Secure Programming

Networking

• Port 54711
  • Used for TCP and UDP protocols
  • Ensures delivery of data packets
• Port 443
  • Used for secure web traffic via HTTPS
  • Encrypted transmission
  • Uses SSL/TLS encryption to protect data
  • Vital for information such as passwords or credit card details

Port	Protocol / Service	Description
21	FTP	File Transfer Protocol
22	SSH	Secure remote login and command-line access
23	Telnet	Unsecure remote login
25	SMTP (Simple Mail Transfer Protocol)	Sending emails between mail servers
53	DNS (Domain Name System)	Translates domain names to IP addresses
80	HTTP (Hyper Transfer Protocol)	Web page transfer
110	POP3 (Post Office Protocol v3)	Email retrieval (downloads and often deletes from the server)
123	NTP (Network Time Protocol)	Network time synchronization
143	IMAP (Internet Message Access Protocol)	Email retrieval (keeps emails on the server)
443	HTTPS (HTTP Secure)	Secure web page transfer
3389	RDP (Remote Desktop Protocol)	Remote Desktop access

IP Address: CIDR

• IP Address is a unique numerical identifier assigned to every device connected to a computer network
• Two types
  • v4 (32 bits): 192.168.0.1
  • v6 (128 bits): 2001:0db8:85a3:0000:0000:8a2e:0370:f928
• Classless Inter-Domain Routing
  • allocating IP addresses and routing internet traffic
  • used for firewalls, routing tables, etc
• 192.168.5/24 <- indicate the first 24 bits are network ID
  • Last 8 bits are hosts
• Lookback Address
  • 127.0.0.0/8 (127.0.0.1 -- localhost)
• ISPs use a protocol called Dynamic Host Configuration Protocol (DHCP)
  • automatically assign IP addresses to devices (using leases)
  • You can also request a static IP

DNS

• translates to human readable text rather than numbers
• DNS Lookup tools
  • allow to query DNS directly and examine responses
• (IP address, Port)

Servers and Clients

• Servers wait for network connections (and respond with data)
  • One machine can run alot of servers, each at a different port
  • Generally provide a service
• Clients to connect and request
  • Browsers
  • SSH
  • telnet
• curl - can make http requests for you
• telnet - establishing text based communication with a remote computer or server

Web Server Responses

• static
  • html
  • css
  • jpg
• dynamic
  • generated on the fly
  • python
  • node
  • leverage database to organize and query data that populates the dynamic data

Delivery method

• Streams (TCP)
  • make sure data arrives complete, in order without errors
  • used when reliability is important
  • http / https
  • ssh
• Discrete messages (UDP)
  • send data quickly
  • some bits maybe lost or out of order
  • used when speed is more important
  • streaming movies
  • dns

Flask Server Hello World

# import library 
from flask import Flask 

# initialize
app Flask(__name__)

# a route
@app.route("/")
def hello_world():
	return "<p>Hello, World!</p>" # serve html

app.run() # run the server