SSH and FTP

[!NOTE] This module explores the core principles of SSH and FTP, deriving solutions from first principles and hardware constraints to build world-class, production-ready expertise.

1. SSH (Secure Shell)

SSH is a cryptographic network protocol for operating network services securely over an unsecured network. It is the standard for remote management of Linux servers.

  • Port: 22.
  • Key Features:
  • Encryption: All traffic between client and server is encrypted.
  • Authentication: Password or Public-key based.
  • Tunneling: Can wrap other protocols (like database traffic) and send them through a secure “tunnel.”

2. FTP (File Transfer Protocol)

FTP is a legacy protocol used to move files between a client and a server.

  • Port: 21 (Command), 20 (Data).
  • The Flaw: It is completely Unencrypted. Your username and password are sent in plaintext over the wire.

The Alternatives

  1. SFTP (SSH File Transfer Protocol): FTP-like functionality running entirely inside an SSH session. (Secure).
  2. SCP (Secure Copy): Simple CLI tool to copy files over SSH. (Secure).

3. Interactive: SSH Key Exchange

See how the server is verified.

💻
Client
↔
Remote Server
SHA256: 4f1a...
Waiting for command...

4. Active vs. Passive FTP

FTP is famous for being a “Firewall Killer” because it uses two separate connections.

  • Active Mode: The server tries to connect to the client for data transfer. Most firewalls block this.
  • Passive Mode: The client connects to the server for both command and data. This is what modern clients use to get through firewalls.