On Tue, Jul 28, 2026 at 12:05:18PM +0100, xnox wrote:
OpenSSH upstream added a new hybrid hostkey type
ssh_host_mldsa44_ed25519_key.pub.
It is enabled by default, and can be created with ssh-keygen -A.
The openssh-server postinst script however doesn't use ssh-keygen -A and
instead only generates hostkeys of known types and the ones that are configured
in the sshd config.
It appears that it currently doesn't know about mldsa44_ed25519 host key type,
please add support for this new host key type.
The upstream changelog doesn't suggest to me that it's ready to be
enabled yet:
* All: add experimental support for a composite post-quantum
signature scheme that combines ML-DSA 44 and Ed25519 as specified
in draft-miller-sshm-mldsa44-ed25519-composite-sigs.
This scheme is not enabled by default. To use it, you'll need
to add it to HostKeyAlgorithms, PubkeyAcceptedAlgorithms, etc.
Keys may be generated using "ssh-keygen -t mldsa44-ed25519".
Yes, it's enabled by default _specifically in ssh-keygen -A_, but it's
not enabled by default in the rest of OpenSSH, so I think it's too early
at this point. I'll wait until upstream declares it to be
non-experimental.
Thanks,
--
Colin Watson (he/him) [[email protected]]
