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Encrypting parts of backups.

If you want to make sure data is unreadable for 3rd parties (including us), then you can opt to encrypt the data before it gets sent over the wire. The network traffic will be encrypted once again since our clients always encrypt data over the wire, and it will land on disks which are encrypted-at-rest, which means it will be encrypted twice, but the inner encryption is something you will have full control over. Options mentioned below go into:

C:\Program Files\tivoli\tsm\baclient\dsm.opt
/Library/Application Support/tivoli/tsm/client/ba/bin/dsm.sys

If you are going to use encryption, you will probably want to move from the default AES128 to AES256 with this option: Encryptiontype aes256.

How to handle keys

First of all, there is nothing that prevents you from using external crypto software using whatever key scheme, the only change as far as the service goes is that deduplication and compression will not yield any gains.

When creating a node when you know all data will be encrypted, selecting Encryption will make sure neither client nor server will attempt dedup or compression to prevent waste of computing resources. It is not a hard requirement and if you want to encrypt only parts of it, select deduplication and compression as normal, then use options (described below) to point out the specific folders to encrypt.

Selecting encryption while creating the node will push server config to the client going INCLUDE.ENCRYPT /.../* to make sure all files are secure at first run.

IBM client encryption

If you want to let the IBM client do the encryption you have to select if and how to store the encryption key. The choices are:

  1. Never store the key at all. This forces you to enter the key for every backup and restore operation. Very cumbersome but ultimately the safest option if you decide not to trust the backup operators at all, or want the same level as using a completely separate encryption program manually. Enabled with ENCRYPTKEY prompt.

  2. Randomize a per-node key and store it on the local drive. This will allow automated backups and restores as long as the client node still has its drive working. For Bare Metal restores you need to have an offline copy of the key at your place. Enabled with ENCRYPTKEY save Should be combined with PASSWORDACCESS generate which means the key is stashed encrypted on disk, accessible by the program but not readable by humans. If your machine in turn has an encrypted root disk which requires password entry at boot, it will still be protected from "evil maid" scenarios where someone copies your drive when it is turned off and tries to use the data offline.

  3. Generate a key and store it in the backup server database. Sounds a bit weird, but is meant to protect situations similar to having backup tapes sent via untrusted couriers to external cold storage. In this case a lost/stolen tape will be unreadable for anyone not in control of the running backup server. Not very applicable to our service, and our encryption-at-rest should cover the risk of someone stealing a disk from us with your backups on. Enabled with ENCRYPTKEY generate.

Selecting what to encrypt

To cover the whole disk, something simple like the following example will make all files on all drives and filesystems that are backed up to be encrypted before transfer.

INCLUDE.encrypt "/.../*"
INCLUDE.encrypt ?:\...\*

Do mind that it will not affect files that have already been sent over previously, which may confuse people testing encryption on a node for which normal backups have been done before. Touching or editing a file that is (now) covered by a INCLUDE.encrypt statement will make next backup be encrypted, but the old unencrypted version will linger until it expires depending on the retention polices it was backed up under.

Also, this will still store directory and file names in clear text in the database to be able to selectively make single file restores, but the contents of encrypted files will be unavailable until the correct key has been supplied.

Encrypting selected folders

If you want to selectively encrypt a subset of the data, add something along the lines of this to your dsm.opt / dsm.sys file:

INCLUDE.ENCRYPT "/Users/username/secret2/.../*"
INCLUDE.ENCRYPT "/Users/username/secret/.../*"
INCLUDE.ENCRYPT "/Users/username/private/.../*"

which means most of the files can get the normal deduplication and compression gains, but when the backup client passes by files in these three folders and their subfolders, they will be encrypted.

Output from a backup run

From a run with some files matching INCLUDE.encrypt:

Total number of objects inspected:           24
Total number of objects backed up:            5
Total number of objects updated:             19
Total number of objects rebound:              0
Total number of objects deleted:              0
Total number of objects expired:              0
Total number of objects failed:               0
Total number of objects encrypted:            4
Data encryption type:               256-bit AES

Read more on IBMs site