Notice

This document is for a development version of Ceph.

Encryption

Logical volumes can be encrypted using dmcrypt by specifying the --dmcrypt flag when creating OSDs. When using LVM, logical volumes can be encrypted in different ways. ceph-volume does not offer as many options as LVM does, but it encrypts logical volumes in a way that is consistent and robust.

In this case, ceph-volume lvm follows this constraint:

  • Non-LVM devices (such as partitions) are encrypted with the same OSD key.

LUKS

There are currently two versions of LUKS, 1 and 2. Version 2 is a bit easier to implement but not widely available in all Linux distributions supported by Ceph.

Note

Version 1 of LUKS is referred to in this documentation as “LUKS”. Version 2 is of LUKS is referred to in this documentation as “LUKS2”.

LUKS on LVM

Encryption is done on top of existing logical volumes (this is not the same as encrypting the physical device). Any single logical volume can be encrypted, leaving other volumes unencrypted. This method also allows for flexible logical volume setups, since encryption will happen once the LV is created.

Workflow

When setting up the OSD, a secret key is created. That secret key is passed to the monitor in JSON format as stdin to prevent the key from being captured in the logs.

The JSON payload looks something like this:

{
    "cephx_secret": CEPHX_SECRET,
    "dmcrypt_key": DMCRYPT_KEY,
    "cephx_lockbox_secret": LOCKBOX_SECRET,
}

The naming convention for the keys is strict, and they are named like that for the hardcoded (legacy) names used by ceph-disk.

  • cephx_secret : The cephx key used to authenticate

  • dmcrypt_key : The secret (or private) key to unlock encrypted devices

  • cephx_lockbox_secret : The authentication key used to retrieve the dmcrypt_key. It is named lockbox because ceph-disk used to have an unencrypted partition named after it, which was used to store public keys and other OSD metadata.

The naming convention is strict because Monitors supported the naming convention of ceph-disk, which used these key names. In order to maintain compatibility and prevent ceph-disk from breaking, ceph-volume uses the same naming convention although it does not make sense for the new encryption workflow.

After the common steps of setting up the OSD during the “prepare stage” (either with filestore or bluestore), the logical volume is left ready to be activated, regardless of the state of the device (encrypted or decrypted).

At the time of its activation, the logical volume is decrypted. The OSD starts after the process completes correctly.

Summary of the encryption workflow for creating a new OSD

  1. OSD is created. Both lockbox and dmcrypt keys are created and sent to the monitors in JSON format, indicating an encrypted OSD.

  2. All complementary devices (like journal, db, or wal) get created and encrypted with the same OSD key. Key is stored in the LVM metadata of the OSD.

  3. Activation continues by ensuring devices are mounted, retrieving the dmcrypt secret key from the monitors, and decrypting before the OSD gets started.