libvirt/docs/formatsecret.rst

Secret XML format

Secret XML

Secrets stored by libvirt may have attributes associated with them, using the secret element. The secret element has two optional attributes, each with values 'yes' and 'no', and defaulting to 'no':

ephemeral

This secret must only be kept in memory, never stored persistently.

private

The value of the secret must not be revealed to any caller of libvirt, nor to any other node.

The top-level secret element may contain the following elements:

uuid

An unique identifier for this secret (not necessarily in the UUID format). If omitted when defining a new secret, a random UUID is generated.

description

A human-readable description of the purpose of the secret.

usage

Specifies what this secret is used for. A mandatory type attribute specifies the usage category, currently only volume, ceph, iscsi, tls, and vtpm are defined. Specific usage categories are described below.

Usage type "volume"

This secret is associated with a volume, whether the format is either for a "luks" encrypted volume. Each volume will have a unique secret associated with it and it is safe to delete the secret after the volume is deleted. The <usage type='volume'> element must contain a single volume element that specifies the path of the volume this secret is associated with. For example, create a volume-secret.xml file as follows:

<secret ephemeral='no' private='yes'>
   <description>Super secret name of my first puppy</description>
   <uuid>0a81f5b2-8403-7b23-c8d6-21ccc2f80d6f</uuid>
   <usage type='volume'>
      <volume>/var/lib/libvirt/images/puppyname.img</volume>
   </usage>
</secret>

Define the secret and set the passphrase as follows:

# virsh secret-define volume-secret.xml
Secret 0a81f5b2-8403-7b23-c8d6-21ccc2f80d6f created

See Setting secret values in virsh on how to set the value of the secret using virsh secret-set-value.

The volume type secret can be supplied either in volume XML during creation of a storage volume in order to provide the passphrase to encrypt the volume or in domain XML disk device in order to provide the passphrase to decrypt the volume, since 2.1.0. An example follows:

# cat luks-secret.xml
<secret ephemeral='no' private='yes'>
   <description>LUKS Sample Secret</description>
   <uuid>f52a81b2-424e-490c-823d-6bd4235bc57</uuid>
   <usage type='volume'>
      <volume>/var/lib/libvirt/images/luks-sample.img</volume>
   </usage>
</secret>

# virsh secret-define luks-secret.xml
Secret f52a81b2-424e-490c-823d-6bd4235bc57 created

See Setting secret values in virsh on how to set the value of the secret using virsh secret-set-value.

The volume type secret can be supplied in domain XML for a luks storage volume encryption as follows:

<encryption format='luks'>
  <secret type='passphrase' uuid='f52a81b2-424e-490c-823d-6bd4235bc57'/>
</encryption>

Usage type "ceph"

This secret is associated with a Ceph RBD (rados block device). The <usage type='ceph'> element must contain a single name element that specifies a usage name for the secret. The Ceph secret can then be used by UUID or by this usage name via the <auth> element of a disk device or a storage pool (rbd). Since 0.9.7. The following is an example of the steps to be taken. First create a ceph-secret.xml file:

<secret ephemeral='no' private='yes'>
   <description>CEPH passphrase example</description>
   <usage type='ceph'>
      <name>ceph_example</name>
   </usage>
</secret>

Next, use virsh secret-define ceph-secret.xml to define the secret and virsh secret-set-value using the generated UUID value and a base64 generated secret value in order to define the chosen secret pass phrase.

# virsh secret-define ceph-secret.xml
Secret 1b40a534-8301-45d5-b1aa-11894ebb1735 created
#
# virsh secret-list
 UUID                                 Usage
-----------------------------------------------------------
 1b40a534-8301-45d5-b1aa-11894ebb1735 cephx ceph_example

See Setting secret values in virsh on how to set the value of the secret using virsh secret-set-value.

The ceph secret can then be used by UUID or by the usage name via the <auth> element in a domain's <disk> <formatdomain.html#hard-drives-floppy-disks-cdroms>__ element as follows:

<auth username='myname'>
  <secret type='ceph' usage='ceph_example'/>
</auth>

As well as the <auth> element in a storage pool (rbd) <source> element as follows:

<auth type='ceph' username='myname'>
  <secret usage='ceph_example'/>
</auth>

Usage type "iscsi"

This secret is associated with an iSCSI target for CHAP authentication. The <usage type='iscsi'> element must contain a single target element that specifies a usage name for the secret. The iSCSI secret can then be used by UUID or by this usage name via the <auth> element of a disk device or a storage pool (iscsi). Since 1.0.4. The following is an example of the XML that may be used to generate a secret for iSCSI CHAP authentication. Assume the following sample entry in an iSCSI authentication file:

<target iqn.2013-07.com.example:iscsi-pool>
backing-store /home/tgtd/iscsi-pool/disk1
backing-store /home/tgtd/iscsi-pool/disk2
incominguser myname mysecret
</target>

Define an iscsi-secret.xml file to describe the secret. Use the incominguser username used in your iSCSI authentication configuration file as the value for the username attribute. The description attribute should contain configuration specific data. The target name may be any name of your choosing to be used as the usage when used in the pool or disk XML description.

<secret ephemeral='no' private='yes'>
   <description>Passphrase for the iSCSI example.com server</description>
   <usage type='iscsi'>
      <target>libvirtiscsi</target>
   </usage>
</secret>

Next, use virsh secret-define iscsi-secret.xml to define the secret and virsh secret-set-value using the generated UUID value and a base64 generated secret value in order to define the chosen secret pass phrase. The pass phrase must match the password used in the iSCSI authentication configuration file.

# virsh secret-define secret.xml
Secret c4dbe20b-b1a3-4ac1-b6e6-2ac97852ebb6 created

# virsh secret-list
 UUID                                 Usage
-----------------------------------------------------------
 c4dbe20b-b1a3-4ac1-b6e6-2ac97852ebb6 iscsi libvirtiscsi

See Setting secret values in virsh on how to set the value of the secret using virsh secret-set-value.

The iSCSI secret can then be used by UUID or by the usage name via the <auth> element in a domain's <disk> <formatdomain.html#hard-drives-floppy-disks-cdroms>__ element as follows:

<auth username='myname'>
  <secret type='iscsi' usage='libvirtiscsi'/>
</auth>

As well as the <auth> element in a storage pool (iscsi) <source> element as follows:

<auth type='chap' username='myname'>
  <secret usage='libvirtiscsi'/>
</auth>

Usage type "tls"

This secret may be used in order to provide the passphrase for the private key used to provide TLS credentials. The <usage type='tls'> element must contain a single name element that specifies a usage name for the secret. Since 2.3.0. The following is an example of the expected XML and processing to define the secret:

# cat tls-secret.xml
<secret ephemeral='no' private='yes'>
   <description>sample tls secret</description>
   <usage type='tls'>
      <name>TLS_example</name>
   </usage>
</secret>

# virsh secret-define tls-secret.xml
Secret 718c71bd-67b5-4a2b-87ec-a24e8ca200dc created

# virsh secret-list
 UUID                                 Usage
-----------------------------------------------------------
 718c71bd-67b5-4a2b-87ec-a24e8ca200dc  tls TLS_example

A secret may also be defined via the virSecretDefineXML API. Once the secret is defined, a secret value will need to be set. The secret would be the passphrase used to access the TLS credentials. The following is a simple example of using virsh secret-set-value to set the secret value. The virSecretSetValue API may also be used to set a more secure secret without using printable/readable characters.

Usage type "vtpm"

This secret is associated with a virtualized TPM (vTPM) and serves as a passphrase for deriving a key from for encrypting the state of the vTPM. The <usage type='vtpm'> element must contain a single name element that specifies a usage name for the secret. The vTPM secret can then be used by UUID via the <encryption> element of a tpm when using an emulator. Since 5.6.0. The following is an example of the steps to be taken. First create a vtpm-secret.xml file:

# cat vtpm-secret.xml
<secret ephemeral='no' private='yes'>
   <description>sample vTPM secret</description>
   <usage type='vtpm'>
      <name>VTPM_example</name>
   </usage>
</secret>

# virsh secret-define vtpm-secret.xml
Secret 6dd3e4a5-1d76-44ce-961f-f119f5aad935 created

# virsh secret-list
 UUID                                   Usage
----------------------------------------------------------------------------------------
 6dd3e4a5-1d76-44ce-961f-f119f5aad935   vtpm VTPM_example

A secret may also be defined via the virSecretDefineXML API. Once the secret is defined, a secret value will need to be set. The secret would be the passphrase used to decrypt the vTPM state. The following is a simple example of using virsh secret-set-value to set the secret value. The virSecretSetValue API may also be used to set a more secure secret without using printable/readable characters.

Setting secret values in virsh

To set the value of the secret you can use the following virsh commands. If the secret is a password-like string (printable characters, no newline) you can use:

# virsh secret-set-value --interactive 6dd3e4a5-1d76-44ce-961f-f119f5aad935
Enter new value for secret:
Secret value set

Another secure option is to read the secret from a file. This way the secret can contain any bytes (even NUL and non-printable characters). The length of the secret is the length of the input file. Alternatively the --plain option can be omitted if the file contents are base64-encoded.

# virsh secret-set-value 6dd3e4a5-1d76-44ce-961f-f119f5aad935 --file --plain secretinfile
Secret value set

WARNING The following approach is insecure and deprecated. The secret can also be set via an argument. Note that other users may see the actual secret in the process listing! The secret must be base64 encoded.

# MYSECRET=`printf %s "open sesame" | base64`
# virsh secret-set-value 6dd3e4a5-1d76-44ce-961f-f119f5aad935 $MYSECRET
Secret value set