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dust_bg
Asked: 2024-10-14 01:23:25 +0800 CST

SSH client does not offer public key to SSH server

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I can't connect to my Ubuntu 22.04 server via SSH from exactly one host. I can connect to that server from other hosts with no problems. But, when I try to connect from that host with: ssh -p 5435 -i ~/.ssh/id_ed25519 user@my_server.com -vvv I'm getting:

OpenSSH_8.9p1 Ubuntu-3ubuntu0.10, OpenSSL 3.0.2 15 Mar 2022
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: include /etc/ssh/ssh_config.d/*.conf matched no files
debug1: /etc/ssh/ssh_config line 21: Applying options for *
debug3: expanded UserKnownHostsFile '~/.ssh/known_hosts' -> '/home/user/.ssh/known_hosts'
debug3: expanded UserKnownHostsFile '~/.ssh/known_hosts2' -> '/home/user/.ssh/known_hosts2'
debug2: resolving "my_server.com" port 5435
debug3: resolve_host: lookup my_server.com: 5435
debug3: ssh_connect_direct: entering
debug1: Connecting to my_server.com [xxx.xxx.xxx.xxx] port 5435.
debug3: set_sock_tos: set socket 3 IP_TOS 0x10
debug1: Connection established.
debug1: identity file /home/user/.ssh/id_rsa type -1
debug1: identity file /home/user/.ssh/id_rsa-cert type -1
debug1: identity file /home/user/.ssh/id_ecdsa type -1
debug1: identity file /home/user/.ssh/id_ecdsa-cert type -1
debug1: identity file /home/user/.ssh/id_ecdsa_sk type -1
debug1: identity file /home/user/.ssh/id_ecdsa_sk-cert type -1
debug1: identity file /home/user/.ssh/id_ed25519 type 3
debug1: identity file /home/user/.ssh/id_ed25519-cert type -1
debug1: identity file /home/user/.ssh/id_ed25519_sk type -1
debug1: identity file /home/user/.ssh/id_ed25519_sk-cert type -1
debug1: identity file /home/user/.ssh/id_xmss type -1
debug1: identity file /home/user/.ssh/id_xmss-cert type -1
debug1: identity file /home/user/.ssh/id_dsa type -1
debug1: identity file /home/user/.ssh/id_dsa-cert type -1
debug1: Local version string SSH-2.0-OpenSSH_8.9p1 Ubuntu-3ubuntu0.10
debug1: Remote protocol version 2.0, remote software version OpenSSH_8.9p1 Ubuntu-3ubuntu0.10
debug1: compat_banner: match: OpenSSH_8.9p1 Ubuntu-3ubuntu0.10 pat OpenSSH* compat 0x04000000
debug2: fd 3 setting O_NONBLOCK
debug1: Authenticating to my_server.com:5435 as 'user'
debug3: put_host_port: [my_server.com]:5435
debug3: record_hostkey: found key type ED25519 in file /home/user/.ssh/known_hosts:1
debug3: load_hostkeys_file: loaded 1 keys from [my_server.com]:5435
debug1: load_hostkeys: fopen /home/user/.ssh/known_hosts2: No such file or directory
debug1: load_hostkeys: fopen /etc/ssh/ssh_known_hosts: No such file or directory
debug1: load_hostkeys: fopen /etc/ssh/ssh_known_hosts2: No such file or directory
debug3: order_hostkeyalgs: have matching best-preference key type [email protected], using HostkeyAlgorithms verbatim
debug3: send packet: type 20
debug1: SSH2_MSG_KEXINIT sent
debug3: receive packet: type 20
debug1: SSH2_MSG_KEXINIT received
debug2: local client KEXINIT proposal
debug2: KEX algorithms: curve25519-sha256,[email protected],ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,[email protected],diffie-hellman-group-exchange-sha256,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,diffie-hellman-group14-sha256,ext-info-c,[email protected]
debug2: host key algorithms: [email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],ssh-ed25519,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,[email protected],[email protected],rsa-sha2-512,rsa-sha2-256
debug2: ciphers ctos: [email protected],aes128-ctr,aes192-ctr,aes256-ctr,[email protected],[email protected]
debug2: ciphers stoc: [email protected],aes128-ctr,aes192-ctr,aes256-ctr,[email protected],[email protected]
debug2: MACs ctos: [email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],hmac-sha2-256,hmac-sha2-512,hmac-sha1
debug2: MACs stoc: [email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],hmac-sha2-256,hmac-sha2-512,hmac-sha1
debug2: compression ctos: none,[email protected],zlib
debug2: compression stoc: none,[email protected],zlib
debug2: languages ctos:
debug2: languages stoc:
debug2: first_kex_follows 0
debug2: reserved 0
debug2: peer server KEXINIT proposal
debug2: KEX algorithms: curve25519-sha256,[email protected],ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,[email protected],diffie-hellman-group-exchange-sha256,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,diffie-hellman-group14-sha256,[email protected]
debug2: host key algorithms: rsa-sha2-512,rsa-sha2-256,ssh-rsa,ecdsa-sha2-nistp256,ssh-ed25519
debug2: ciphers ctos: [email protected],aes128-ctr,aes192-ctr,aes256-ctr,[email protected],[email protected]
debug2: ciphers stoc: [email protected],aes128-ctr,aes192-ctr,aes256-ctr,[email protected],[email protected]
debug2: MACs ctos: [email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],hmac-sha2-256,hmac-sha2-512,hmac-sha1
debug2: MACs stoc: [email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],hmac-sha2-256,hmac-sha2-512,hmac-sha1
debug2: compression ctos: none,[email protected]
debug2: compression stoc: none,[email protected]
debug2: languages ctos:
debug2: languages stoc:
debug2: first_kex_follows 0
debug2: reserved 0
debug3: kex_choose_conf: will use strict KEX ordering
debug1: kex: algorithm: curve25519-sha256
debug1: kex: host key algorithm: ssh-ed25519
debug1: kex: server->client cipher: [email protected] MAC: <implicit> compression: none
debug1: kex: client->server cipher: [email protected] MAC: <implicit> compression: none
debug3: send packet: type 30
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug3: receive packet: type 31
debug1: SSH2_MSG_KEX_ECDH_REPLY received
debug1: Server host key: ssh-ed25519 SHA256:ChCUrM9ZYCR057q60M84kB6pAQa9bQ8ZEHVuw8g7/p0
debug3: put_host_port: [xxx.xxx.xxx.xxx]:5435
debug3: put_host_port: [my_server.com]:5435
debug3: record_hostkey: found key type ED25519 in file /home/user/.ssh/known_hosts:1
debug3: load_hostkeys_file: loaded 1 keys from [my_server.com]:5435
debug1: load_hostkeys: fopen /home/user/.ssh/known_hosts2: No such file or directory
debug1: load_hostkeys: fopen /etc/ssh/ssh_known_hosts: No such file or directory
debug1: load_hostkeys: fopen /etc/ssh/ssh_known_hosts2: No such file or directory
debug1: Host '[my-server.com]:5435' is known and matches the ED25519 host key.
debug1: Found key in /home/user/.ssh/known_hosts:1
debug3: send packet: type 21
debug1: ssh_packet_send2_wrapped: resetting send seqnr 3
debug2: ssh_set_newkeys: mode 1
debug1: rekey out after 134217728 blocks
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug3: receive packet: type 21
debug1: ssh_packet_read_poll2: resetting read seqnr 3
debug1: SSH2_MSG_NEWKEYS received
debug2: ssh_set_newkeys: mode 0
debug1: rekey in after 134217728 blocks
debug1: Will attempt key: /home/user/.ssh/id_rsa
debug1: Will attempt key: /home/user/.ssh/id_ecdsa
debug1: Will attempt key: /home/user/.ssh/id_ecdsa_sk
debug1: Will attempt key: /home/user/.ssh/id_ed25519 ED25519 SHA256:95gTIyyYHXV+UgGYTJiGgC5ulxp3jQoeHmhohQRbIPI
debug1: Will attempt key: /home/user/.ssh/id_ed25519_sk
debug1: Will attempt key: /home/user/.ssh/id_xmss
debug1: Will attempt key: /home/user/.ssh/id_dsa
debug2: pubkey_prepare: done
debug3: send packet: type 5
debug3: receive packet: type 7
debug1: SSH2_MSG_EXT_INFO received
debug1: kex_input_ext_info: server-sig-algs=<ssh-ed25519,[email protected],ssh-rsa,rsa-sha2-256,rsa-sha2-512,ssh-dss,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,[email protected],[email protected]>
debug1: kex_input_ext_info: [email protected]=<0>
debug3: receive packet: type 6
debug2: service_accept: ssh-userauth
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug3: send packet: type 50
debug3: receive packet: type 51
debug1: Authentications that can continue: publickey
debug3: start over, passed a different list publickey
debug3: preferred gssapi-with-mic,keyboard-interactive,password
debug1: No more authentication methods to try.
[email protected]: Permission denied (publickey).

It seems that the client does not offer any public key to the server. There should be Offering public key:... after Authentications that can continue: publickey

The ~/.ssh folder seems to have the right permissions:

user@client:~$ ll .ssh
total 24
drwx------ 2 user user 4096 Oct 13 18:54 ./
drwxr-xr-x 8 user user 4096 Oct 12 12:13 ../
-rw------- 1 user user   96 Sep 14 16:50 authorized_keys
-rw------- 1 user user  411 Oct 12 11:42 id_ed25519
-rw-r--r-- 1 user user   96 Oct 12 11:42 id_ed25519.pub
-rw-r--r-- 1 user user  142 Oct 12 11:45 known_hosts

Also, I have ed25519 enabled in keys:

$ ssh -Q key

ssh-ed25519
[email protected]
...

I have my public key in the server's authorised_keys file, I checked that carefully with my local id_ed25519.pub. They are the same. In the server's logs, I have:

$ tail -f /var/log/auth.log

Oct 13 19:19:53 my_server sshd[3131]: Connection closed by authenticating user user xxx.xxx.xxx.xxx port 39810 [preauth]

What could be the problem? I reinstalled ssh but it does not help. I also generated and uploaded a new key - same error. Again, I can connect to that server from at least 2 other hosts with the same user.

server

2 Answers

  1. Best Answer

    You may have PubkeyAuthentication set to no somewhere on the client.

    Normally:

    debug3: preferred gssapi-with-mic,keyboard-interactive,password

    should include publickey if PubkeyAuthentication is unset / set to yes:

    Specifies whether to try public key authentication. The argument to this keyword must be yes (the default), no, unbound or host-bound.

    % ssh -vvv -i ~/.ssh/id_rsa_github_personal 192.168.1.253 |& grep 'preferred' 
debug3: preferred gssapi-with-mic,publickey,keyboard-interactive,password

    However, if I override PubkeyAuthentication with no:

    % ssh -vvv -o PubkeyAuthentication=no -i ~/.ssh/id_rsa_github_personal 192.168.1.253 |& grep 'preferred'  
debug3: preferred gssapi-with-mic,keyboard-interactive,password

    Check if you have PubkeyAuthentication set to no in ~/.ssh/config, /etc/ssh/ssh_config or /etc/ssh/ssh_config.d/*:

    grep 'PubkeyAuthentication' ~/.ssh/config /etc/ssh/ssh_config /etc/ssh/ssh_config.d/*
    • 16

  2. There seems to be no pubkey in your preferred authentication methods. Check your ssh config files (/etc/ssh/ssh_config and ~/.ssh/config) if the option PreferredAuthentications is changed somewhere.

    Also, on the server check /etc/ssh/sshd_config if PubkeyAcceptedKeyTypes includes ed25519, and if PubkeyAuthentication is set to yes (it should be according to the log).

    Otherwise you could try a new RSA 4096 key.

    • 3