Securing Raspberry Pi (SSH keys, firewall) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to generate an SSH key pair on Raspberry Pi.

Raspberry Pi

ssh-keygen -t [1] -b 2048 -f ~/.ssh/id_rsa

Drag options to blanks, or click blank then click option'

Aecdsa

Bdsa

Crsa

Ded25519

Attempts:

3 left

💡 Hint

Common Mistakes

Using unsupported or less common key types like dsa.

The rsa algorithm is commonly used for SSH key generation and is widely supported.

2fill in blank

medium

Complete the command to copy your SSH public key to the Raspberry Pi for passwordless login.

Raspberry Pi

ssh-copy-id [1]@raspberrypi.local

Drag options to blanks, or click blank then click option'

Api

Broot

Cadmin

Duser

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'root' or other usernames that may not exist.

The default user on Raspberry Pi OS is pi, so you copy the key to that user.

3fill in blank

hard

Fix the error in the command to enable the UFW firewall on Raspberry Pi.

Raspberry Pi

sudo ufw [1]

Drag options to blanks, or click blank then click option'

Aon

Bactivate

Cstart

Denable

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'start' or 'activate' which are not valid UFW commands.

The correct command to enable UFW is sudo ufw enable.

4fill in blank

hard

Fill both blanks to allow SSH and deny all other incoming connections using UFW.

Raspberry Pi

sudo ufw [1] ssh
sudo ufw [2] incoming

Drag options to blanks, or click blank then click option'

Aallow

Bdeny

Cblock

Dreject

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'block' or 'reject' which behave differently than 'deny'.

First, allow SSH connections with allow. Then deny all other incoming connections with deny.

5fill in blank

hard

Fill all three blanks to disable password authentication and root login in SSH config.

Raspberry Pi

sudo sed -i 's/[1] yes/[2] no/' /etc/ssh/sshd_config
sudo sed -i 's/[3] yes/[2] no/' /etc/ssh/sshd_config
sudo systemctl restart sshd

Drag options to blanks, or click blank then click option'

APermitRootLogin

Bno

CPasswordAuthentication

Dyes

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up the config options or using 'yes' instead of 'no'.

Replace PasswordAuthentication yes with no to disable password login, and PermitRootLogin yes with no to disable root login.

Practice

1. What is the main benefit of using SSH keys instead of passwords to access your Raspberry Pi?

easy

A. It improves security by avoiding password guessing attacks.

B. It makes the Raspberry Pi run faster.

C. It allows multiple users to share the same password.

D. It disables the firewall automatically.

Solution

1. Step 1: Understand SSH key authentication

   SSH keys use a pair of cryptographic keys to authenticate users without sending passwords over the network.

2. Step 2: Compare with password authentication

   Password authentication can be vulnerable to guessing or brute force attacks, while SSH keys are much harder to crack.

3. Final Answer:

   It improves security by avoiding password guessing attacks. -> Option A

4. Quick Check:

   SSH keys = better security [OK]

Hint: SSH keys stop password guessing attacks fast [OK]

Common Mistakes:

• Thinking SSH keys make the device faster
• Believing SSH keys share passwords
• Assuming SSH keys disable firewall

2. Which command correctly generates an SSH key pair on your Raspberry Pi?

easy

A. ssh-keygen --firewall

B. ssh-keygen -p rsa

C. ssh-keygen -t rsa

D. firewall-cmd --generate-key

Solution

1. Step 1: Identify the SSH key generation command

   The standard command to create SSH keys is ssh-keygen with the -t option to specify the type, e.g., rsa.

2. Step 2: Check options for correctness

   -p changes the passphrase, --firewall and firewall-cmd are unrelated to SSH keys.

3. Final Answer:

   ssh-keygen -t rsa -> Option C

4. Quick Check:

   ssh-keygen -t rsa = generate SSH keys [OK]

Hint: Use ssh-keygen with -t to specify key type [OK]

Common Mistakes:

• Using -p instead of -t for key generation
• Confusing firewall commands with SSH key commands
• Trying to generate keys with firewall tools

3. Given the following commands run on a Raspberry Pi, what will be the output of sudo ufw status?

sudo ufw enable
sudo ufw allow ssh
sudo ufw deny 80

medium

A. Error: ufw command not found

B. Status: inactive

C. Status: active
No rules defined

D. Status: active
To Action From
-- ------ ----
22/tcp ALLOW Anywhere
80 DENY Anywhere

Solution

1. Step 1: Analyze the firewall commands

   sudo ufw enable activates the firewall. sudo ufw allow ssh opens port 22 (SSH). sudo ufw deny 80 blocks HTTP port 80.

2. Step 2: Understand the status output

   The status shows active firewall with rules allowing SSH (port 22) and denying port 80.

3. Final Answer:

   Status: active To Action From -- ------ ---- 22/tcp ALLOW Anywhere 80 DENY Anywhere -> Option D

4. Quick Check:

   Firewall enabled with SSH allow and port 80 deny = Status: active To Action From -- ------ ---- 22/tcp ALLOW Anywhere 80 DENY Anywhere [OK]

Hint: Enable ufw then add rules to see them in status [OK]

Common Mistakes:

• Assuming firewall is inactive after enabling
• Expecting no rules after adding allow/deny
• Confusing port numbers with service names

4. You tried to add your SSH public key to ~/.ssh/authorized_keys but still get password prompts. What is the most likely cause?

medium

A. The authorized_keys file has incorrect permissions.

B. The Raspberry Pi firewall is disabled.

C. You forgot to restart the SSH service.

D. You used the wrong SSH key type.

Solution

1. Step 1: Check SSH key authentication requirements

   SSH requires strict permissions on ~/.ssh and authorized_keys files to allow key login.

2. Step 2: Identify common permission issues

   If permissions are too open, SSH ignores the keys and falls back to password login.

3. Final Answer:

   The authorized_keys file has incorrect permissions. -> Option A

4. Quick Check:

   Wrong permissions block SSH key login [OK]

Hint: Check .ssh and authorized_keys permissions first [OK]

Common Mistakes:

• Thinking firewall affects SSH key login
• Restarting SSH service unnecessarily
• Assuming wrong key type without checking permissions

5. You want to secure your Raspberry Pi by allowing SSH access only from a specific IP address 192.168.1.100 and blocking all other SSH attempts. Which ufw commands achieve this?

hard

A. sudo ufw allow from any to any port 22
sudo ufw deny from 192.168.1.100

B. sudo ufw allow from 192.168.1.100 to any port 22
sudo ufw deny 22

C. sudo ufw deny ssh
sudo ufw allow 22

D. sudo ufw allow ssh
sudo ufw deny from 192.168.1.100 to any port 22

Solution

1. Step 1: Allow SSH only from the specific IP

   Use sudo ufw allow from 192.168.1.100 to any port 22 to permit SSH from that IP.

2. Step 2: Deny all other SSH connections

   Use sudo ufw deny 22 to block SSH from all other IPs.

3. Final Answer:

   sudo ufw allow from 192.168.1.100 to any port 22 sudo ufw deny 22 -> Option B

4. Quick Check:

   Allow specific IP then deny all others = sudo ufw allow from 192.168.1.100 to any port 22 sudo ufw deny 22 [OK]

Hint: Allow specific IP first, then deny all others [OK]

Common Mistakes:

• Allowing SSH globally before denying specific IP
• Denying the allowed IP instead of others
• Using wrong port numbers or commands