SSH Master Learning Roadmap

@amitmund June 25, 2026

SSH Mastery Roadmap

Complete Numbered Learning Path (Beginner → Expert)

Structure:

Each major topic has a unique number. Later, we will create one dedicated markdown lesson per topic.

Every lesson will contain:

Theory

Internal Working

Diagrams

Commands

Code Examples

Real-world Examples

Production Examples

Common Mistakes

Troubleshooting

Security Notes

Interview Questions

Hands-on Labs

Any Hacks

Any workaround

Exercises

Quiz

PHASE 1 — SSH FOUNDATIONS

1. What is SSH?

Learn:

History of SSH
Why SSH was created
Problems with Telnet
Secure communication concepts
SSH use cases

Example:

ssh user@server

2. SSH Architecture

Learn:

Client
Server
Session
Transport Layer
Authentication Layer
Connection Layer

Diagram:

+------------+
| SSH Client |
+------------+
       |
       | Encrypted Channel
       |
+------------+
| SSH Server |
+------------+

3. Installing SSH

Learn:

Linux

sudo apt install openssh-client
sudo apt install openssh-server

Verify

ssh -V

Service Status

sudo systemctl status ssh

4. SSH Connection Lifecycle

Understand every step:

1. DNS Resolution
2. TCP Connection
3. Version Exchange
4. Algorithm Negotiation
5. Key Exchange
6. Authentication
7. Session Creation
8. Interactive Shell

5. First SSH Connection

Example:

ssh [email protected]

Common Errors:

Permission denied

Connection refused

Connection timed out

Host key verification failed

PHASE 2 — AUTHENTICATION

6. Password Authentication

Example:

ssh user@server

Topics:

Password Login
PAM
Security Risks
Brute Force Attacks

7. Public Key Authentication

Example:

ssh-keygen

Learn:

Private Key
Public Key
Challenge Response Authentication

8. SSH Key Types

Learn:

RSA

ssh-keygen -t rsa

ED25519

ssh-keygen -t ed25519

ECDSA

ssh-keygen -t ecdsa

Comparison:

RSA
ECDSA
ED25519

9. SSH Key Generation Deep Dive

Example:

ssh-keygen -t ed25519 -C "my-key"

Learn:

Entropy
Randomness
Passphrases
Key Strength

10. authorized_keys File

Location:

~/.ssh/authorized_keys

Learn:

Format
Restrictions
Security

Example:

ssh-ed25519 AAAAC3...

11. Host Keys

Location:

/etc/ssh/ssh_host_ed25519_key

Purpose:

Server Identity Verification

12. known_hosts File

Location:

~/.ssh/known_hosts

Purpose:

Store trusted server fingerprints

13. SSH Fingerprints

Example:

ssh-keygen -lf key.pub

Learn:

SHA256 Fingerprints
Verification Process

PHASE 3 — CONFIGURATION

14. SSH Client Configuration

File:

~/.ssh/config

Example:

Host prod
    HostName 10.0.0.5
    User ubuntu
    Port 2222

15. SSH Server Configuration

File:

/etc/ssh/sshd_config

Example:

PermitRootLogin no
PasswordAuthentication no
PubkeyAuthentication yes

16. SSH Ports

Default:

Custom:

2222
2200
22222

Examples:

AllowUsers
AllowGroups
DenyUsers
DenyGroups

Example:

Authorized Users Only

Learn:

Legal Banners
Compliance Requirements

PHASE 4 — SECURITY

19. SSH Hardening

Learn:

Disable Root Login
Disable Password Authentication
Restrict Users
Strong Ciphers

20. SSH Security Best Practices

Checklist:

✓ Key Authentication
✓ Fail2Ban
✓ MFA
✓ Least Privilege
✓ Auditing

21. SSH Cipher Suites

Examples:

AES128
AES256
ChaCha20

22. MAC Algorithms

Examples:

hmac-sha2-256
hmac-sha2-512

23. Key Exchange Algorithms

Examples:

Diffie-Hellman
ECDH
Curve25519

24. SSH Security Auditing

Tools:

ssh-audit

25. Fail2Ban with SSH

Example:

sudo apt install fail2ban

Purpose:

Block Brute Force Attacks

PHASE 5 — FILE TRANSFER

26. SCP

Upload:

scp file.txt user@server:/tmp

Download:

scp user@server:/tmp/file.txt .

27. SFTP

Connect:

sftp user@server

Commands:

put
get
ls
cd

28. Rsync over SSH

Example:

rsync -avz -e ssh src/ user@server:/backup

PHASE 6 — SSH AGENTS

29. SSH Agent

Start:

eval "$(ssh-agent -s)"

Add Key:

ssh-add ~/.ssh/id_ed25519

30. SSH Agent Forwarding

Example:

ssh -A user@server

PHASE 7 — ADVANCED CONNECTIONS

31. Jump Hosts (Bastion Hosts)

Diagram:

Laptop
   |
Bastion
   |
Private Server

32. ProxyJump

Example:

ssh -J bastion internal-server

33. ProxyCommand

Example:

ProxyCommand ssh bastion nc %h %p

34. SSH Multiplexing

Example:

ControlMaster auto
ControlPersist 10m

PHASE 8 — TUNNELING

35. Local Port Forwarding

Example:

ssh -L 8080:localhost:80 user@server

Diagram:

Browser
   |
localhost:8080
   |
SSH Tunnel
   |
Server:80

36. Remote Port Forwarding

Example:

ssh -R 8080:localhost:3000 user@server

37. Dynamic Port Forwarding

Example:

ssh -D 1080 user@server

Purpose:

SOCKS Proxy

38. Reverse SSH Tunnels

Learn:

NAT Traversal
Remote Access

PHASE 9 — PROTOCOL INTERNALS

39. SSH Handshake

Learn:

Version Exchange
Algorithm Negotiation
Key Exchange
Authentication

40. Transport Layer Protocol

Learn:

Encryption
Compression
Integrity

41. Authentication Layer Protocol

Learn:

Password
Public Key
Keyboard Interactive

42. Connection Layer Protocol

Learn:

Channels
Sessions
Port Forwarding

43. Packet Structure

Learn:

Packet Header
Payload
MAC
Padding

44. Cryptography Behind SSH

Learn:

AES
RSA
ECDSA
ED25519
Curve25519
SHA256

PHASE 10 — TROUBLESHOOTING

45. SSH Debugging

Example:

ssh -v user@server

More Detail:

ssh -vv

Maximum:

ssh -vvv

46. SSH Logs

Ubuntu:

/var/log/auth.log

RHEL:

/var/log/secure

47. Common SSH Errors

Examples:

Permission denied

Connection refused

Broken pipe

Host key verification failed

No route to host

PHASE 11 — PRODUCTION SSH

48. SSH in AWS

Learn:

EC2 Key Pairs
Security Groups

49. SSH in Azure

Learn:

Azure VM SSH Access

50. SSH in Google Cloud

Learn:

OS Login
Metadata Keys

51. SSH Automation

Examples:

ssh server "uptime"

ssh server "systemctl restart nginx"

52. SSH with Ansible

Example:

ansible all -m ping

53. Git over SSH

Example:

git clone [email protected]:user/repo.git

PHASE 12 — ENTERPRISE & EXPERT LEVEL

54. SSH Certificates

Learn:

Certificate Authority
Signed Keys
Trust Model

55. OpenSSH Internals

Learn:

sshd
ssh
ssh-agent
sftp-server

56. OpenSSH Source Code Walkthrough

Study:

Authentication Flow
Connection Handling
Packet Processing

57. SSH Honeypots

Tool:

Cowrie

58. SSH Packet Analysis

Tools:

tcpdump

wireshark

59. SSH Compliance & Auditing

Learn:

CIS Benchmarks
NIST
PCI-DSS
ISO 27001

60. Building an Enterprise SSH Architecture

Topics:

Bastion Hosts
Certificates
MFA
Centralized Access
Auditing
Logging
Monitoring

FINAL CAPSTONE PROJECTS

Project 1

Build Secure Home Lab SSH Infrastructure

Project 2

Deploy SSH-Based Linux Administration Environment

Project 3

Create Bastion Host Architecture

Project 4

Build SSH Certificate Authority

Project 5

Perform Full SSH Security Audit

Project 6

Analyze SSH Packets Using Wireshark

Learning Order

01 → 05 Fundamentals

06 → 13 Authentication

14 → 18 Configuration

19 → 25 Security

26 → 28 File Transfer

29 → 30 SSH Agent

31 → 34 Advanced Connections

35 → 38 Tunneling

39 → 44 Protocol Internals

45 → 47 Troubleshooting

48 → 53 Production Usage

54 → 60 Enterprise / Expert

Next Lesson

Topic #1

"What is SSH?"

We will cover it in extreme depth: - History - Why SSH Exists - How SSH Works - Internal Architecture - Encryption Basics - Authentication Basics - Packet Flow - Real World Examples - Labs - Exercises - Quiz - Interview Questions

SSH Mastery Roadmap

Complete Numbered Learning Path (Beginner → Expert)

PHASE 1 — SSH FOUNDATIONS

1. What is SSH?

2. SSH Architecture

3. Installing SSH

Linux

Verify

Service Status

4. SSH Connection Lifecycle

5. First SSH Connection

PHASE 2 — AUTHENTICATION

6. Password Authentication

7. Public Key Authentication

8. SSH Key Types

RSA

ED25519

ECDSA

9. SSH Key Generation Deep Dive

10. authorized_keys File

11. Host Keys

12. known_hosts File

13. SSH Fingerprints

PHASE 3 — CONFIGURATION

14. SSH Client Configuration

15. SSH Server Configuration

16. SSH Ports

17. SSH Login Restrictions

18. SSH Banner Configuration

PHASE 4 — SECURITY

19. SSH Hardening

20. SSH Security Best Practices

21. SSH Cipher Suites

22. MAC Algorithms

23. Key Exchange Algorithms

24. SSH Security Auditing

25. Fail2Ban with SSH

PHASE 5 — FILE TRANSFER

26. SCP

27. SFTP

28. Rsync over SSH

PHASE 6 — SSH AGENTS

29. SSH Agent

30. SSH Agent Forwarding

PHASE 7 — ADVANCED CONNECTIONS

31. Jump Hosts (Bastion Hosts)

32. ProxyJump

33. ProxyCommand

34. SSH Multiplexing

PHASE 8 — TUNNELING

35. Local Port Forwarding

36. Remote Port Forwarding

37. Dynamic Port Forwarding

38. Reverse SSH Tunnels

PHASE 9 — PROTOCOL INTERNALS

39. SSH Handshake

40. Transport Layer Protocol

41. Authentication Layer Protocol

42. Connection Layer Protocol

43. Packet Structure

44. Cryptography Behind SSH

PHASE 10 — TROUBLESHOOTING

45. SSH Debugging

46. SSH Logs

47. Common SSH Errors

PHASE 11 — PRODUCTION SSH

48. SSH in AWS

49. SSH in Azure

50. SSH in Google Cloud

51. SSH Automation

52. SSH with Ansible

53. Git over SSH

PHASE 12 — ENTERPRISE & EXPERT LEVEL

54. SSH Certificates

55. OpenSSH Internals

56. OpenSSH Source Code Walkthrough

57. SSH Honeypots

58. SSH Packet Analysis

59. SSH Compliance & Auditing

60. Building an Enterprise SSH Architecture