Administrator Guide : Security : Encryption : Making backups of encrypted databases
  
Making backups of encrypted databases
When you create a backup or netbackup of an encrypted database, the backup database is encrypted with the same encryption key and password.
If you use netbackup and your database is encrypted using IBM Global Security Kit (GSKit), the GSKit must be enabled and available on the netbackup server. Also, you might need to restart the netbackup server after making a netbackup of an database that is encrypted with GSKit.
See also
Encryption