First though I have is a kind of function that returns a key base on some well know variables like: date when the backup run, user in charge of the backup and machine where the database is placed, and finally a variable value that few people know (you and another one). If the name of the backup include all the variables values (i.e. BCK_DDMMYYYY_NAME_XXXXBOX) except obviously the "secret" variable value, you can retrieve the password for the back up whenever you want and independently of who generate the backup and when it was generated.

The function to generate the variable should be protected accordingly.