By beltorak
Hi; I am attempting to follow the tutorial posted here as a guide.
I’ve created three LXC machines to practice with: ssh-ca, ssh-server, and ssh-client.
On ssh-ca I self-signed the “ssh_host_ed25519_key” yielding “ssh_host_ed25519_key-cert.pub”.
I transferred the ssh-server “ssh_host_ed25519_key.pub” to the ssh-ca machine as “server.pub”, signed it with the ssh-ca’s “ssh_host_ed25519_key” yielding “server-cert.pub”, and transferred this back to ssh-server as “ssh_host_ed25519_key-cert.pub”. I edited ssh-server’s “sshd_config” to add HostCertificate /etc/ssh/ssh_host_ed25519_key-cert.pub and restarted the ssh-server sshd daemon (service ssh restart).
I transferred the ssh-ca “ssh_host_ed25519_key-cert.pub” to ssh-client and stuck it in ~/.ssh/known_hosts file as (roughly)
@cert-authority * ssh-ed25519-cert-v01@openssh.com AAAAIHN ... QFRDQ== root@trusty-builds
However, attempting to log in from ssh-client to ssh-server (abbreviated ssh -v output):
debug1: Server host key: ED25519-CERT 85:46:34:5f:93:4c:d0:f5:c3:a4:14:87:38:b9:41:7d
debug1: ssh_ed25519_verify: signature correct
debug1: No matching CA found. Retry with plain key
The authenticity of host '10.0.1.222 (10.0.1.222)' can't be established.
ED25519 key fingerprint is 85:46:34:5f:93:4c:d0:f5:c3:a4:14:87:38:b9:41:7d.
Are you sure you want to continue connecting (yes/no)?
What am I doing wrong? Is * a valid hostname wildcard? Is it possible I messed up one of my signing commands? How could I verify that the ssh-server cert is signed by the ssh-ca key?
Thanks
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Accepted Answer
The ssh client tries to validate the hostname given in the certificate the server sent.
The hostname had to be given after the -n switch, when signing the server’s public key.
ssh-keygen -s server_ca -I host_host1 -h -n host1.example.com -V +52w /etc/ssh/ssh_host_rsa_key.pub
If you have forgotten the name, you can also see it in the debug messages when you try to connect to the server via ssh with -vv. (I had the same problem…)
debug1: Server host certificate: ssh-rsa-cert-v01@openssh.com SHA256:...
debug2: Server host certificate hostname: host1.example.com
debug1: No matching CA found. Retry with plain key
The authenticity of host '192.168.33.12 (192.168.33.12)' can't be established.
When trying to connect to the host via IP, one has to give the hostname in the options:
ssh -o HostName=host1.example.com root@192.168.33.12
* is a valid hostname wildcard.
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