Securing Raspberry Pi (SSH keys, firewall) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main benefit of using SSH keys instead of passwords for Raspberry Pi access?

SSH keys provide stronger security by using cryptographic keys instead of passwords, making it much harder for attackers to guess or brute-force access.

beginner

How do you generate an SSH key pair on your local computer?

Use the command ssh-keygen in the terminal. This creates a private key (keep secret) and a public key (share with Raspberry Pi).

beginner

What is the purpose of a firewall on a Raspberry Pi?

A firewall controls which network connections are allowed or blocked, protecting the Raspberry Pi from unwanted access or attacks.

intermediate

Which command can you use to enable the firewall on Raspberry Pi running Linux?

You can use sudo ufw enable to turn on the uncomplicated firewall (UFW) on Raspberry Pi.

intermediate

How do you add your public SSH key to the Raspberry Pi to allow key-based login?

Copy your public key to the Raspberry Pi's ~/.ssh/authorized_keys file, for example using ssh-copy-id user@raspberrypi.

What file on the Raspberry Pi stores the list of allowed SSH public keys?

A /etc/ssh/ssh_config

B ~/.ssh/authorized_keys

C ~/.ssh/id_rsa

D /etc/passwd

The file ~/.ssh/authorized_keys contains the public keys allowed for SSH login.

Which command disables password login for SSH on Raspberry Pi?

A ssh-keygen -p

B sudo ufw disable

C sudo systemctl stop ssh

D Edit /etc/ssh/sshd_config and set PasswordAuthentication no

Disabling password login requires editing /etc/ssh/sshd_config and setting PasswordAuthentication no.

What does the command sudo ufw allow 22 do?

A Disables the firewall

B Blocks SSH connections

C Allows SSH connections through the firewall

D Enables the firewall

Port 22 is the default SSH port; this command allows SSH traffic through the firewall.

Why is it important to keep your private SSH key secure?

A Because anyone with it can access your Raspberry Pi

B Because it contains your password

C Because it is stored on the Raspberry Pi

D Because it expires quickly

The private key grants access; if stolen, attackers can log in without a password.

Which tool is commonly used as a simple firewall on Raspberry Pi?

A UFW (Uncomplicated Firewall)

B iptables

C fail2ban

D Wireshark

UFW is a user-friendly firewall tool often used on Raspberry Pi.

Explain how to set up SSH key authentication on a Raspberry Pi.

Think about creating keys, sharing the public one, and securing the server.

Describe the role of a firewall on a Raspberry Pi and how to enable it.

Consider how a firewall protects and how to control access.

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