as some fonts make it hard to distinguish the two.

Other usability concepts such as groups of three being easier to deal with and remember then a single number are good to be aware of. For example, 345-829-817-432 instead of 345829817432.

By the way, 345-829-817-432 gives you 12^10 permutations, and even the smaller number 345-829-817 gives you 9^10 permutations which may give you enough strength depending on your situation.

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