Cyber Security

SSH - Common Commands & Secure Config - Cheat Sheet

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Mosabbir Masud

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SSH - Common Commands & Secure Config - Cheat Sheet

Secure Shell is a protocol that provides authentication, encryption and data integrity to secure network communications.

Implementations of Secure Shell offer the following capabilities: a secure command-shell, secure file transfer, and remote access to a variety of TCP/IP applications via a secure tunnel.

Secure Shell client and server applications are widely available for most popular operating systems. 

Functionality of Secure Shell

Secure Shell provides three main capabilities, which open the door for many creative secure solutions. 

  • Secure command-shell

  • Secure file transfer

  • Port forwarding 

Secure Command

Shell Command shells such as those available in Linux, Unix, Windows, or the familiar DOS prompt provide the ability to execute programs and other commands, usually with character output.

A secure command-shell or remote logon allows you to edit files, view the contents of directories and access custom database applications.

Systems and network administrators can remotely start batch jobs, start, view or stop services and processes, create user accounts, change permissions to files and directories and more.

Anything that can be accomplished at a machine’s command prompt can now be done securely from the road or home. 

SSH connections

connects to a server (default port 22)

$ ssh user@server

uses a specific port declared in sshd_config

$ ssh user@server -p other_port

runs a script on a remote server

$ ssh user@server script_to_run

compresses and downloads from a remote server

$ ssh user@server "tar cvzf - ~/source" > output.tgz

specifies other ssh key for connection

$ ssh -i ~/.ssh/specific_ssh_fkey

SSH config

opens config file (usual location)

$ sudo nano /etc/ssh/sshd_config

Changes default SSH port (22)

Port 9809

Disables root login

PermitRootLogin no

restricts access to specific  users

AllowUsers user1, user2

enables login through ssh key

PubkeyAuthentication yes

disables login through password

PasswordAuthentication no

disables usage of files .rhosts and .shosts

IgnoreRhosts yes

disables a less secure type of login

HostbasedAuthentication no

number of unauthenticated connections before dropping

MaxStartups 10:30:100

 No of failed tries before the servers stops accepting new tries

MaxAuthTries 3

max current ssh sessions

MaxSessions 1

disables interactive password authentication

ChallengeResponseAuthentication no

no empty password allowed

PermitEmptyPasswords no

disables Rhost authtentication

RhostsAuthentication no

disables port forwarding (blocks i.e MySQL Workbench)

AllowTcpForwarding no

X11Forwarding no

SCP (Secure Copy)

copies a file from a remote server to a local machine

$ scp user@server:/directory/file.ext local_destination/

copies a file between two servers

$ scp user@server:/dir/file.ext user@server:/dir

copies a file from a local machine to a remote server

$ scp local_destination/file.ext user@server:/directory

uses a specific port declared for SHH in sshd_config

$ scp -P port

coppies recursive a whole folder

$ scp -r user@server:/directory local_destination/

copies all files from a folder

$ scp user@server:/directory/* local_destination/

copies all files from a server folder to the current folder

$ scp user@server:/directory/* .

compresses data on network using gzip

$ scp -C

SSH Service

starts ssh service

$ (sudo) service ssh start

checks ssh service status

$ (sudo) service ssh status

stops ssh service

$ (sudo) service ssh stop

restarts ssh service

$ (sudo) service ssh restart

prints verbose info about the current transfer

$ scp -v

SSH keys

generates a new ssh key

$ ssh-keygen -t rsa -b 4096

sends the key to the server

$ ssh-copy-id user@server

converts ids_rsa into ppk

$ puttygen current_key -o keyname.ppk

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