I was following this guide to set up SSH authentication with keys, but after following all the steps if I try to login the server still asks for my password.
So I went to check /etc/ssh/sshd_config as the guide recommends, and these two:
PubkeyAuthentication yes RSAAuthentication yes Were commented out, so I enabled them.
Unfortunately the login still didn't work and when checking sudo tail -f /var/log/auth.log I just got:
rexec line 38: Deprecated option RSAAuthentication Is there an up-to-date guide on how to login via SSH with a key?
These are my sshd_config settings
Version:
lsb_release -a No LSB modules are available. Distributor ID: Ubuntu Description: Ubuntu 18.04.1 LTS Release: 18.04 Codename: bionic Current Open ssh version
ssh -V OpenSSH_7.6p1 Ubuntu-4ubuntu0.3, OpenSSL 1.0.2n 7 Dec 2017 ssh -vvvv output
OpenSSH_8.2p1 Ubuntu-4, OpenSSL 1.1.1f 31 Mar 2020 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: resolving "mysite.com" port 22 debug2: ssh_connect_direct debug1: Connecting to mysite.com [ip address] port 22. debug1: Connection established. debug1: identity file /home/user/.ssh/id_rsa type 0 debug1: identity file /home/user/.ssh/id_rsa-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: 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 -1 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: Local version string SSH-2.0-OpenSSH_8.2p1 Ubuntu-4 debug1: Remote protocol version 2.0, remote software version OpenSSH_7.6p1 Ubuntu-4ubuntu0.3 debug1: match: OpenSSH_7.6p1 Ubuntu-4ubuntu0.3 pat OpenSSH_7.0*,OpenSSH_7.1*,OpenSSH_7.2*,OpenSSH_7.3*,OpenSSH_7.4*,OpenSSH_7.5*,OpenSSH_7.6*,OpenSSH_7.7* compat 0x04000002 debug2: fd 3 setting O_NONBLOCK debug1: Authenticating to mysite.com:22 as 'user' debug3: hostkeys_foreach: reading file "/home/user/.ssh/known_hosts" debug3: record_hostkey: found key type ECDSA in file /home/user/.ssh/known_hosts:5 debug3: load_hostkeys: loaded 1 keys from mysite.com debug3: order_hostkeyalgs: prefer hostkeyalgs: ,,,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521 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,,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: ,,,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,,,,,,,,ssh-ed25519,,rsa-sha2-512,rsa-sha2-256,ssh-rsa debug2: ciphers ctos: ,aes128-ctr,aes192-ctr,aes256-ctr,, debug2: ciphers stoc: ,aes128-ctr,aes192-ctr,aes256-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 debug2: compression stoc: none,,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,,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: ssh-rsa,rsa-sha2-512,rsa-sha2-256,ecdsa-sha2-nistp256,ssh-ed25519 debug2: ciphers ctos: ,aes128-ctr,aes192-ctr,aes256-ctr,, debug2: ciphers stoc: ,aes128-ctr,aes192-ctr,aes256-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, debug2: compression stoc: none, debug2: languages ctos: debug2: languages stoc: debug2: first_kex_follows 0 debug2: reserved 0 debug1: kex: algorithm: curve25519-sha256 debug1: kex: host key algorithm: ecdsa-sha2-nistp256 debug1: kex: server->client cipher: MAC: <implicit> compression: none debug1: kex: client->server cipher: MAC: <implicit> compression: none debug3: send packet: type 30 debug1: expecting SSH2_MSG_KEX_ECDH_REPLY debug3: receive packet: type 31 debug1: Server host key: ecdsa-sha2-nistp256 SHA256:[redacted] debug3: hostkeys_foreach: reading file "/home/user/.ssh/known_hosts" debug3: record_hostkey: found key type ECDSA in file /home/user/.ssh/known_hosts:5 debug3: load_hostkeys: loaded 1 keys from mysite.com debug3: hostkeys_foreach: reading file "/home/user/.ssh/known_hosts" debug3: record_hostkey: found key type ECDSA in file /home/user/.ssh/known_hosts:6 debug3: load_hostkeys: loaded 1 keys from ip address debug1: Host 'mysite.com' is known and matches the ECDSA host key. debug1: Found key in /home/user/.ssh/known_hosts:5 debug3: send packet: type 21 debug2: 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: SSH2_MSG_NEWKEYS received debug2: set_newkeys: mode 0 debug1: rekey in after 134217728 blocks debug1: Will attempt key: /home/user/.ssh/id_rsa RSA SHA256:[redacted] debug1: Will attempt key: /home/user/.ssh/id_dsa 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 debug1: Will attempt key: /home/user/.ssh/id_ed25519_sk debug1: Will attempt key: /home/user/.ssh/id_xmss 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,password debug3: start over, passed a different list publickey,password 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: /home/user/.ssh/id_rsa RSA SHA256:[redacted] 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,password debug1: Trying private key: /home/user/.ssh/id_dsa debug3: no such identity: /home/user/.ssh/id_dsa: No such file or directory debug1: Trying private key: /home/user/.ssh/id_ecdsa debug3: no such identity: /home/user/.ssh/id_ecdsa: No such file or directory debug1: Trying private key: /home/user/.ssh/id_ecdsa_sk debug3: no such identity: /home/user/.ssh/id_ecdsa_sk: No such file or directory debug1: Trying private key: /home/user/.ssh/id_ed25519 debug3: no such identity: /home/user/.ssh/id_ed25519: No such file or directory debug1: Trying private key: /home/user/.ssh/id_ed25519_sk debug3: no such identity: /home/user/.ssh/id_ed25519_sk: No such file or directory debug1: Trying private key: /home/user/.ssh/id_xmss debug3: no such identity: /home/user/.ssh/id_xmss: No such file or directory debug2: we did not send a packet, disable method debug3: authmethod_lookup password debug3: remaining preferred: ,password debug3: authmethod_is_enabled password debug1: Next authentication method: password 2 Answers
This has to do with RSA deprecation due to it becoming hackable by hardware that can be purchased under $50,000 USD...
The fix, for me, was.. on the client side, make sure you have a key that the server accepts, like ~/.ssh/id_ecdsa.pub .. if you only see id_rsa.pub, do this on the client side:
ssh-keygen -t ecdsa ..and then:
ssh-copy-id Enter the password for your user to copy the new ecdsa id to the server.. Now this should work without password:
ssh If that doesn't work, some troubleshooting tips:
Client:
ssh-keygen --help usage: ssh-keygen [-q] [-b bits] [-t dsa | ecdsa | ed25519 | rsa | rsa1] ... ..above shows what types of keys (dsa, ecdsa, ed25519) your client can generate.
Server:
Check /etc/ssh/sshd_config for "HostKey" lines:
#HostKey /etc/ssh/ssh_host_rsa_key #HostKey /etc/ssh/ssh_host_ecdsa_key #HostKey /etc/ssh/ssh_host_ed25519_key ..even though they're commented, the sshd_config default is to show defaults in comments. Mine clearly shows rsa as a default, but once rsa has been deprecated, it might not work even with the host key enabled..
Client:
ssh -vvvvv (look at the output, and determine what types of encryption keys are being used / what is failing)
More info can be learned from this excellent writeup:
Try the below guide if the following does not work, you need set no to using a password to only use a pubKEY which is:
nano /etc/ssh/sshd_config Find the following lines and change the value to “no”:
PasswordAuthentication no ChallengeResponseAuthentication no UsePAM no Save and close the file, then restart SSH service to apply the configuration:
systemctl restart ssh The idea is you set password to no while setting yes to keys therfore SSH will always use keys and never ask for a password, it cannot do both at the same time and if both are set then it will always ask for the password and ignore keys.
Guide to try if above does not work:
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