SSH protocol fully explained.

Aditya Raj

2 min read

·

Apr 22, 2026

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Today I took a deep dive into SSH (Secure Shell) — one of the most fundamental tools in backend development and DevOps.

At its core, SSH is a cryptographic network protocol that allows secure communication between two systems over a network. It’s most commonly used for:

• Logging into remote machines
• Executing commands on servers
• Secure file transfer

Why SSH is Important

When working with remote servers (like cloud VMs or deploying applications), security is critical.

SSH ensures:

1. Encryption
All data exchanged between client and server is encrypted, so even if someone intercepts it, they can’t read it.

2. Authentication
SSH verifies identity using:

• Password-based login (less secure)
• Public key authentication (recommended)

3. Integrity
It ensures that data is not modified during transmission.

SSH Key-Based Authentication

SSH uses asymmetric encryption, which involves two keys:

• Private Key → stays on your machine (never share)
• Public Key → shared with servers like GitHub or Amazon Web Services

How Authentication Works ?

Simple Flow —

1. Client sends a connection request
2. Server sends a random challenge
3. Client signs the challenge using its private key
4. Server verifies it using the stored public key
5. If valid → access granted (no password needed)

This is exactly what makes SSH both secure and seamless.

SSH Key Algorithms

Common algorithms used for generating SSH keys:

• RSA (older, widely supported)
• ED25519 (modern, fast, recommended)
• ECDSA

Working with SSH Keys

To generate a key:

ssh-keygen -t ed25519

For multiple keys (best practice):

ssh-keygen -t ed25519 -f ~/.ssh/github_key
ssh-keygen -t ed25519 -f ~/.ssh/aws_key

Why Multiple SSH Keys?

Instead of using one key everywhere, it’s better to create separate keys for:

• GitHub
• Cloud servers (AWS, VPS)
• Personal projects

This provides:

• Better security
• Easy access control
• Safer key rotation

** Important Concept I Learned **

While creating keys, the file path matters:

• ~/.ssh/key_name → correct location
• key_name → saved in current directory
• ~/.ssh/id_ed25519/new_key → invalid (because id_ed25519 is a file, not a folder)

Final Understanding

SSH is not just a tool — it’s a secure identity system for machines.

• It replaces passwords
• It powers deployments
• It’s heavily used in DevOps workflows

> SSH keys are your digital identity for secure communication, and using multiple keys is the foundation of a professional DevOps setup.

Still exploring deeper into SSH and DevOps.

Next step: connecting this knowledge to real deployments