<![CDATA[Keys and More]]>https://pairoshousekeys.hashnode.devRSS for NodeFri, 11 Sep 2026 11:00:08 GMT60<![CDATA[๐Ÿ” SSH & Key Pairs Explained End-to-End (AWS EC2 | From Basics to Advanced)]]>https://pairoshousekeys.hashnode.dev/ssh-and-key-pairs-explained-end-to-end-aws-ec2-from-basics-to-advancedhttps://pairoshousekeys.hashnode.dev/ssh-and-key-pairs-explained-end-to-end-aws-ec2-from-basics-to-advancedTue, 06 Jan 2026 18:17:14 GMTSSH key pairs are backbone for cloud, linux and DevOps security practices. In this article, we will understand what SSH is and how it works and how an EC2 instance can be accessible even without a key pair.

What is SSH?

First things first, what is S.S.H?

ssh (Secure shell) is a secure protocol used to connect to remote Linux servrs.

  • Encrypts communication

  • Replaces insecure password login

  • Industry standard for server access.

In Simple words:

| SSH lets you safely login into another computer over the network.

๐Ÿ” What is an SSH Key Pair?

An SSH Key pair has two keys:

Key Purpose Share

Private Key Proves identity โŒ

Public Key Verifies identity โœ…

The default location of SSH files is ~/.ssh

some of the important files you can find

  1. id_ed25519 โ†’ private key

  2. id_ed25519.pub โ†’ public key

  3. authorized_keys โ†’ allowed public keys on server

To generate the SSH Key pair of your machine

ssh-keygen -t ed25519

๐Ÿข How SSH Authentication Works

participant Client participant Server

Client->>Server: SSH request

Server->>Client: Challenge

Client->>Server: Signed using private key

Server->>Server: Verify using public key

Server-->>Client: Access granted

โš ๏ธ Private key should neven leave your machine.

SSH in AWS EC2 (Normal Flow)

When launching EC2:

โ€”> AWS asks for key pair

โ€”> Public key is stored in:

~/.ssh/authroized_keys

Connect to SSH Using:

ssh -i key.pem ubuntu@ยซec2-IPยป

Different scenarios to connect

Scenarion 1: Connect EC2(A) โ€”> EC2 (B) [No Password]

on EC2-A

ssh-keygen -t ed25519 (take the public key on ec2(A))

cat ~/.ssh/id_ed25519.pub

on EC2-B

paste the public key of ec2(A) and keep it in Authorised keys of B

~/.ssh/authorized_keys

Now login to EC2(B) using EC2(A)

Quick and Faster method โšก

ssh-copy-id ubuntu@ยซEC2-IPยป

This above command will handle on permissions and keys.

Scenario 2: EC2 Launched Without Key Pair ๐Ÿ˜จ

First Method: Reuse Another instance key

โ€”> Copy the public key from EC2-A

โ€”> Add to EC2-B authorized_keys

โ€”> Login using EC2-A Private key

Second Method: AWS SSM (Most used)

Enable SSM Agent

Attach IAM role

Login without SSH or keys

๐Ÿ” Production Best Practices

  • Disable password login

  • Use key-based auth only

  • Restrict SSH IPs

  • Rotate keys

  • Prefer AWS SSM

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