From: Daniel P. Berrangé <berrange@redhat.com> This describes the new index based certificate naming scheme, and how to create & deploy certificates for post-quantum cryptography. Signed-off-by: Daniel P. Berrangé <berrange@redhat.com> --- docs/kbase/tlscerts.rst | 88 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 88 insertions(+) diff --git a/docs/kbase/tlscerts.rst b/docs/kbase/tlscerts.rst index c10ab11b7f..db962d0f46 100644 --- a/docs/kbase/tlscerts.rst +++ b/docs/kbase/tlscerts.rst @@ -75,6 +75,25 @@ in the path specified, otherwise the connection will fail with a fatal error. If - For the root user, the global default locations will always be used. +Multiple parallel certificate identities +---------------------------------------- + +Any scenario that requires a certificate identify (``servercert.pem`` / +``serverkey.pem`` and ``clientcert.pem`` / ``clientkey.pem``) can optionally +provide multiple parallel identities via a new indexed file naming +scheme. The new filenames are ``servercertNN.pem`` / ``serverkeyNN.pem`` +and ``clientcertNN.pem`` / ``clientkeyNN.pem``, for values of ``NN`` between +0 and 3 inclusive. + +The new naming can be used instead of the old naming, or concurrently +with the old naming. The old file names will be loaded first (if +present), followed by the indexed file names. Loading will stop at +the first missing index value. ie if ``servercert1.pem`` is not present, +then no attempt will be made to load ``servercert2.pem`` or ``servercert3.pem``. + +If multiple CA certificates are required they must all be concatenated +into the single ``cacert.pem`` file. + Background to TLS certificates ------------------------------ @@ -326,6 +345,75 @@ briefly cover the steps. cp clientkey.pem /etc/pki/libvirt/private/clientkey.pem cp clientcert.pem /etc/pki/libvirt/clientcert.pem +Configuring for Post-Quantum Cryptography +----------------------------------------- + +Given a new enough gnutls release, suitably integrated & configured with the +operating system crypto policies, libvirt 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 libvirt, with PQC compliant algorithms. Such a libvirt configuration will +only be able to interoperate with other libvirt daemons 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 libvirt, +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 > clientkey.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, ``servercert.pem`` for PQC and ``servercert0.pem`` +for non-PQC, or ``servercert0.pem`` for PQC and ``servercert1.pem`` for +non-PQC. + +Force disabling PQC via crypto priority +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +If the OS configuration for system crypto algorithm priorities has +enabled PQC, this can (optionally) be overriden in libvirt server +configuration. To disable use of PQC set the ``tls_priority`` +parameter in the ``libvirtd.conf`` / ``virtproxyd.conf`` files: + + tls_priority = "@SYSTEM:-SIGN-ML-DSA-65:-SIGN-ML-DSA-44:-SIGN-ML-DSA-87:-GROUP-X25519-MLKEM768:-GROUP-SECP256R1-MLKEM768:-GROUP-SECP384R1-MLKEM1024" + +On the client side this can be overriden using the ``tls_priority`` +URI parameter in the libvirt connection address. + + Troubleshooting TLS certificate problems ---------------------------------------- -- 2.51.1