Computer Network Notes: HTTP, HTTPS, SSH, and SSL

🌐 HTTP (HyperText Transfer Protocol)

Definition: HTTP is an application layer protocol used for transmitting hypermedia documents (like HTML) between a client (browser) and a server. It is the foundation of data communication on the World Wide Web.
Key Points:

• Operates over TCP (port 80)
• It is stateless — each request is independent
• Uses methods like GET, POST, PUT, DELETE, etc.
• Data is not encrypted, making it vulnerable to interception
• Example: http://www.example.com
  Advantages: Simple and fast for transferring data; widely supported across browsers and servers.
  Disadvantages: No encryption → vulnerable to attacks like sniffing and MITM.

🔒 HTTPS (HyperText Transfer Protocol Secure)

Definition: HTTPS is the secure version of HTTP. It uses SSL/TLS encryption to protect data transmitted between client and server.
Key Points:

• Operates over TCP (port 443)
• Provides confidentiality, integrity, and authentication
• Encrypts data before transmission, preventing eavesdropping
• Uses digital certificates from trusted Certificate Authorities (CAs)
• Example: https://www.example.com
  Advantages: Secure communication channel; builds user trust; protects sensitive data (passwords, payment info).
  Disadvantages: Slightly higher processing overhead; requires certificate management.

🧩 SSH (Secure Shell)

Definition: SSH is a cryptographic network protocol used to securely log into remote systems and execute commands over an unsecured network.
Key Points:

• Operates over TCP (port 22)
• Provides secure remote access and file transfer (via SCP or SFTP)
• Uses public-key cryptography for authentication
• Replaces insecure protocols like Telnet and rlogin
• Command Example: ssh user@hostname
  Advantages: Strong encryption; secure command execution and file transfers; supports tunneling and port forwarding.
  Disadvantages: Can be complex to configure; misconfigured keys can cause vulnerabilities.

🔐 SSL (Secure Sockets Layer) / TLS (Transport Layer Security)

Definition: SSL is a security protocol that provides encrypted communication over a computer network. TLS is its updated, more secure version.
Key Points:

• Works between transport and application layers
• Used by HTTPS, SMTP, IMAP, and others
• Ensures encryption, message integrity, and authentication
• Uses X.509 certificates and Public Key Infrastructure (PKI)
  SSL/TLS Handshake Steps:

1. Client Hello – Client sends supported encryption methods
2. Server Hello – Server responds with chosen method and certificate
3. Key Exchange – Client verifies certificate and sends session key
4. Secure Communication – Both sides encrypt data using the session key
   Advantages: Encrypts data; authenticates parties; prevents eavesdropping and tampering.
   Disadvantages: Computational overhead; certificate renewal required.

🧭 Summary Table

Summary:

• HTTP handles web data transfer without encryption.
• HTTPS secures HTTP using SSL/TLS.
• SSH secures remote login and file transfers.
• SSL/TLS provides encryption and authentication for network communication.