Explain how to alter the certtool commands for creating certficates, so that they can use algorithms that are compliant with post-quantum crytography standards. Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com> Signed-off-by: Daniel P. Berrangé <berrange@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