SSH (Secure Shell) is a cryptographic network protocol for secure remote access, command execution, and data transfer over untrusted networks. It provides encrypted communication channels using public-key cryptography, replacing legacy protocols like Telnet and FTP. SSH operates on port 22 by default and is fundamental to modern system administration, DevOps workflows, and secure remote management. The key concept to remember: SSH tunnels all traffic through encrypted channels, meaning not just authentication but also all subsequent data transfer is protected—making it essential for accessing servers, managing infrastructure, and transferring files across networks without exposing sensitive information.
What This Cheat Sheet Covers
This topic spans 20 focused tables and 155 indexed concepts. Below is a complete table-by-table outline of this topic, spanning foundational concepts through advanced details.
Table 1: SSH Key Types
| Type | Example | Description |
|---|---|---|
ssh-keygen -t ed25519 -C "user@email.com" | • Most recommended modern algorithm • 256-bit Edwards-curve signature providing best performance and security with smallest key size • faster than RSA/ECDSA. | |
ssh-keygen -t rsa -b 4096 -C "user@email.com" | • Most widely supported algorithm • requires 4096-bit minimum for adequate security • slower than Ed25519 but compatible with older systems. | |
ssh-keygen -t ecdsa -b 521 -C "user@email.com" | • Elliptic curve algorithm • shorter keys than RSA • NIST curves have security concerns • less common than Ed25519 for modern deployments. |