Passwordless SSH Server on macOS

How to disable ssh password authentication and enable private key authentication

One time I need to add access my MacBook Pro remotely using ssh from a Windows 10 machine. It’s very easy actually to enable ssh server on macOS. You just need to open System Preferences → Sharing → check Remote Login and that’s it. Simply connect it using your client machine with ssh username@ip-address.

The problem is, by default this ssh server only accept password login.

To enable passwordless login using private key authentication, we need to configure further. Open your favorite terminal application on your macOS. Edit sshd_config file using your favorite text editor. The file is located at /etc/ssh/sshd_config. Since it requires admin credential, you need to edit it using sudo. Here is an example using vim editor.

sudo -E vim /etc/ssh/sshd_config

Edit only two properties: PasswordAuthentication and ChallengeResponseAuthentication. Set them both to no.

PasswordAuthentication no
ChallengeResponseAuthentication no

Create authorized_keys file if you don’t have one.

touch ~/.ssh/authorized_keys

Enter your other machines’ public key in authorized_keys file.

Recheck Remote Login configuration again to restart ssh server on your macOS. Now try again login via ssh. This time it won’t ask you for password.

Here is the complete sshd_config file on my macOS in case you want to compare it with yours.

#	$OpenBSD: sshd_config,v 1.103 2018/04/09 20:41:22 tj Exp $

# This is the sshd server system-wide configuration file.  See
# sshd_config(5) for more information.

# This sshd was compiled with PATH=/usr/bin:/bin:/usr/sbin:/sbin

# The strategy used for options in the default sshd_config shipped with
# OpenSSH is to specify options with their default value where
# possible, but leave them commented.  Uncommented options override the
# default value.

#Port 22
#AddressFamily any
#ListenAddress 0.0.0.0
#ListenAddress ::

#HostKey /etc/ssh/ssh_host_rsa_key

#HostKey /etc/ssh/ssh_host_ecdsa_key
#HostKey /etc/ssh/ssh_host_ed25519_key

# Ciphers and keying
#RekeyLimit default none

# Logging
#SyslogFacility AUTH
#LogLevel INFO

# Authentication:

#LoginGraceTime 2m
#PermitRootLogin prohibit-password
#StrictModes yes
#MaxAuthTries 6
#MaxSessions 10

#PubkeyAuthentication yes

# The default is to check both .ssh/authorized_keys and .ssh/authorized_keys2
# but this is overridden so installations will only check .ssh/authorized_keys
AuthorizedKeysFile	.ssh/authorized_keys

#AuthorizedPrincipalsFile none

#AuthorizedKeysCommand none
#AuthorizedKeysCommandUser nobody

# For this to work you will also need host keys in /etc/ssh/ssh_known_hosts
#HostbasedAuthentication no
# Change to yes if you don't trust ~/.ssh/known_hosts for
# HostbasedAuthentication
#IgnoreUserKnownHosts no
# Don't read the user's ~/.rhosts and ~/.shosts files
#IgnoreRhosts yes

# To disable tunneled clear text passwords, change to no here!
PasswordAuthentication no
#PasswordAuthentication yes
#PermitEmptyPasswords no

# Change to no to disable s/key passwords
ChallengeResponseAuthentication no
#ChallengeResponseAuthentication yes

# Kerberos options
#KerberosAuthentication no
#KerberosOrLocalPasswd yes
#KerberosTicketCleanup yes
#KerberosGetAFSToken no

# GSSAPI options
#GSSAPIAuthentication no
#GSSAPICleanupCredentials yes

# Set this to 'yes' to enable PAM authentication, account processing,
# and session processing. If this is enabled, PAM authentication will
# be allowed through the ChallengeResponseAuthentication and
# PasswordAuthentication.  Depending on your PAM configuration,
# PAM authentication via ChallengeResponseAuthentication may bypass
# the setting of "PermitRootLogin without-password".
# If you just want the PAM account and session checks to run without
# PAM authentication, then enable this but set PasswordAuthentication
# and ChallengeResponseAuthentication to 'no'.
UsePAM yes

#AllowAgentForwarding yes
#AllowTcpForwarding yes
#GatewayPorts no
X11Forwarding yes
#X11Forwarding no
#X11DisplayOffset 10
#X11UseLocalhost yes
#PermitTTY yes
#PrintMotd yes
#PrintLastLog yes
#TCPKeepAlive yes
#PermitUserEnvironment no
#Compression delayed
#ClientAliveInterval 0
#ClientAliveCountMax 3
#UseDNS no
#PidFile /var/run/sshd.pid
#MaxStartups 10:30:100
#PermitTunnel no
#ChrootDirectory none
#VersionAddendum none

# pass locale information
AcceptEnv LANG LC_*

# no default banner path
#Banner none

# override default of no subsystems
Subsystem	sftp	/usr/libexec/sftp-server

# Example of overriding settings on a per-user basis
#Match User anoncvs
#	X11Forwarding no
#	AllowTcpForwarding no
#	PermitTTY no
#	ForceCommand cvs server

Thanks for reading, see you on my next tutorial.

Cover Photo by Lewis Ngugi on Unsplash

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