docs/system/tls.rst - qemu - Git at Google

 .. _network_005ftls:

 TLS setup for network services
 ------------------------------

 Almost all network services in QEMU have the ability to use TLS for
 session data encryption, along with x509 certificates for simple client
 authentication. What follows is a description of how to generate
 certificates suitable for usage with QEMU, and applies to the VNC
 server, character devices with the TCP backend, NBD server and client,
 and migration server and client.

 At a high level, QEMU requires certificates and private keys to be
 provided in PEM format. Aside from the core fields, the certificates
 should include various extension data sets, including v3 basic
 constraints data, key purpose, key usage and subject alt name.

 The GnuTLS package includes a command called ``certtool`` which can be
 used to easily generate certificates and keys in the required format
 with expected data present. Alternatively a certificate management
 service may be used.

 At a minimum it is necessary to setup a certificate authority, and issue
 certificates to each server. If using x509 certificates for
 authentication, then each client will also need to be issued a
 certificate.

 Assuming that the QEMU network services will only ever be exposed to
 clients on a private intranet, there is no need to use a commercial
 certificate authority to create certificates. A self-signed CA is
 sufficient, and in fact likely to be more secure since it removes the
 ability of malicious 3rd parties to trick the CA into mis-issuing certs
 for impersonating your services. The only likely exception where a
 commercial CA might be desirable is if enabling the VNC websockets
 server and exposing it directly to remote browser clients. In such a
 case it might be useful to use a commercial CA to avoid needing to
 install custom CA certs in the web browsers.

 The recommendation is for the server to keep its certificates in either
 ``/etc/pki/qemu`` or for unprivileged users in ``$HOME/.pki/qemu``.

 .. _tls_005fgenerate_005fca:

 Setup the Certificate Authority
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 This step only needs to be performed once per organization /
 organizational unit. First the CA needs a private key. This key must be
 kept VERY secret and secure. If this key is compromised the entire trust
 chain of the certificates issued with it is lost.

 ::

    # certtool --generate-privkey > ca-key.pem

 To generate a self-signed certificate requires one core piece of
 information, the name of the organization. A template file ``ca.info``
 should be populated with the desired data to avoid having to deal with
 interactive prompts from certtool::

    # cat > ca.info <<EOF
    cn = Name of your organization
    ca
    cert_signing_key
    EOF
    # certtool --generate-self-signed \
               --load-privkey ca-key.pem \
               --template ca.info \
               --outfile ca-cert.pem

 The ``ca`` keyword in the template sets the v3 basic constraints
 extension to indicate this certificate is for a CA, while
 ``cert_signing_key`` sets the key usage extension to indicate this will
 be used for signing other keys. The generated ``ca-cert.pem`` file
 should be copied to all servers and clients wishing to utilize TLS
 support in the VNC server. The ``ca-key.pem`` must not be
 disclosed/copied anywhere except the host responsible for issuing
 certificates.

 .. _tls_005fgenerate_005fserver:

 Issuing server certificates
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~

 Each server (or host) needs to be issued with a key and certificate.
 When connecting the certificate is sent to the client which validates it
 against the CA certificate. The core pieces of information for a server
 certificate are the hostnames and/or IP addresses that will be used by
 clients when connecting. The hostname / IP address that the client
 specifies when connecting will be validated against the hostname(s) and
 IP address(es) recorded in the server certificate, and if no match is
 found the client will close the connection.

 Thus it is recommended that the server certificate include both the
 fully qualified and unqualified hostnames. If the server will have
 permanently assigned IP address(es), and clients are likely to use them
 when connecting, they may also be included in the certificate. Both IPv4
 and IPv6 addresses are supported. Historically certificates only
 included 1 hostname in the ``CN`` field, however, usage of this field
 for validation is now deprecated. Instead modern TLS clients will
 validate against the Subject Alt Name extension data, which allows for
 multiple entries. In the future usage of the ``CN`` field may be
 discontinued entirely, so providing SAN extension data is strongly
 recommended.

 On the host holding the CA, create template files containing the
 information for each server, and use it to issue server certificates.

 ::

    # cat > server-hostNNN.info <<EOF
    organization = Name  of your organization
    cn = hostNNN.foo.example.com
    dns_name = hostNNN
    dns_name = hostNNN.foo.example.com
    ip_address = 10.0.1.87
    ip_address = 192.8.0.92
    ip_address = 2620:0:cafe::87
    ip_address = 2001:24::92
    tls_www_server
    encryption_key
    signing_key
    EOF
    # certtool --generate-privkey > server-hostNNN-key.pem
    # certtool --generate-certificate \
               --load-ca-certificate ca-cert.pem \
               --load-ca-privkey ca-key.pem \
               --load-privkey server-hostNNN-key.pem \
               --template server-hostNNN.info \
               --outfile server-hostNNN-cert.pem

 The ``dns_name`` and ``ip_address`` fields in the template are setting
 the subject alt name extension data. The ``tls_www_server`` keyword is
 the key purpose extension to indicate this certificate is intended for
 usage in a web server. Although QEMU network services are not in fact
 HTTP servers (except for VNC websockets), setting this key purpose is
 still recommended. The ``encryption_key`` and ``signing_key`` keyword is
 the key usage extension to indicate this certificate is intended for
 usage in the data session.

 The ``server-hostNNN-key.pem`` and ``server-hostNNN-cert.pem`` files
 should now be securely copied to the server for which they were
 generated, and renamed to ``server-key.pem`` and ``server-cert.pem``
 when added to the ``/etc/pki/qemu`` directory on the target host. The
 ``server-key.pem`` file is security sensitive and should be kept
 protected with file mode 0600 to prevent disclosure.

 .. _tls_005fgenerate_005fclient:

 Issuing client certificates
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~

 The QEMU x509 TLS credential setup defaults to enabling client
 verification using certificates, providing a simple authentication
 mechanism. If this default is used, each client also needs to be issued
 a certificate. The client certificate contains enough metadata to
 uniquely identify the client with the scope of the certificate
 authority. The client certificate would typically include fields for
 organization, state, city, building, etc.

 Once again on the host holding the CA, create template files containing
 the information for each client, and use it to issue client
 certificates.

 ::

    # cat > client-hostNNN.info <<EOF
    country = GB
    state = London
    locality = City Of London
    organization = Name of your organization
    cn = hostNNN.foo.example.com
    tls_www_client
    encryption_key
    signing_key
    EOF
    # certtool --generate-privkey > client-hostNNN-key.pem
    # certtool --generate-certificate \
               --load-ca-certificate ca-cert.pem \
               --load-ca-privkey ca-key.pem \
               --load-privkey client-hostNNN-key.pem \
               --template client-hostNNN.info \
               --outfile client-hostNNN-cert.pem

 The subject alt name extension data is not required for clients, so
 the ``dns_name`` and ``ip_address`` fields are not included. The
 ``tls_www_client`` keyword is the key purpose extension to indicate this
 certificate is intended for usage in a web client. Although QEMU network
 clients are not in fact HTTP clients, setting this key purpose is still
 recommended. The ``encryption_key`` and ``signing_key`` keyword is the
 key usage extension to indicate this certificate is intended for usage
 in the data session.

 The ``client-hostNNN-key.pem`` and ``client-hostNNN-cert.pem`` files
 should now be securely copied to the client for which they were
 generated, and renamed to ``client-key.pem`` and ``client-cert.pem``
 when added to the ``/etc/pki/qemu`` directory on the target host. The
 ``client-key.pem`` file is security sensitive and should be kept
 protected with file mode 0600 to prevent disclosure.

 If a single host is going to be using TLS in both a client and server
 role, it is possible to create a single certificate to cover both roles.
 This would be quite common for the migration and NBD services, where a
 QEMU process will be started by accepting a TLS protected incoming
 migration, and later itself be migrated out to another host. To generate
 a single certificate, simply include the template data from both the
 client and server instructions in one.

 ::

    # cat > both-hostNNN.info <<EOF
    country = GB
    state = London
    locality = City Of London
    organization = Name of your organization
    cn = hostNNN.foo.example.com
    dns_name = hostNNN
    dns_name = hostNNN.foo.example.com
    ip_address = 10.0.1.87
    ip_address = 192.8.0.92
    ip_address = 2620:0:cafe::87
    ip_address = 2001:24::92
    tls_www_server
    tls_www_client
    encryption_key
    signing_key
    EOF
    # certtool --generate-privkey > both-hostNNN-key.pem
    # certtool --generate-certificate \
               --load-ca-certificate ca-cert.pem \
               --load-ca-privkey ca-key.pem \
               --load-privkey both-hostNNN-key.pem \
               --template both-hostNNN.info \
               --outfile both-hostNNN-cert.pem

 When copying the PEM files to the target host, save them twice, once as
 ``server-cert.pem`` and ``server-key.pem``, and again as
 ``client-cert.pem`` and ``client-key.pem``.

 .. _tls_005fcreds_005fsetup:

 TLS x509 credential configuration
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 QEMU has a standard mechanism for loading x509 credentials that will be
 used for network services and clients. It requires specifying the
 ``tls-creds-x509`` class name to the ``--object`` command line argument
 for the system emulators. Each set of credentials loaded should be given
 a unique string identifier via the ``id`` parameter. A single set of TLS
 credentials can be used for multiple network backends, so VNC,
 migration, NBD, character devices can all share the same credentials.
 Note, however, that credentials for use in a client endpoint must be
 loaded separately from those used in a server endpoint.

 When specifying the object, the ``dir`` parameters specifies which
 directory contains the credential files. This directory is expected to
 contain files with the names mentioned previously, ``ca-cert.pem``,
 ``server-key.pem``, ``server-cert.pem``, ``client-key.pem`` and
 ``client-cert.pem`` as appropriate. It is also possible to include a set
 of pre-generated Diffie-Hellman (DH) parameters in a file
 ``dh-params.pem``, which can be created using the
 ``certtool --generate-dh-params`` command. If omitted, QEMU will
 dynamically generate DH parameters when loading the credentials.

 The ``endpoint`` parameter indicates whether the credentials will be
 used for a network client or server, and determines which PEM files are
 loaded.

 The ``verify`` parameter determines whether x509 certificate validation
 should be performed. This defaults to enabled, meaning clients will
 always validate the server hostname against the certificate subject alt
 name fields and/or CN field. It also means that servers will request
 that clients provide a certificate and validate them. Verification
 should never be turned off for client endpoints, however, it may be
 turned off for server endpoints if an alternative mechanism is used to
 authenticate clients. For example, the VNC server can use SASL to
 authenticate clients instead.

 To load server credentials with client certificate validation enabled

 .. parsed-literal::

    |qemu_system| -object tls-creds-x509,id=tls0,dir=/etc/pki/qemu,endpoint=server

 while to load client credentials use

 .. parsed-literal::

    |qemu_system| -object tls-creds-x509,id=tls0,dir=/etc/pki/qemu,endpoint=client

 Network services which support TLS will all have a ``tls-creds``
 parameter which expects the ID of the TLS credentials object. For
 example with VNC:

 .. parsed-literal::

    |qemu_system| -vnc 0.0.0.0:0,tls-creds=tls0

 .. _tls_005fpsk:

 TLS Pre-Shared Keys (PSK)
 ~~~~~~~~~~~~~~~~~~~~~~~~~

 Instead of using certificates, you may also use TLS Pre-Shared Keys
 (TLS-PSK). This can be simpler to set up than certificates but is less
 scalable.

 Use the GnuTLS ``psktool`` program to generate a ``keys.psk`` file
 containing one or more usernames and random keys::

    mkdir -m 0700 /tmp/keys
    psktool -u rich -p /tmp/keys/keys.psk

 TLS-enabled servers such as ``qemu-nbd`` can use this directory like so::

    qemu-nbd \
      -t -x / \
      --object tls-creds-psk,id=tls0,endpoint=server,dir=/tmp/keys \
      --tls-creds tls0 \
      image.qcow2

 When connecting from a qemu-based client you must specify the directory
 containing ``keys.psk`` and an optional username (defaults to "qemu")::

    qemu-img info \
      --object tls-creds-psk,id=tls0,dir=/tmp/keys,username=rich,endpoint=client \
      --image-opts \
      file.driver=nbd,file.host=localhost,file.port=10809,file.tls-creds=tls0,file.export=/
	.. _network_005ftls:

	TLS setup for network services
	------------------------------

	Almost all network services in QEMU have the ability to use TLS for
	session data encryption, along with x509 certificates for simple client
	authentication. What follows is a description of how to generate
	certificates suitable for usage with QEMU, and applies to the VNC
	server, character devices with the TCP backend, NBD server and client,
	and migration server and client.

	At a high level, QEMU requires certificates and private keys to be
	provided in PEM format. Aside from the core fields, the certificates
	should include various extension data sets, including v3 basic
	constraints data, key purpose, key usage and subject alt name.

	The GnuTLS package includes a command called ``certtool`` which can be
	used to easily generate certificates and keys in the required format
	with expected data present. Alternatively a certificate management
	service may be used.

	At a minimum it is necessary to setup a certificate authority, and issue
	certificates to each server. If using x509 certificates for
	authentication, then each client will also need to be issued a
	certificate.

	Assuming that the QEMU network services will only ever be exposed to
	clients on a private intranet, there is no need to use a commercial
	certificate authority to create certificates. A self-signed CA is
	sufficient, and in fact likely to be more secure since it removes the
	ability of malicious 3rd parties to trick the CA into mis-issuing certs
	for impersonating your services. The only likely exception where a
	commercial CA might be desirable is if enabling the VNC websockets
	server and exposing it directly to remote browser clients. In such a
	case it might be useful to use a commercial CA to avoid needing to
	install custom CA certs in the web browsers.

	The recommendation is for the server to keep its certificates in either
	``/etc/pki/qemu`` or for unprivileged users in ``$HOME/.pki/qemu``.

	.. _tls_005fgenerate_005fca:

	Setup the Certificate Authority
	~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

	This step only needs to be performed once per organization /
	organizational unit. First the CA needs a private key. This key must be
	kept VERY secret and secure. If this key is compromised the entire trust
	chain of the certificates issued with it is lost.

	::

	# certtool --generate-privkey > ca-key.pem

	To generate a self-signed certificate requires one core piece of
	information, the name of the organization. A template file ``ca.info``
	should be populated with the desired data to avoid having to deal with
	interactive prompts from certtool::

	# cat > ca.info <<EOF
	cn = Name of your organization
	ca
	cert_signing_key
	EOF
	# certtool --generate-self-signed \
	--load-privkey ca-key.pem \
	--template ca.info \
	--outfile ca-cert.pem

	The ``ca`` keyword in the template sets the v3 basic constraints
	extension to indicate this certificate is for a CA, while
	``cert_signing_key`` sets the key usage extension to indicate this will
	be used for signing other keys. The generated ``ca-cert.pem`` file
	should be copied to all servers and clients wishing to utilize TLS
	support in the VNC server. The ``ca-key.pem`` must not be
	disclosed/copied anywhere except the host responsible for issuing
	certificates.

	.. _tls_005fgenerate_005fserver:

	Issuing server certificates
	~~~~~~~~~~~~~~~~~~~~~~~~~~~

	Each server (or host) needs to be issued with a key and certificate.
	When connecting the certificate is sent to the client which validates it
	against the CA certificate. The core pieces of information for a server
	certificate are the hostnames and/or IP addresses that will be used by
	clients when connecting. The hostname / IP address that the client
	specifies when connecting will be validated against the hostname(s) and
	IP address(es) recorded in the server certificate, and if no match is
	found the client will close the connection.

	Thus it is recommended that the server certificate include both the
	fully qualified and unqualified hostnames. If the server will have
	permanently assigned IP address(es), and clients are likely to use them
	when connecting, they may also be included in the certificate. Both IPv4
	and IPv6 addresses are supported. Historically certificates only
	included 1 hostname in the ``CN`` field, however, usage of this field
	for validation is now deprecated. Instead modern TLS clients will
	validate against the Subject Alt Name extension data, which allows for
	multiple entries. In the future usage of the ``CN`` field may be
	discontinued entirely, so providing SAN extension data is strongly
	recommended.

	On the host holding the CA, create template files containing the
	information for each server, and use it to issue server certificates.

	::

	# cat > server-hostNNN.info <<EOF
	organization = Name of your organization
	cn = hostNNN.foo.example.com
	dns_name = hostNNN
	dns_name = hostNNN.foo.example.com
	ip_address = 10.0.1.87
	ip_address = 192.8.0.92
	ip_address = 2620:0:cafe::87
	ip_address = 2001:24::92
	tls_www_server
	encryption_key
	signing_key
	EOF
	# certtool --generate-privkey > server-hostNNN-key.pem
	# certtool --generate-certificate \
	--load-ca-certificate ca-cert.pem \
	--load-ca-privkey ca-key.pem \
	--load-privkey server-hostNNN-key.pem \
	--template server-hostNNN.info \
	--outfile server-hostNNN-cert.pem

	The ``dns_name`` and ``ip_address`` fields in the template are setting
	the subject alt name extension data. The ``tls_www_server`` keyword is
	the key purpose extension to indicate this certificate is intended for
	usage in a web server. Although QEMU network services are not in fact
	HTTP servers (except for VNC websockets), setting this key purpose is
	still recommended. The ``encryption_key`` and ``signing_key`` keyword is
	the key usage extension to indicate this certificate is intended for
	usage in the data session.

	The ``server-hostNNN-key.pem`` and ``server-hostNNN-cert.pem`` files
	should now be securely copied to the server for which they were
	generated, and renamed to ``server-key.pem`` and ``server-cert.pem``
	when added to the ``/etc/pki/qemu`` directory on the target host. The
	``server-key.pem`` file is security sensitive and should be kept
	protected with file mode 0600 to prevent disclosure.

	.. _tls_005fgenerate_005fclient:

	Issuing client certificates
	~~~~~~~~~~~~~~~~~~~~~~~~~~~

	The QEMU x509 TLS credential setup defaults to enabling client
	verification using certificates, providing a simple authentication
	mechanism. If this default is used, each client also needs to be issued
	a certificate. The client certificate contains enough metadata to
	uniquely identify the client with the scope of the certificate
	authority. The client certificate would typically include fields for
	organization, state, city, building, etc.

	Once again on the host holding the CA, create template files containing
	the information for each client, and use it to issue client
	certificates.

	::

	# cat > client-hostNNN.info <<EOF
	country = GB
	state = London
	locality = City Of London
	organization = Name of your organization
	cn = hostNNN.foo.example.com
	tls_www_client
	encryption_key
	signing_key
	EOF
	# certtool --generate-privkey > client-hostNNN-key.pem
	# certtool --generate-certificate \
	--load-ca-certificate ca-cert.pem \
	--load-ca-privkey ca-key.pem \
	--load-privkey client-hostNNN-key.pem \
	--template client-hostNNN.info \
	--outfile client-hostNNN-cert.pem

	The subject alt name extension data is not required for clients, so
	the ``dns_name`` and ``ip_address`` fields are not included. The
	``tls_www_client`` keyword is the key purpose extension to indicate this
	certificate is intended for usage in a web client. Although QEMU network
	clients are not in fact HTTP clients, setting this key purpose is still
	recommended. The ``encryption_key`` and ``signing_key`` keyword is the
	key usage extension to indicate this certificate is intended for usage
	in the data session.

	The ``client-hostNNN-key.pem`` and ``client-hostNNN-cert.pem`` files
	should now be securely copied to the client for which they were
	generated, and renamed to ``client-key.pem`` and ``client-cert.pem``
	when added to the ``/etc/pki/qemu`` directory on the target host. The
	``client-key.pem`` file is security sensitive and should be kept
	protected with file mode 0600 to prevent disclosure.

	If a single host is going to be using TLS in both a client and server
	role, it is possible to create a single certificate to cover both roles.
	This would be quite common for the migration and NBD services, where a
	QEMU process will be started by accepting a TLS protected incoming
	migration, and later itself be migrated out to another host. To generate
	a single certificate, simply include the template data from both the
	client and server instructions in one.

	::

	# cat > both-hostNNN.info <<EOF
	country = GB
	state = London
	locality = City Of London
	organization = Name of your organization
	cn = hostNNN.foo.example.com
	dns_name = hostNNN
	dns_name = hostNNN.foo.example.com
	ip_address = 10.0.1.87
	ip_address = 192.8.0.92
	ip_address = 2620:0:cafe::87
	ip_address = 2001:24::92
	tls_www_server
	tls_www_client
	encryption_key
	signing_key
	EOF
	# certtool --generate-privkey > both-hostNNN-key.pem
	# certtool --generate-certificate \
	--load-ca-certificate ca-cert.pem \
	--load-ca-privkey ca-key.pem \
	--load-privkey both-hostNNN-key.pem \
	--template both-hostNNN.info \
	--outfile both-hostNNN-cert.pem

	When copying the PEM files to the target host, save them twice, once as
	``server-cert.pem`` and ``server-key.pem``, and again as
	``client-cert.pem`` and ``client-key.pem``.

	.. _tls_005fcreds_005fsetup:

	TLS x509 credential configuration
	~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

	QEMU has a standard mechanism for loading x509 credentials that will be
	used for network services and clients. It requires specifying the
	``tls-creds-x509`` class name to the ``--object`` command line argument
	for the system emulators. Each set of credentials loaded should be given
	a unique string identifier via the ``id`` parameter. A single set of TLS
	credentials can be used for multiple network backends, so VNC,
	migration, NBD, character devices can all share the same credentials.
	Note, however, that credentials for use in a client endpoint must be
	loaded separately from those used in a server endpoint.

	When specifying the object, the ``dir`` parameters specifies which
	directory contains the credential files. This directory is expected to
	contain files with the names mentioned previously, ``ca-cert.pem``,
	``server-key.pem``, ``server-cert.pem``, ``client-key.pem`` and
	``client-cert.pem`` as appropriate. It is also possible to include a set
	of pre-generated Diffie-Hellman (DH) parameters in a file
	``dh-params.pem``, which can be created using the
	``certtool --generate-dh-params`` command. If omitted, QEMU will
	dynamically generate DH parameters when loading the credentials.

	The ``endpoint`` parameter indicates whether the credentials will be
	used for a network client or server, and determines which PEM files are
	loaded.

	The ``verify`` parameter determines whether x509 certificate validation
	should be performed. This defaults to enabled, meaning clients will
	always validate the server hostname against the certificate subject alt
	name fields and/or CN field. It also means that servers will request
	that clients provide a certificate and validate them. Verification
	should never be turned off for client endpoints, however, it may be
	turned off for server endpoints if an alternative mechanism is used to
	authenticate clients. For example, the VNC server can use SASL to
	authenticate clients instead.

	To load server credentials with client certificate validation enabled

	.. parsed-literal::

	\|qemu_system\| -object tls-creds-x509,id=tls0,dir=/etc/pki/qemu,endpoint=server

	while to load client credentials use

	.. parsed-literal::

	\|qemu_system\| -object tls-creds-x509,id=tls0,dir=/etc/pki/qemu,endpoint=client

	Network services which support TLS will all have a ``tls-creds``
	parameter which expects the ID of the TLS credentials object. For
	example with VNC:

	.. parsed-literal::

	\|qemu_system\| -vnc 0.0.0.0:0,tls-creds=tls0

	.. _tls_005fpsk:

	TLS Pre-Shared Keys (PSK)
	~~~~~~~~~~~~~~~~~~~~~~~~~

	Instead of using certificates, you may also use TLS Pre-Shared Keys
	(TLS-PSK). This can be simpler to set up than certificates but is less
	scalable.

	Use the GnuTLS ``psktool`` program to generate a ``keys.psk`` file
	containing one or more usernames and random keys::

	mkdir -m 0700 /tmp/keys
	psktool -u rich -p /tmp/keys/keys.psk

	TLS-enabled servers such as ``qemu-nbd`` can use this directory like so::

	qemu-nbd \
	-t -x / \
	--object tls-creds-psk,id=tls0,endpoint=server,dir=/tmp/keys \
	--tls-creds tls0 \
	image.qcow2

	When connecting from a qemu-based client you must specify the directory
	containing ``keys.psk`` and an optional username (defaults to "qemu")::

	qemu-img info \
	--object tls-creds-psk,id=tls0,dir=/tmp/keys,username=rich,endpoint=client \
	--image-opts \
	file.driver=nbd,file.host=localhost,file.port=10809,file.tls-creds=tls0,file.export=/