On Thu, Oct 30, 2025 at 6:50 PM Daniel P. Berrangé <berrange@redhat.com>
wrote:
> Explain how to alter the certtool commands for creating certficates,
> so that they can use algorithms that are compliant with post-quantum
> crytography standards.
>
> Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> ---
> docs/system/tls.rst | 68 +++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 68 insertions(+)
>
> diff --git a/docs/system/tls.rst b/docs/system/tls.rst
> index 7cec4ac3df..03fa1d8166 100644
> --- a/docs/system/tls.rst
> +++ b/docs/system/tls.rst
> @@ -345,6 +345,74 @@ example with VNC:
>
> .. _tls_005fpsk:
>
> +TLS certificates for Post-Quantum Cryptography
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +
> +Given a new enough gnutls release, suitably integrated & configured with
> the
> +operating system crypto policies, QEMU is able to support post-quantum
> +crytography on TLS enabled services, either exclusively or in a hybrid
> mode.
> +
> +In exclusive mode, only a single set of certificates need to be configured
> +for QEMU, with PQC compliant algorithms. Such a QEMU configuration will
> only
> +be able to interoperate with other services (including other QEMU's) that
> +also have PQC enabled. This can result in compatibility concerns during
> the
> +period of transition over to PQC compliant algorithms.
> +
> +In hybrid mode, multiple sets of certificates need to be configured for
> QEMU,
> +at least one set with traditional (non-PQC compliant) algorithms, and at
> least
> +one other set with modern (PQC compliant) algorithms. At time of the TLS
> +handshake, the GNUTLS algorithm priorities should ensure that PQC
> compliant
> +algorithms are negotiated if both sides of the connection support PQC. If
> one
> +side lacks PQC, the TLS handshake should fallback to the non-PQC
> algorithms.
> +This can assist with interoperability during the transition to PQC, but
> has a
> +potential weakness wrt downgrade attacks forcing use of non-PQC
> algorithms.
> +Exclusive PQC mode should be preferred where both peers in the TLS
> connections
> +are known to support PQC.
> +
> +Key generation parameters
> +^^^^^^^^^^^^^^^^^^^^^^^^^
> +
> +To create certificates with PQC compliant algorithms, the ``--key-type``
> +argument must be passed to ``certtool`` when creating private keys. No
> +extra arguments are required for the other ``certtool`` commands, as
> +their behaviour will be determined by the private key type.
> +
> +The typical PQC compliant algorithms to use are ``ML-DSA-44``,
> ``ML-DSA-65``
> +and ``ML-DSA-87``, with ``ML-DSA-65`` being a suitable default choice in
> +the absence of explicit requirements.
> +
> +Taking the example earlier, for creating a key for a client certificate,
> +to use ``ML-DSA-65`` the command line would be modified to look like::
> +
> + # certtool --generate-privkey --key-type=mldsa65 >
> client-hostNNN-key.pem
> +
> +The equivalent modification applies to the creation of the private keys
> +used for server certs, or root/intermediate CA certs.
> +
> +For hybrid mode, the additional indexed certificate naming must be used.
> +If multiple configured certificates are compatible with the mutually
> +supported crypto algorithms between the client and server, then the
> +first matching certificate will be used.
> +
> +IOW, to ensure that PQC certificates are preferred, they must use a
> +non-index based filename, or use an index that is smaller than any
> +non-PQC certificates. ie, ``server-cert.pem`` for PQC and
> ``server-cert-0.pem``
> +for non-PQC, or ``server-cert-0.pem`` for PQC and ``server-cert-1.pem``
> for
> +non-PQC.
> +
> +Force disabling PQC via crypto priority
> +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> +
> +In the OS configuration for system crypto algorithm priorities has
> +enabled PQC, this can (optionally) be overriden in QEMU configuration
> +disable use of PQC using the ``priority`` parameter to the
> ``tls-creds-x509``
> +object::
> +
> + NO_MLDSA="-SIGN-ML-DSA-65:-SIGN-ML-DSA-44:-SIGN-ML-DSA-87"
> +
> NO_MLKEM="-GROUP-X25519-MLKEM768:-GROUP-SECP256R1-MLKEM768:-GROUP-SECP384R1-MLKEM1024"
> + # qemu-nbd --object
> tls-creds-x509,id=tls0,endpoint=server,dir=....,priority=@SYSTEM:$NO_MLDSA:$NO_MLKEM
> +
> +
> TLS Pre-Shared Keys (PSK)
> ~~~~~~~~~~~~~~~~~~~~~~~~~
>
> --
> 2.51.1
>
>