[ReK_]

You're thinking of SSH keys, which are not certificates. SSH certificates are indeed x.509: https://datatracker.ietf.org/doc/html/rfc6187

[adontz]

No, I'm thinking of SSH certificates.

Here is the description of file format, it's nothing like x509

https://github.com/openssh/openssh-portable/blob/master/PROT...