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How to Generate SSH Keys on a Mac: An In-Depth Walkthrough

Overview

This comprehensive guide will teach you how to generate secure SSH key pairs on your Mac. We cover everything from understanding different SSH key algorithms to practical steps for creating keys using the built-in macOS Terminal app.

You‘ll also learn expert-recommended best practices for deploying keys, enhancing security, troubleshooting connections, and managing keys as an experienced SSH user.

Follow along to master SSH key-based authentication on your Mac.

What is SSH? A Brief History

SSH stands for "Secure Shell". It‘s a cryptographic network protocol originating in 1995 that allows establishing a secure channel between two network devices – typically a client and a server.

According to SSH.com, SSH was invented as a more secure replacement for remote access protocols like Telnet and rlogin that sent data including passwords in plain text. Early versions of SSH focused only on user authentication without data encryption.

Over time, SSH implemented various encryption algorithms for data privacy including symmetric ciphers like AES and asymmetric encryption through public-key cryptography. This evolution paved the way for wide adoption of SSH for administering remote systems and devices.

Now SSH is a universal standard included on virtually all operating systems. Both client and server components are readily available. Today, SSH is most commonly used for:

  • Securely logging onto remote systems for command execution, administration etc.
  • Copying files to/from remote hosts through SFTP and SCP protocols.
  • Tunneling – creating an encrypted SSH tunnel for sending traffic securely.
  • Automating remote tasks by executing commands/scripts via SSH programmatically.

Next, we‘ll understand more about how SSH key-based user authentication works…

How SSH Key Authentication Works

SSH utilizes public-key cryptography to verify user identities in a highly secure manner before granting access. This is preferred over password-based authentication that can be guessed or cracked.

Here‘s an overview:

  • Each user generates a key pair consisting of a private key and a public key using the ssh-keygen command.
  • The private key stays exclusively on the client machine. It serves as the digital identity credential for authentication.
  • The public key gets stored on any remote server that needs to allow access for the user.
  • When the user tries SSH‘ing into a server, the private key encrypts a challenge message from the server. This is sent to the server.
  • The server then uses the stored public key to decrypt the message. If decryption succeeds, the user‘s identity is verified since only the private key could have encrypted that message.
  • An encrypted session gets established with the user granted access to the server. No passwords get transmitted.

This handshake demonstrates to the SSH server that the client possesses the corresponding private key without revealing what that key is. Public-key encryption enables establishing the encrypted SSH session used for conducting remote administration securely.

Now let‘s see this handshake in action by generating keys on your Mac…

Generating SSH Keys on Mac

Here is a step-by-step walkthrough for creating SSH key pairs on Mac:

Launch Terminal App

The Terminal app provides command-line interface access on Mac. It‘s located in Applications -> Utilities or can be quickly launched with the keyboard shortcut command + spacebar, then typing Terminal.

Launch Terminal to get started.

Run the ssh-keygen Command

At the Terminal prompt, enter the following command then hit return:

ssh-keygen

This launches the SSH key generation process for RSA and DSA key types by default.

Running ssh-keygen command

Select Key Type and Key Length

First, you need to confirm the type of key you want to create. RSA keys are the most common.

Generating public/private rsa key pair.

Press enter to accept the default RSA keys.

Next, select a key length. Larger key lengths enhance security but have a slight performance impact.

Enter file in which to save the key (/Users/demouser/.ssh/id_rsa): /Users/demouser/.ssh/id_rsa
Enter passphrase (empty for no passphrase):

The default 2048-bit key length provides robust security for most purposes. Press enter to accept.

Add an Optional Passphrase

Now you will be prompted to add an optional passphrase which functions as a password.

Adding a passphrase provides an extra layer of security to prevent unauthorized usage of the keys. However, it does require entering the passphrase each time you use the key for authentication.

Press enter to skip adding a passphrase. Or enter a complex one if desired. Confirm it by entering it again.

Save Public and Private Keys

After confirming details, your SSH key pair is generated containing:

  • Private key: /Users/demouser/.ssh/id_rsa
  • Public key: /Users/demouser/.ssh/id_rsa.pub

The private and public key files get stored in your .ssh directory.

Private keys should remain only on your local machine and no where else. This protects your identity credential from getting compromised.

Public keys need copied over and installed onto any remote servers you wish to access using key-based SSH authentication.

And that‘s it! You‘ve successfully created an SSH key pair on your Mac.

Now let‘s look at some recommended best practices for using SSH keys effectively.

SSH Keys Best Practices

Here are some expert tips for enhancing security and avoiding pitfalls when working with SSH keys:

Use SSH Agent to Manage Keys

The SSH agent handles decrypting your private keys. Rather than manually loading keys each time, add them to ssh-agent instead.

Edit the config file at ~/.ssh/config:

Host *
  AddKeysToAgent yes
  UseKeychain yes
  IdentityFile ~/.ssh/id_rsa

Then run:

$ ssh-add -K ~/.ssh/id_rsa

This adds your key to both ssh-agent and MacOS keychain for ease of use.

Protect Private Keys

  • Store private keys only on trusted local devices you directly control, with permissions set to read-only for your user account only.
  • Consider encrypting the .ssh directory containing private keys for extra safety.
  • Backup your private keys to external media in case devices are lost or damaged. But handle backups securely as well.

Following this principle of least privilege for key access is vital.

Revoke Keys if Compromised

If you suspect a private key has been stolen, compromise or lost, immediately regenerate a new key pair. Then replace the old public keys on any servers with your newly generated public key.

Also review server logs and user accounts to ensure no unauthorized access occurred through the old keys. Prompt key rotation limits the window for attacks.

Use Strong Passphrases

Passphrases should be 20+ characters, containing upper and lower case letters, numbers and symbols to make them harder to crack.

A long passphrase provides substantial security. But consider balancing convenience against risks based on your use case.

These tips will help avoid many pitfalls that lead to compromised keys causing security headaches.

Troubleshooting SSH Issues

Here are some common troubleshooting tips for debugging SSH connections:

Permission denied errors – Ensure correct file permissions are set for the .ssh directory (700) and private key files (600) on client. Also confirm correct ownership by the user account.

Protocols mismatch – Happens when server and client don‘t have common preferred SSH protocols in common. Edit /etc/ssh/sshd_config and ~/.ssh/config files to add desired protocol like Protocol 2.

DNS resolution failures – Try connecting using server IP address instead of hostname. Also confirm DNS name services can resolve hostnames correctly.

Incorrect login credentials – Double check the username being passed to SSH ssh demouser@server, and how that username is defined on target system.

Firewall blocking traffic – Confirm necessary port is open (default port 22) and SSH traffic is allowed both locally and remotely.

Checking these common items often reveals what‘s breaking down with getting SSH connections fully established.

SSH Clients for Mac

The built-in Terminal on Mac provides basic SSH functionality via the ssh command. But many third party clients available for MacOS offer additional conveniences:

  • Termius – Free SSH client with native M1 support, multi-session tabs, platform syncing and works with LDAP.

  • Microsoft Remote Desktop – Feature packed remote desktop client with SSH tunneling capabilities built-in.

  • Secure ShellFish – Open source client focusing on ease of use, with custom commands and proxy jump support.

These Mac SSH clients provide features like tabbed sessions, bookmarking hosts, agent forwarding configuration, dynamic port forwarding (SOCKS proxy), and syncing your sessions/settings across devices.

Termius SSH client example

Many also integrate directly with ssh-agent rather than having to run the ssh-add command manually. Convenience features that enhance workflows for tech professionals relying on SSH everyday.

Going Further with SSH Keys

We‘ve covered the basics of generating keys as well as best practices and troubleshooting. Here are some additional topics for taking your SSH skills to the next level:

  • Understand SSH protocols – From early protocl 1 to the secure current version 2, knowing protocol handshakes assists debugging.
  • Utilize config files – The system-wide sshd_config and user ~/.ssh/config files allow customizing connections.
  • Configure SSH tunnels – Forward remote ports through an intermediary SSH jump server for access control.
  • Automate SSH commands – Script routine SSH logins, commands and file transfers for efficiency.
  • Implement SSH certificates – Signed keys issued by internal certificate authorities, managed through an SSH CA.
  • Integrate with LDAP/Kerberos – Centralized authentication control mechanisms compatible with SSH user keys.

This foundational guide has equipped you to actively utilize SSH key pairs on MacOS for enhanced security. Now build on this knowledge to become a SSH power user!

Conclusion

You should now have a solid grasp of generating SSH key pairs on your Mac using the ssh-keygen command in Terminal app.

We discussed what SSH is, how key-based authentication establishes secure connections as well as steps for creating RSA keys and best practices for managing them.

You also have troubleshooting guidance for diagnosing SSH issues should they arise. And a primer on third party SSH clients offering additional features.

From here you can confidently put your skills to use for administering remote systems with the assurance of SSH security protecting access.

Our guide was intended to provide extensive, authoritative information on SSH keys targeted for a MacOS audience looking to deeply understand this technology. Please let me know if you have any other questions!

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