Cannot sign certificate with Trezor as SSH CA

[movefasta]

Device: Trezor Model T
OS: NixOS 24.11.20241015.7881fbf (Vicuna)
Versions: trezor-agent=0.12.0, libagent=0.15.0

When i try to sign file it works fine:

> trezor-agent -e ed25519 [email protected] -- ssh-keygen -Y sign -f ~/.ssh/trezor-github.pub -n file README.md        
Signing file README.md
Write signature to README.md.sig
> cat README.md.sig                                                                                                                                                                                                                                               
-----BEGIN SSH SIGNATURE-----
U1NIU0lHAAAAAQAAADMAAAALc3NoLWVkMjU1MTkAAAAgAtOko3bPtNBNxLlyDKYV2MUt00
R5nHcDqYgXKOK7Y6cAAAAEZmlsZQAAAAAAAAAGc2hhNTEyAAAAUwAAAAtzc2gtZWQyNTUx
OQAAAEAw7ANBx73olTBSW0TcbjozUJ8mgOeZuNCnc8wcY60IkeaZi0zXvv3DpIxF2Fd/MO
5UvTSCgAyM+XwzZahWsrIB
-----END SSH SIGNATURE-----

If i try to sign pubkey to create certificate with SSH libagent return EOFError:

trezor-agent -e ed25519 [email protected] -- ssh-keygen -Us ~/.ssh/trezor-github.pub -I 2024_ed25519 2024_ed25519.pub
2024-10-18 13:46:39,513 ERROR        signature with "<ssh://[email protected]|ed25519>" key failed                               [protocol.py:151]
Traceback (most recent call last):
  File "/nix/store/x4dypckndkdvqh3lvfv58wnayj2a0bla-python3.12-libagent-0.15.0/lib/python3.12/site-packages/libagent/ssh/protocol.py", line 147, in sign_message
    signature = self.conn.sign(blob=blob, identity=key['identity'])
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/nix/store/x4dypckndkdvqh3lvfv58wnayj2a0bla-python3.12-libagent-0.15.0/lib/python3.12/site-packages/libagent/ssh/__init__.py", line 279, in sign
    return conn.sign_ssh_challenge(blob=blob, identity=identity)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/nix/store/x4dypckndkdvqh3lvfv58wnayj2a0bla-python3.12-libagent-0.15.0/lib/python3.12/site-packages/libagent/ssh/client.py", line 35, in sign_ssh_challenge
    msg = parse_ssh_blob(blob)
          ^^^^^^^^^^^^^^^^^^^^
  File "/nix/store/x4dypckndkdvqh3lvfv58wnayj2a0bla-python3.12-libagent-0.15.0/lib/python3.12/site-packages/libagent/ssh/client.py", line 71, in parse_ssh_blob
    res['user'] = util.read_frame(i)
                  ^^^^^^^^^^^^^^^^^^
  File "/nix/store/x4dypckndkdvqh3lvfv58wnayj2a0bla-python3.12-libagent-0.15.0/lib/python3.12/site-packages/libagent/util.py", line 53, in read_frame
    return recv(conn, size)
           ^^^^^^^^^^^^^^^^
  File "/nix/store/x4dypckndkdvqh3lvfv58wnayj2a0bla-python3.12-libagent-0.15.0/lib/python3.12/site-packages/libagent/util.py", line 40, in recv
    raise EOFError
EOFError
Couldn't certify 2024_ed25519.pub via agent: communication with agent failed

[romanz]

https://github.com/openssh/openssh-portable/blob/master/PROTOCOL.certkeys
https://en.wikibooks.org/wiki/OpenSSH/Cookbook/Certificate-based_Authentication