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I have trouble setting passwordless authentication on a host:

Sep 21 09:57:36 pvestorage2 sshd[1688625]: userauth_pubkey: key type ecdsa-sha2-nistp521 not in PubkeyAcceptedAlgorithms [preauth]
  • OS: Ubuntu 22.04.1 LTS
  • ssh server version: openssh-server 8.9p1-3
  • client: Win10 + putty 0.77 and 0.79 on two systems
  • key: generated with puttygen bundled with version 0.77

I am aware of putty bug related to supplying keys and I have PuTTy updated. I am also aware of ssh-rsa deprecation, this is why I am using this key in the first place.

~$ ssh -Q PubkeyAcceptedAlgorithms | grep nistp521
ecdsa-sha2-nistp521
[email protected]

I have added:

PubkeyAcceptedKeyTypes +ecdsa-sha2-nistp521

to sshd_config in case it changes something.

I am not in liberty to reboot the remote machine for several weeks, only to restart sshd.

I kind of have no idea how to make it work. What did I miss?

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  • Did you generate such a key at the server, too? // Did you assure the private key's access rights "not read/writeable by group or world"? // Did you configure the keyfile in the sshd_config by an entry HostKey /etc/ssh/ssh_host_ecdsa-sha2-nistp521_key? // Just restarting the sshd should be fine to get the new sshd_config re-read. Commented Sep 21, 2023 at 12:34
  • >> Did you generate such a key at the server, too? // No. I generated the key using puttygen and copied over to Ubuntu host. >> Did you assure the private key's access rights "not read/writeable by group or world"? // You mean authorized_keys file? Yes. >> Did you configure the keyfile in the sshd_config by an entry HostKey /etc/ssh/ssh_host_ecdsa-sha2-nistp521_key? // No, I didn't. Why would I? Never did it anywhere and never had any problems. >> Just restarting the sshd should be fine to get the new sshd_config re-read. // Thank you. Commented Sep 22, 2023 at 21:54

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