This is going to be a little long and rambly, but I want to make sure everything is in the proper context.
Back in 2004 I wrote an online Learning Management System using Classic ASP and VBScript. I'm now working on some upgrades (and periodically asking myself WTF I was thinking when I wrote various segments of code...), and I want to take this opportunity to resolve one of the frequent complaints I get - the size of the verification numbers.
When you complete a test online, a verification number is displayed so if you needed to re-create your certificate of completion (its a hospital, and trying to get them to get rid of their paper is like asking Linus to give up his blanket) you can enter the number, etc. etc.
At the time I wrote it (and sadly still to this day) there is no unique identifier I can use to create a transcript page - so please don't post suggestions to that end. There's more going on than I care to get into, and I want to head off valid suggestions that I can't use. ;)
The verification number is a concatenation of various pieces of information (mostly because when I first wrote it I was an idiot newb and SO wasn't around), and while it is a much-appreciated feature there are a lot of complaints about how long the number is. Returning the raw ID at this point is no better as we're in the 6-digit range.
My initial idea was to use a Base64 encoding algorithm I got from elsewhere, but given the problems I've had with just numbers, I'm thinking changing it to a case-sensitive value is only asking for a different class of problems... which brings me to the question at hand:
What can I use to create the shortest possible case-insensitive verification number since hex won't reduce the length appreciably?
And as the tags indicate, I need to be able to implement it in ASP Classic/VBScript - migration is not an option at this point.
Edit: based on the answers, I found a link to Crockfor's implementation of Base32, which looks like what I'm looking for - http://www.crockford.com/wrmg/base32.html