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 yesWere 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 RSAAuthenticationIs 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: bionicCurrent Open ssh version
ssh -V
OpenSSH_7.6p1 Ubuntu-4ubuntu0.3, OpenSSL 1.0.2n 7 Dec 2017ssh -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: password2 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_configFind the following lines and change the value to “no”:
PasswordAuthentication no
ChallengeResponseAuthentication no
UsePAM noSave and close the file, then restart SSH service to apply the configuration:
systemctl restart sshThe 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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