Using_Encryption

   BACKUP can create and restore encrypted save sets.

   Using encryption may be required due to your data archival security
   policy or for transferring files via non-secure channels.
   Additional CPU time is required to process encrypted files.

   See the /ENCRYPT qualifier for details.

   Note that when simultaneously using both compression and encryption
   to create a save set, the data is encrypted first.  This means
   that very little data compression can then be accomplished.