Dropbox 10 – Dropbox Server (SSH)

First we create root’s keys.

Note: We have to leave the passphrase blank as we will be using the keys to auto-authenticate to the Dropbox Relay when creating our SSH tunnels.

ssh-keygen -t rsa

Override the default /root/.ssh/id_rsa with /root/.ssh/dbox-01.id_rsa or something similar. Just use the same naming convention throughout. Each Dropbox Server you deploy will have a unique key identifier.

The output should look something like the following.

Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa): /root/.ssh/dbox-01.id_rsa
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /root/.ssh/dbox-01.id_rsa.
Your public key has been saved in /root/.ssh/dbox-01.id_rsa.pub.
The key fingerprint is:
SHA256:ElmBhJko2aCYALXjvuqzf1Qf+up+3hiFOhdeUlQ//Wg root@dbox-01
The key's randomart image is:
+---[RSA 2048]----+
|==.. =..o. ... |
|*.o.+ .o . . .|
|+.o o . o.|
| . . o .o .o|
| . o S+.o E .|
| . . oo.= . |
| . . o.+ |
| . . . oo+ |
|o+=.. o++o . |

Now setup the SSH server itself.

First, remove default created keys.

mkdir /etc/ssh/oldkeys
mv /etc/ssh/ssh_host* /etc/ssh/oldkeys/

We tweak the SSH configuration file to remove some weak protocols, require key authentication for root, and listen only on localhost.

vi/vim/nano /etc/ssh/sshd_config

# Package generated configuration file
# See the sshd_config(5) manpage for details

# What ports, IPs and protocols we listen for
Port 22
# Use these options to restrict which interfaces/protocols sshd will bind to
#ListenAddress ::
Protocol 2
# HostKeys for protocol version 2
HostKey /etc/ssh/ssh_host_rsa_key
#HostKey /etc/ssh/ssh_host_dsa_key
#HostKey /etc/ssh/ssh_host_ecdsa_key
#HostKey /etc/ssh/ssh_host_ed25519_key
#Privilege Separation is turned on for security
UsePrivilegeSeparation yes

# Lifetime and size of ephemeral version 1 server key
KeyRegenerationInterval 3600
#ServerKeyBits 1024

# Logging
SyslogFacility AUTH
LogLevel INFO

# Authentication:
LoginGraceTime 120
PermitRootLogin prohibit-password
StrictModes yes

RSAAuthentication yes
PubkeyAuthentication yes
#AuthorizedKeysFile %h/.ssh/authorized_keys

# Don't read the user's ~/.rhosts and ~/.shosts files
IgnoreRhosts yes
# For this to work you will also need host keys in /etc/ssh_known_hosts
RhostsRSAAuthentication no
# similar for protocol version 2
HostbasedAuthentication no
# Uncomment if you don't trust ~/.ssh/known_hosts for RhostsRSAAuthentication
#IgnoreUserKnownHosts yes

# To enable empty passwords, change to yes (NOT RECOMMENDED)
PermitEmptyPasswords no

# Change to yes to enable challenge-response passwords (beware issues with
# some PAM modules and threads)
ChallengeResponseAuthentication no

# Change to no to disable tunnelled clear text passwords
PasswordAuthentication no

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

# GSSAPI options
#GSSAPIAuthentication no
#GSSAPICleanupCredentials yes

X11Forwarding yes
X11DisplayOffset 10
PrintMotd no
PrintLastLog yes
TCPKeepAlive yes
#UseLogin no

#MaxStartups 10:30:60
#Banner /etc/issue.net

# Allow client to pass locale environment variables
AcceptEnv LANG LC_*

Subsystem sftp /usr/lib/openssh/sftp-server

# 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

Reconfigure the SSH server to generate new keys.

dpkg-reconfigure openssh-server

Make sure SSH is configured to autostart

systemctl enable ssh


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