Abstract: A system enables a user to remove a file from a file system and from all backup tapes without ever mounting a single tape. When a file is backed up, it is first encrypted using a randomly generated key and then backed up. When the user wishes to remove the file from the backup tape, the key used to encrypt the file is deleted. Deleting the encryption key renders the data on the tape inaccessible. No one, including the file owner, can ever access the file again. The encrypt before-backup method is completely transparent to the user. Only the computer system's operating system knows which key was used to encrypt the file during backup. This ensures that when the operating system is instructed to delete the encryption key, the key is "lost" forever and thus the backed up files become unreadable. Unlike prior cryptographic file systems, the revoked backup files are inaccessible to both the user and others.