I have been using Symmetric (Rijndael) Key Algorithm (<http://www.obviex.com/samples/Encryption.aspx>) for a while to encrypt an ID. Then I URL encode the encrypted version of the ID and pass it in the query string. When I retrieve the ID from the query string, I URL decode it first and I decrypt it.

A problem came up recently. If the encrypted ID has both "spaces" and "+" (eg "abc ef+g), URL-encoding it changes all "spaces" to "+". This is a problem when I URL-decode the ID since I don't know which "+" was a "+" and which "+" was a "space".

If there an option that I can pick the output character set to be only the alphabet (ie the encrypted ID only uses A-Z)? Or if there any other 2 way encryption algorithm that has th option for me to pick the output character set?

Or I guess my last option would be to manually replace "+" in the encrypted ID with something like "\_SPACE\_"

Thanks