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SSH Server

Preparation

Note

Clone terlebih dahulu VM DebianZero menjadi Praktikum SSH Server dan rubah hostname dari VM Praktikum SSH Server Menjadi SSH-Server , setting pula IP Address untuk enp0s8 menjadi 192.168.10.2. Kemudian SSH dari CMD.

Warning

Jika error seperti dibawah ini ketika SSH 

C:\Users\Monk>ssh useradmin@192.168.10.2
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@    WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that a host key has just been changed.
The fingerprint for the ECDSA key sent by the remote host is
SHA256:L/3cnhqkHGYiiyFzDHwFeR2HOIfb4azsKi1UCtBFl4Y.
Please contact your system administrator.
Add correct host key in C:\\Users\\Monk/.ssh/known_hosts to get rid of this message.
Offending ECDSA key in C:\\Users\\Monk/.ssh/known_hosts:1
Host key for 192.168.10.2 has changed and you have requested strict checking.
Host key verification failed.
Gunakan perintah dibawah ini, namun sesuaikan Ip Address dan Path known_hosts kalian.
C:\Users\Monk>ssh-keygen -R 192.168.10.2 -f C:\\Users\\Monk/.ssh/known_hosts
Host 192.168.10.2 found: line 1
C:\\Users\\Monk/.ssh/known_hosts updated.
Original contents retained as C:\\Users\\Monk/.ssh/known_hosts.old

Installasi openssh-server

root@debian:~# apt-get install openssh-server -y

Membuat user sudo

root@debian:~# adduser admin

Memasukkan User admin kedalam group sudo

root@SSH-Server:~# adduser admin sudo
Adding user `admin' to group `sudo' ...
Adding user admin to group sudo
Done.

Warning

apabila sudo command not found install terlebih dahulu sudo dengan apt-get install sudo

Testing

root@SSH-Server:~# su admin
admin@SSH-Server:/root$ apt-get update

Failure

admin@SSH-Server:/root$ apt-get update
Reading package lists... Done
E: Could not open lock file /var/lib/apt/lists/lock - open (13: Permission denied)
E: Unable to lock directory /var/lib/apt/lists/
W: Problem unlinking the file /var/cache/apt/pkgcache.bin - RemoveCaches (13: Permission denied)
W: Problem unlinking the file /var/cache/apt/srcpkgcache.bin - RemoveCaches (13: Permission denied)

admin@SSH-Server:/root$ sudo apt-get update

Warning

Apabila muncul error seperti dibawah ini:

sudo: unable to resolve host ssh-server: Name or service not known

Masukkan perintah seperti di bawah ini :

admin@ssh-server:~$ sudo nano /etc/hosts

127.0.0.1       localhost
127.0.1.1       ssh-server

# The following lines are desirable for IPv6 capable hosts
::1     localhost ip6-localhost ip6-loopback
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters

Success

admin@SSH-Server:/root$ sudo apt-get update
sudo: unable to resolve host SSH-Server: No address associated with hostname

We trust you have received the usual lecture from the local System
Administrator. It usually boils down to these three things:

#1) Respect the privacy of others.
#2) Think before you type.
#3) With great power comes great responsibility.

[sudo] password for admin:
Get:1 http://mirror.poliwangi.ac.id/debian bullseye InRelease [116 kB]

Mengamankan SSH

Mengganti Port

admin@SSH-Server:~$ sudo nano /etc/ssh/sshd_config

nano /etc/ssh/sshd_config
Port 26
#AddressFamily any
#ListenAddress 0.0.0.0
#ListenAddress ::

admin@SSH-Server:~$ sudo service sshd restart

Testing

C:\Users\Monk>ssh admin@192.168.10.2 -p 26
admin@192.168.10.2's password:
Linux SSH-Server 5.10.0-18-amd64 #1 SMP Debian 5.10.140-1 (2022-09-02) x86_64
  _____  _______      _______
 |  __ \|  __ \ \    / / ____|
 | |__) | |__) \ \  / / (___
 |  _  /|  ___/ \ \/ / \___ \
 | | \ \| |      \  /  ____) |
 |_|  \_\_|       \/  |_____/



admin@SSH-Server:~$

DIsable root Login SSH

admin@SSH-Server:~$ sudo nano /etc/ssh/sshd_config

nano /etc/ssh/sshd_config
# Authentication:

#LoginGraceTime 2m
PermitRootLogin no
#StrictModes yes
#MaxAuthTries 6
#MaxSessions 10

admin@SSH-Server:~$ sudo service sshd restart

Warning

Dengan konfigurasi diatas kita tidak dapat login menggunakan user root ketika SSH.

Testing

Failure

admin@SSH-Server:~$ exit
logout
Connection to 192.168.10.2 closed.

C:\Users\Monk>ssh root@192.168.10.2 -p 26

Disable root sbin/nologin

admin@debian:~$ sudo nano /etc/passwd
sudo nano /etc/passwd
root:x:0:0:root:/root:/usr/sbin/nologin
daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin
bin:x:2:2:bin:/bin:/usr/sbin/nologin

Failure

admin@debian:~$ su -
Password:
This account is currently not available.

SSH KEY

Membuat Public Key dan Private Key

Perintah ini dilakukan di CMD

CMD
C:\Users\Monk>ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (C:\Users\Monk/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in C:\Users\Monk/.ssh/id_rsa
Your public key has been saved in C:\Users\Monk/.ssh/id_rsa.pub
The key fingerprint is:
SHA256:qhM9dMIhzwQMHrK0Vy/aWncF9OK8E4oM1WCunksSz7o monk@LAPTOP-CPTQFMIT
The key's randomart image is:
+---[RSA 3072]----+
|..oo.=  .o       |
|.+..* *   o      |
|.... X + . o     |
|  . = B + o      |
| . + = +S=       |
|  = B =.o o      |
| . B +.o o       |
|  + o.    .      |
| E....           |
+----[SHA256]-----+

Copy public key ke Server

Perintah ini dijalankan di CMD

CMD
C:\Users\Monk>scp -P 26 .ssh/id_rsa.pub admin@192.168.10.2:/home/admin
admin@192.168.10.2's password:
id_rsa.pub                 100%  575   175.4KB/s   00:00
SSH Kedalam Server Melalui CMD.
CMD
C:\Users\Monk>ssh -p 26 admin@192.168.10.2
Memindahkahkan id_rsa.pub kedalam authorized_key 
admin@SSH-Server:~$ ls
id_rsa.pub
admin@SSH-Server:~$ mkdir .ssh
admin@SSH-Server:~$ cat id_rsa.pub >> .ssh/authorized_keys
SSH kembali menggunakan keys

CMD
admin@SSH-Server:~$ exit
logout
Connection to 192.168.10.2 closed.

Success

CMD
C:\Users\Monk>ssh -p 26 -i .ssh/id_rsa admin@192.168.10.2
Linux SSH-Server 5.10.0-18-amd64 #1 SMP Debian 5.10.140-1 (2022-09-02) x86_64
  _____  _______      _______
 |  __ \|  __ \ \    / / ____|
 | |__) | |__) \ \  / / (___
|  _  /|  ___/ \ \/ / \___ \
 | | \ \| |      \  /  ____) |
|_|  \_\_|       \/  |_____/

Last login: Wed Aug  2 09:24:25 2023 from 192.168.10.101
admin@SSH-Server:~$

Tugas Praktikum !!!

  1. Buatlah sebuah kelompok yang terdiri dari 2 orang.
  2. Konfigurasikan SSH dengan ketentuan berikut :
    • Buatlah User baru dengan nama teman kalian (B) pada server anda (A), dan buatlah user baru dengan nama anda sendiri (A) pada server teman kalian (B).
    • Konfigurasikan agar SI A dapat melakukan SSH KEY ke Server B dan SI B dapat melakukan SSH KEY ke server A.
  3. Dokumentasikan lalu dikumpulkan via discord dengan format NAMA_SI_A-NAMA_SI_B-SSH_Server.doc/pdf