SSH (Secure Shell)
Secure remote access protocol with key-based authentication and encrypted communications
What is SSH?
SSH (Secure Shell) is a cryptographic network protocol that provides secure remote access to systems over an unsecured network. It replaces insecure protocols like Telnet and rlogin.
Key Features:
- Encryption: All communication encrypted
- Authentication: Multiple auth methods
- Integrity: Data tampering detection
- Port Forwarding: Tunnel other protocols
- File Transfer: SCP and SFTP support
- X11 Forwarding: Remote GUI applications
- Agent Forwarding: Key management
- Compression: Bandwidth optimization
SSH Connection Process:
1
TCP Connection
Client connects to server on port 22
→
2
Protocol Negotiation
Agree on SSH version and algorithms
→
3
Key Exchange
Establish encrypted session keys
→
4
Authentication
Verify user identity (keys/password)
→
5
Secure Session
Encrypted command execution
SSH vs Legacy Protocols
| Protocol | Port | Encryption | Authentication | Status |
|---|---|---|---|---|
| SSH | 22 | Strong | Keys, Password, MFA | Recommended |
| Telnet | 23 | None | Password (plaintext) | Deprecated |
| rlogin | 513 | None | Host-based | Deprecated |
| FTP | 21 | None | Password (plaintext) | Use SFTP |
🔐 SSH Quick Facts
- Created: 1995 by Tatu Ylönen
- Current Version: SSH-2 (RFC 4251-4254)
- Default Port: 22/tcp
- Key Algorithms: RSA, ECDSA, Ed25519
- Encryption: AES, ChaCha20-Poly1305
Common Use Cases
Remote Administration
Secure server management and configuration
Development & Deployment
Git operations, CI/CD, and code deployment
File Transfer
Secure file transfer with SCP and SFTP
Tunneling & Proxying
Port forwarding and SOCKS proxies