Sorry of the late posting... Im a new memeber

If this is still an issue for you read below. If you would like to see some source code let me know.
I have had a need to encrypt Querystrings on my websites in the past. My solution was to "borrow" the RC4 encoding and decoding algorithms and created a VB DLL, ASP function, and an Actuate Libaray tool capable of perform this task. This is the same formula that was used by PGP about 5 years ago, and my still be inuse for all I know.
Your can store the Key in your database, or a var in your code,
and then store the encrypted output in you Database, or transmit it ... or whatever...
SideNote about the RC4 Encryption formula: Someone apparenlty published this algorithm about 10 years ago on a newsgroup. I found the posting and wrote some VBScript code that does the same thing.