SSH

Secure Shell Protocol

SSH is a cryptographic network protocol for operating network services securely over an unsecured network. OpenSSH is a suite of secure networking utilities based on the Secure Shell Protocol.

Usage

ssh - Connect to a remote server.

ssh user@ip_address

• Use the -i flag to specify the identity file.

ssh-add - Add keys to the ssh-agent.

• -l - Lists fingerprints of all identities currently represented by the agent.
• -d - Removes identities from the agent.

ssh-keygen - Generate new keys. ssh-copy-id - Copy keys to remote servers. It will prompt you for the password.

ssh-copy-id -i ~/.ssh/id_rsa.pub user@ip_address

Configuration

Files

• ~/.ssh/config - Main configuration file.
• ~/.ssh/known_hosts - Stores the fingerprints of the servers we have connected to. Useful for preventing the man-in-the-middle attack.
• ~/.ssh/authorized_keys - Stores the public keys of the identities that can connect to the server.

chmod these file with 600 permission.

Examples

Host configuration. This allows you to run ssh myserver instead of ssh user@ip_address. We can also specify the ssh key we want to use.

Host myserver
  Hostname ip_address
  Port 22
  User user
  IdentityFile ~/.ssh/id_ed25519

Add keys to the agent after the first use.

AddKeysToAgent yes

Resources

• OpenSSH Full Guide - Everything you need to get started! #media/video
• How Secure Shell Works (SSH) - Computerphile #media/video
• SSH Kung Fu #media/article