GeoTools (and GeoServer) provide EPSG:404000 for generic 2D systems. Search for GENERIC_2D in http://docs.geotools.org/latest/userguide/library/referencing/crs.html for details. 

I've never tried to use it myself but I think it should do what you need.

Force Geoserver SRID 0
I want to encrypt a small piece of data that is less that 16 bytes in size (think SSN), and I'll be using a 256bit encryption key.  The typical suggestion is to never use ECB, but if there is just a single block being encrypted, is it a concern?

The reason I want to use ECB is because I want the encrypted value of the block to be consistent between encryptions for other reasons (so I can check if a value already exists by just comparing the uniqueness of the cipherText).

Updated: Also note that these encrypted values will be stored in a set, so there will not be data leakage by having multiple encrypted values of the same plainText available.
