libvirt: Storage volume encryption XML format
Description: libvirt, virtualization, virtualization API

# Storage volume encryption XML format

- Storage volume encryption XML
  - "default" format
  - "qcow" format
  - "luks" format
- Examples

## Storage volume encryption XML

Storage volumes may be encrypted, the XML snippet described below is used to represent the details of the encryption. It can be used as a part of a domain or storage configuration.

The top-level tag of volume encryption specification is `encryption`, with a mandatory attribute `format`. Currently defined values of `format` are `default`, `qcow`, and `luks`. Each value of `format` implies some expectations about the content of the `encryption` tag. Other format values may be defined in the future.

The `encryption` tag can currently contain a sequence of `secret` tags, each with mandatory attributes `type` and either `uuid` or `usage` (since 2.1.0). The only currently defined value of `type` is `volume`. The `uuid` is "uuid" of the `secret` while `usage` is the "usage" subelement field. A secret value can be set in libvirt by the `virSecretSetValue` API. Alternatively, if supported by the particular volume format and driver, automatically generate a secret value at the time of volume creation, and store it using the specified `uuid`.

### "default" format

`<encryption format="default"/>` can be specified only when creating a qcow volume. If the volume is successfully created, the encryption formats, parameters and secrets will be auto-generated by libvirt and the attached `encryption` tag will be updated. The unmodified contents of the `encryption` tag can be used in later operations with the volume, or when setting up a domain that uses the volume.

### "qcow" format

The `qcow` format specifies that the built-in encryption support in `qcow`- or `qcow2`-formatted volume images should be used. A single `<secret type='passphrase'>` element is expected. If the `secret` element is not present during volume creation, a secret is automatically generated and attached to the volume.

### "luks" format

The `luks` format is specific to a luks encrypted volume and the secret is used in order to either encrypt during volume creation or decrypt the volume for usage by the domain. A single `<secret type='passphrase'...>` element is expected. Since 2.1.0.

For volume creation, it is possible to specify the encryption algorithm used to encrypt the luks volume. The following two optional elements may be provided for that purpose. It is hypervisor dependent as to which algorithms are supported. The default algorithm used by the storage driver backend when using qemu-img to create the volume is 'aes-256-cbc' using 'essiv' for initialization vector generation and 'sha256' hash algorithm for both the cipher and the initialization vector generation.

`cipher`
  This element describes the cipher algorithm to be used to either encrypt or decrypt the luks volume. This element has the following attributes:
  `name`
    The name of the cipher algorithm used for data encryption, such as 'aes', 'des', 'cast5', 'serpent', 'twofish', etc. Support of the specific algorithm is storage driver implementation dependent.
  `size`
    The size of the cipher in bits, such as '256', '192', '128', etc. Support of the specific size for a specific cipher is hypervisor dependent.
  `mode`
    An optional cipher algorithm mode such as 'cbc', 'xts', 'ecb', etc. Support of the specific cipher mode is hypervisor dependent.
  `hash`
    An optional master key hash algorithm such as 'md5', 'sha1', 'sha256', etc. Support of the specific hash algorithm is hypervisor dependent.
`ivgen`
  This optional element describes the initialization vector generation algorithm used in conjunction with the `cipher`. If the `cipher` is not provided, then an error will be generated by the parser.
  `name`
    The name of the algorithm, such as 'plain', 'plain64', 'essiv', etc. Support of the specific algorithm is hypervisor dependent.
  `hash`
    An optional hash algorithm such as 'md5', 'sha1', 'sha256', etc. Support of the specific ivgen hash algorithm is hypervisor dependent.

## Examples

Here is a simple example, specifying use of the `qcow` format:

    <encryption format='qcow'>
       <secret type='passphrase' uuid='c1f11a6d-8c5d-4a3e-ac7a-4e171c5e0d4a' />
    </encryption>

Assuming a `luks volume type secret` is already defined, a simple example specifying use of the `luks` format for either volume creation without a specific cipher being defined or as part of a domain volume definition:

    <encryption format='luks'>
      <secret type='passphrase' uuid='f52a81b2-424e-490c-823d-6bd4235bc572'/>
    </encryption>

Here is an example specifying use of the `luks` format for a specific cipher algorithm for volume creation:

    <volume>
      <name>twofish.luks</name>
      <capacity unit='G'>5</capacity>
      <target>
        <path>/var/lib/libvirt/images/demo.luks</path>
        <format type='raw'/>
        <encryption format='luks'>
           <secret type='passphrase' uuid='f52a81b2-424e-490c-823d-6bd4235bc572'/>
           <cipher name='twofish' size='256' mode='cbc' hash='sha256'/>
           <ivgen name='plain64' hash='sha256'/>
        </encryption>
      </target>
    </volume>