thanks a lot for your reply. probably, I was not very clear - it's not BACKUP encryption I'm after (this is OK - have it working already, used your notes too
Now we decided to encrypt the DATABASE (user tablespaces to be exact) rather than backup. Did that but found that I can't replicate the database; I normally use rman duplicate to do the database refreshes (e.g. production into test etc) - its fails when I try it on encrypted db.