You should be cautious when you delete encryption keys. When you delete an encryption key, you cannot restore the backup sets that you encrypted with that key unless you create a new key that uses the same encryption key and pass phrase as the original key.
You can delete encryption keys in the following situations:
The encryption key is not being used in a selection list for restore jobs and for verify duplicate backup set jobs. If you delete a key that is being used in one of the listed job types, the selection list can no longer be used.
To delete an encryption key