How to Create an SSH Key

Quick idea

You’ll generate an SSH keypair, upload the public key to the service you use (GitHub/Bitbucket/etc.), and optionally configure SSH so you can use multiple keys cleanly.

Recommended key type: Ed25519.

1) Create an SSH key

ssh-keygen -t ed25519 -C "your_email@example.com"

By default, this creates:

• ~/.ssh/id_ed25519 (private key)
• ~/.ssh/id_ed25519.pub (public key)

Tip: If you want a custom filename (useful when you’ll have multiple keys):

ssh-keygen -t ed25519 -C "your_email@example.com" -f ~/.ssh/id_ed25519_custom

2) Add your key to ssh-agent (so you don’t type the passphrase every time)

Start the agent:

eval "$(ssh-agent -s)"

Add your key:

ssh-add ~/.ssh/id_ed25519

If you used a custom filename, add that instead:

ssh-add ~/.ssh/id_ed25519_custom

3) Copy your public key and add it to GitHub / Bitbucket / others

Print your public key:

cat ~/.ssh/id_ed25519.pub

If you used a custom filename:

cat ~/.ssh/id_ed25519_custom.pub

Then paste it into your provider’s SSH key settings.

4) Test your SSH connection

GitHub:

ssh -T git@github.com

Bitbucket:

ssh -T git@bitbucket.org

Note: You can use multiple SSH keys (GitHub + Bitbucket, or multiple accounts)

If you need multiple keys, generate them with different filenames, then configure ~/.ssh/config to pick the right key per host.

Example: ~/.ssh/config:

Host github.com
  HostName github.com
  User git
  IdentityFile ~/.ssh/id_ed25519_github
  IdentitiesOnly yes

Host bitbucket.org
  HostName bitbucket.org
  User git
  IdentityFile ~/.ssh/id_ed25519_bitbucket
  IdentitiesOnly yes

“Create a key with a specific public key” (what’s actually possible) You cannot generate a new private key that matches an arbitrary public key. A public key only works if you also have the matching private key.

Use an existing keypair (import your private key)

1. Put the private key file in ~/.ssh/
2. Fix permissions:

chmod 600 ~/.ssh/id_ed25519_custom

3. Re-generate the public key from the private key:

ssh-keygen -y -f ~/.ssh/id_ed25519_custom > ~/.ssh/id_ed25519_custom.pub

4. Upload that .pub to GitHub/Bitbucket.