Storage volume encryption XML format
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 ¶
"qcow" format ¶
Since 4.5.0, encryption formats
default
and qcow
may no longer be used
to create an encrypted volume. Usage of qcow encrypted volumes
in QEMU began phasing out in QEMU 2.3 and by QEMU 2.9 creation
of a qcow encrypted volume via qemu-img required usage of secret
objects, but that support was not added to libvirt.
"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 thecipher
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 ¶
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>