Encrypt Content In XML

I will have security rights stored in XML data, and I just need the content
of elements and/or attributes to be encrypted. When the dotnet application
reads in the information, it would run a simple decryption on the data. I
have one routine that does this, except is uses hexadecimal characters, so I
need it to be valid characters for xml. Any routines out there to do this,
encrypt and decrypt data that can be used in XML?

Derek