SSH (Secure Shell) is a cryptographic network protocol used for secure communication between a client and a server. Unlike Telnet, SSH encrypts all traffic including credentials making it suitable for remote administration, secure file transfers, and tunneling services.

Layer: Application (OSI Layer 7)

Port: TCP/22

Encryption: Yes (various ciphers and key exchange algorithms)

Why SSH?

SSH was designed to overcome the limitations of insecure protocols like Telnet:

• Confidentiality: Prevents eavesdropping with encryption.
• Integrity: Ensures data is not modified in transit.
• Authentication: Validates both the server and the client.
• Encryption: All communication is end-to-end encrypted.

SSH Use Cases

• Remote administration of servers
• Secure file transfer (via SCP/SFTP)
• Tunneling insecure protocols (e.g., SMTP, HTTP)
• Git repository access
• Secure automation over CI/CD pipelines

SSH Authentication Methods

SSH supports multiple authentication mechanisms: