📘 04-04: Secure Protocols & Encryption¶
💡 Why Encryption?¶
Plaintext protocols (Telnet, HTTP, FTP) expose credentials and data to sniffers. Secure protocols add confidentiality, integrity, and authentication.
📌 TLS / SSL¶
- TLS (Transport Layer Security) — successor to SSL — encrypts sessions and authenticates servers via certificates.
- Secures HTTPS (443), secure email (993/995/587), and more.
- Operates around the Session/Presentation layers.
📌 SSH¶
- SSH (Secure Shell, port 22) provides encrypted remote CLI access, key-based auth, and secure tunneling.
- Basis for SFTP and SCP (secure file transfer).
- Replaces insecure Telnet (23).
📌 IPsec¶
- IPsec secures traffic at Layer 3 (Network), encrypting/authenticating IP packets.
- Two core protocols:
- AH (Authentication Header) — integrity/authentication
- ESP (Encapsulating Security Payload) — encryption (+ optional integrity)
- IKE negotiates keys. Widely used to build VPNs.
📌 Secure vs. Insecure Reference¶
| Insecure | Secure |
|---|---|
| Telnet (23) | SSH (22) |
| HTTP (80) | HTTPS (443) |
| FTP (20/21) | SFTP (22) / FTPS |
| SNMPv1/2c | SNMPv3 |
| POP3/IMAP (110/143) | POP3S/IMAPS (995/993) |
Tip
Key idea — Prefer secure protocols: TLS for web/app data, SSH for remote CLI, IPsec for VPN tunnels at Layer 3. Always replace Telnet/HTTP/FTP with encrypted equivalents.
See also: Remote Access, Firewalls & ACLs
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