GitHub SSH Keys Authentication

What is SSH and Why Use It?

SSH (Secure Shell) is a network protocol that allows secure communication between two computers. When using SSH with GitHub, a cryptographic key pair is set up — a private key that stays on the local machine and a public key that is shared with GitHub. This allows pushing and pulling code without typing a username and password every single time.

Real-life analogy: Think of SSH keys like a padlock and a key. The public key is like a padlock — it can be given to anyone (GitHub). The private key is like the key that opens that padlock — it should never be shared with anyone. When connecting to GitHub, the private key proves identity without needing a password.

HTTPS vs SSH — Which to Use?

Step-by-Step: Setting Up SSH for GitHub

Step 1 — Check for Existing SSH Keys

Before generating a new key, check if one already exists:

ls ~/.ssh

If files like id_rsa, id_ed25519, or similar exist, an SSH key is already present. Skip to Step 3.

Step 2 — Generate a New SSH Key

The recommended key type today is Ed25519 (more secure and faster than the older RSA):

ssh-keygen -t ed25519 -C "your-email@example.com"

Replace the email with the GitHub email address. Git prompts for the following:

Enter file in which to save the key (/home/user/.ssh/id_ed25519): [Press Enter]
Enter passphrase (empty for no passphrase): [Enter a secure passphrase or press Enter for none]
Enter same passphrase again: [Repeat or press Enter]

Two files are created:

• ~/.ssh/id_ed25519 — The private key (never share this)
• ~/.ssh/id_ed25519.pub — The public key (share this with GitHub)

On systems that do not support Ed25519, use RSA with 4096 bits:

ssh-keygen -t rsa -b 4096 -C "your-email@example.com"

Step 3 — Start the SSH Agent

The SSH agent manages keys in memory so the passphrase does not need to be re-entered each session:

On Linux/macOS:

eval "$(ssh-agent -s)"
ssh-add ~/.ssh/id_ed25519

On Windows (Git Bash):

eval $(ssh-agent -s)
ssh-add ~/.ssh/id_ed25519

Step 4 — Copy the Public Key

The public key needs to be copied and added to GitHub. Display the public key:

cat ~/.ssh/id_ed25519.pub

Output example:

ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIAbCdEfGhIjKlMnOpQrStUvWxYz your-email@example.com

Copy the entire output. On Linux, a clipboard copy tool can be used:

# On Linux with xclip
xclip -selection clipboard < ~/.ssh/id_ed25519.pub

# On macOS
pbcopy < ~/.ssh/id_ed25519.pub

Step 5 — Add the Public Key to GitHub

1. Log in to github.com
2. Click the profile picture (top-right) → Settings
3. In the left sidebar, click "SSH and GPG keys"
4. Click "New SSH key"
5. Enter a descriptive title (e.g., "Home Laptop" or "Work PC")
6. Paste the public key into the "Key" field
7. Click "Add SSH key"
8. Confirm the GitHub password if prompted

Step 6 — Test the SSH Connection

ssh -T git@github.com

If the connection is successful:

Hi ravikumar! You've successfully authenticated, but GitHub does not provide shell access.

Using SSH URLs Instead of HTTPS

After SSH is set up, use SSH URLs for repositories instead of HTTPS URLs.

Clone Using SSH

git clone git@github.com:username/repository.git

Change an Existing Remote from HTTPS to SSH

# Check current remote
git remote -v
# origin  https://github.com/username/repository.git (fetch)

# Change to SSH
git remote set-url origin git@github.com:username/repository.git

# Verify
git remote -v
# origin  git@github.com:username/repository.git (fetch)

Managing Multiple SSH Keys

If different SSH keys are needed for different GitHub accounts (e.g., personal and work), a configuration file can direct which key to use:

# Create or edit ~/.ssh/config
nano ~/.ssh/config

Add the following:

# Personal GitHub account
Host github-personal
  HostName github.com
  User git
  IdentityFile ~/.ssh/id_ed25519_personal

# Work GitHub account
Host github-work
  HostName github.com
  User git
  IdentityFile ~/.ssh/id_ed25519_work

Then use the custom host alias when cloning:

git clone git@github-personal:personaluser/repo.git
git clone git@github-work:workorg/repo.git

Removing an SSH Key from GitHub

1. Go to GitHub → Settings → SSH and GPG keys
2. Find the key to remove
3. Click "Delete"

Summary

SSH keys provide a secure, passwordless way to authenticate with GitHub. The process is: generate a key pair with ssh-keygen, add the private key to the SSH agent, and upload the public key to GitHub. After setup, use SSH URLs (git@github.com:user/repo.git) for all operations. SSH is the recommended authentication method for regular Git users.