SSH Public Key Login mit ed25519 funktioniert nicht

Du möchtest dich per Public Key auf einem Host einloggen und obwohl du alles nach Anleitung umgesetzt und es auch mehrfach geprüft hast, funktioniert die Authentifizierung nicht und du bekommst immer wieder den Passwort-Prompt?

Dann liegt es vllt. daran, dass der SSH-Server den verwendeten ed25519-Key nicht unterstützt.

Das Verbose-Log auf Clientseite könnte für diesen Fall wie folgt aussehen:

ssh -vvv -i ~/.ssh/id_ed25519 root@192.168.0.1

OpenSSH_8.4p1 Debian-5+deb11u1, OpenSSL 1.1.1n  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 *
debug2: resolve_canonicalize: hostname 192.168.0.1 is address
debug3: expanded UserKnownHostsFile '~/.ssh/known_hosts' -> '/root/.ssh/known_hosts'
debug3: expanded UserKnownHostsFile '~/.ssh/known_hosts2' -> '/root/.ssh/known_hosts2'
debug2: ssh_connect_direct
debug1: Connecting to 192.168.0.1 [192.168.0.1] port 22.
debug1: Connection established.
debug1: identity file /root/.ssh/id_ed25519 type 3
debug1: identity file /root/.ssh/id_ed25519-cert type -1
debug1: Local version string SSH-2.0-OpenSSH_8.4p1 Debian-5+deb11u1
debug1: Remote protocol version 2.0, remote software version OpenSSH_7.9
debug1: match: OpenSSH_7.9 pat OpenSSH* compat 0x04000000
debug2: fd 3 setting O_NONBLOCK
debug1: Authenticating to 192.168.0.1:22 as 'root'
debug3: hostkeys_foreach: reading file "/root/.ssh/known_hosts"
debug3: record_hostkey: found key type RSA in file /root/.ssh/known_hosts:3
debug3: load_hostkeys: loaded 1 keys from 192.168.0.1
debug3: order_hostkeyalgs: prefer hostkeyalgs: rsa-sha2-512-cert-v01@openssh.com,rsa-sha2-256-cert-v01@openssh.com,ssh-rsa-cert-v01@openssh.com,rsa-sha2-512,rsa-sha2-256,ssh-rsa
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,curve25519-sha256@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,diffie-hellman-group14-sha256,ext-info-c
debug2: host key algorithms: rsa-sha2-512-cert-v01@openssh.com,rsa-sha2-256-cert-v01@openssh.com,ssh-rsa-cert-v01@openssh.com,rsa-sha2-512,rsa-sha2-256,ssh-rsa,ecdsa-sha2-nistp256-cert-v01@openssh.com,ecdsa-sha2-nistp384-cert-v01@openssh.com,ecdsa-sha2-nistp521-cert-v01@openssh.com,sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,ssh-ed25519-cert-v01@openssh.com,sk-ssh-ed25519-cert-v01@openssh.com,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,sk-ecdsa-sha2-nistp256@openssh.com,ssh-ed25519,sk-ssh-ed25519@openssh.com
debug2: ciphers ctos: chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com
debug2: ciphers stoc: chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com
debug2: MACs ctos: umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-sha1
debug2: MACs stoc: umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-sha1
debug2: compression ctos: none,zlib@openssh.com,zlib
debug2: compression stoc: none,zlib@openssh.com,zlib
debug2: languages ctos: 
debug2: languages stoc: 
debug2: first_kex_follows 0 
debug2: reserved 0 
debug2: peer server KEXINIT proposal
debug2: KEX algorithms: ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,diffie-hellman-group14-sha256,diffie-hellman-group14-sha1
debug2: host key algorithms: rsa-sha2-512,rsa-sha2-256,ssh-rsa
debug2: ciphers ctos: aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes192-ctr,aes128-ctr
debug2: ciphers stoc: aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes192-ctr,aes128-ctr
debug2: MACs ctos: hmac-sha2-256,hmac-sha2-512,hmac-sha1
debug2: MACs stoc: hmac-sha2-256,hmac-sha2-512,hmac-sha1
debug2: compression ctos: none,zlib@openssh.com
debug2: compression stoc: none,zlib@openssh.com
debug2: languages ctos: 
debug2: languages stoc: 
debug2: first_kex_follows 0 
debug2: reserved 0 
debug1: kex: algorithm: ecdh-sha2-nistp256
debug1: kex: host key algorithm: rsa-sha2-512
debug1: kex: server->client cipher: aes128-ctr MAC: hmac-sha2-256 compression: none
debug1: kex: client->server cipher: aes128-ctr MAC: hmac-sha2-256 compression: none
debug3: send packet: type 30
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug3: receive packet: type 31
debug1: Server host key: ssh-rsa SHA256:d4 [...] yI
debug3: hostkeys_foreach: reading file "/root/.ssh/known_hosts"
debug3: record_hostkey: found key type RSA in file /root/.ssh/known_hosts:3
debug3: load_hostkeys: loaded 1 keys from 192.168.0.1
debug1: Host '192.168.0.1' is known and matches the RSA host key.
debug1: Found key in /root/.ssh/known_hosts:3
debug3: send packet: type 21
debug2: set_newkeys: mode 1
debug1: rekey out after 4294967296 blocks
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug3: receive packet: type 21
debug1: SSH2_MSG_NEWKEYS received
debug2: set_newkeys: mode 0
debug1: rekey in after 4294967296 blocks
debug1: Will attempt key: /root/.ssh/id_ed25519 ED25519 SHA256:E2 [...] Nk explicit
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,ssh-rsa,rsa-sha2-256,rsa-sha2-512,ssh-dss,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521>
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,keyboard-interactive
debug3: start over, passed a different list publickey,keyboard-interactive
debug3: preferred gssapi-with-mic,publickey,keyboard-interactive,password
debug3: authmethod_lookup publickey
debug3: remaining preferred: keyboard-interactive,password

debug3: authmethod_is_enabled publickey
debug1: Next authentication method: publickey
debug1: Offering public key: /root/.ssh/id_ed25519 ED25519 SHA256:E2 [...] Nk explicit
debug3: send packet: type 50
debug2: we sent a publickey packet, wait for reply
debug3: receive packet: type 51
debug1: Authentications that can continue: publickey,keyboard-interactive

debug2: we did not send a packet, disable method

debug3: authmethod_lookup keyboard-interactive
debug3: remaining preferred: password
debug3: authmethod_is_enabled keyboard-interactive
debug1: Next authentication method: keyboard-interactive
debug2: userauth_kbdint
debug3: send packet: type 50
debug2: we sent a keyboard-interactive packet, wait for reply
debug3: receive packet: type 60
debug2: input_userauth_info_req
debug2: input_userauth_info_req: num_prompts 1
Password:

Versuche es stattdessen mit einem RSA-Key. Den erstellst du dir wie folgt:

ssh-keygen -t rsa

Um dich dann mit dem Key einzuloggen, musst du ihn explizit angeben:

ssh -i ~/.ssh/id_rsa root@192.168.0.1

Bei einem veralteten Host mit ESXi 6.7 konnte ich dadurch das Login-Problem losen und mich passwortlos anmelden.