CAPTCHA and Firewalls

Protecting Against Bots and Network Threats

Essential Security Technologies

What is CAPTCHA?

CAPTCHA stands for "Completely Automated Public Turing test to tell Computers and Humans Apart"

Purpose:

Distinguish humans from bots
Prevent automated abuse
Protect against spam
Secure online forms

How CAPTCHA Works

Challenge Presentation: Display task easy for humans
User Response: Human attempts to solve challenge
Verification: System checks if response is correct
Decision: Grant or deny access based on result

Key Principle: Tasks that are easy for humans but difficult for computers

Types of CAPTCHA

Text-based: Distorted characters
Image-based: Object recognition
Audio-based: Sound interpretation
Behavioral: Mouse movement patterns
reCAPTCHA: Google's advanced system

Text-Based CAPTCHA

Method: Display distorted text that users must decipher

Techniques:
• Character distortion
• Background noise
• Color variations
• Font changes
• Line overlays

Example: "K7mP9" displayed as wavy, noisy text

Challenges:

OCR technology improvements
Accessibility issues
User frustration

Image-Based CAPTCHA

Method: Users identify objects or patterns in images

Common Tasks:
• "Select all images with cars"
• "Click on traffic lights"
• "Choose pictures with bicycles"
• "Identify crosswalks"

Advantages:
• Harder for bots to solve
• More engaging for users
• Can adapt difficulty

reCAPTCHA Evolution

v1: Digitize books (text recognition)
v2: "I'm not a robot" checkbox
v3: Invisible, risk-based scoring

reCAPTCHA v3 Features:

No user interaction required
Risk score (0.0 to 1.0)
Machine learning based
Behavioral analysis

CAPTCHA Advantages

Spam Prevention: Blocks automated form submissions
Bot Protection: Prevents automated account creation
DDoS Mitigation: Slows down automated attacks
Data Quality: Ensures human-generated content
Resource Protection: Prevents API abuse

CAPTCHA Challenges

Usability Issues:

User frustration and abandonment
Accessibility barriers
Mobile device difficulties
Time consumption

Technical Challenges:

AI solving capabilities improving
CAPTCHA farms (human solvers)
False positives/negatives
Maintenance overhead

What is a Firewall?

Firewall is a network security device that monitors and controls incoming and outgoing network traffic based on predetermined security rules

Primary Functions:

Traffic filtering and control
Network segmentation
Access policy enforcement
Threat prevention

Types of Firewalls

Packet Filter Firewall
Stateful Inspection Firewall
Application Proxy Firewall
Next-Generation Firewall (NGFW)
Personal Firewall

Packet Filter Firewall

Operation: Examines packets based on header information

Filtering Criteria:
• Source IP address
• Destination IP address
• Source port
• Destination port
• Protocol (TCP, UDP, ICMP)

Example Rule:
ALLOW TCP 192.168.1.0/24 ANY 80
(Allow HTTP from local network)

Limitations:

No application awareness
No connection state tracking
Vulnerable to IP spoofing

Stateful Inspection Firewall

Enhancement: Tracks connection state and context

State Table Information:
• Connection status (NEW, ESTABLISHED, RELATED)
• Sequence numbers
• Window sizes
• Connection duration

Advantage:
Can distinguish between legitimate return traffic and attack attempts

Benefits:

Better security than packet filtering
Prevents TCP hijacking
Tracks UDP "connections"

Application Proxy Firewall

Method: Acts as intermediary between clients and servers

Operation:
Client → Proxy → Internet

• Proxy establishes separate connections
• Inspects application-layer content
• Can modify or block specific content
• Hides internal network structure

Example: Web proxy filtering malicious URLs

Advantages:

Deep packet inspection
Application-specific filtering
Strong security

Next-Generation Firewall (NGFW)

Advanced Features: Combines traditional firewall with additional security functions

NGFW Capabilities:

Application Awareness: Identify and control applications
Intrusion Prevention: Real-time threat detection
User Identity: User-based policies
SSL Inspection: Decrypt and inspect encrypted traffic
Threat Intelligence: Global threat database integration

Personal Firewall

Purpose: Software-based protection for individual devices

Common Features:
• Inbound/outbound traffic control
• Application permissions
• Network profile management
• Real-time alerts
• Stealth mode

Examples:
Windows Firewall, macOS Firewall, iptables

Benefits:

Endpoint protection
Granular application control
User awareness

Firewall Rule Configuration

Firewall Deployment Models

Network Perimeter: Between internal and external networks
DMZ (Demilitarized Zone): Separate public-facing servers
Internal Segmentation: Between network segments
Host-based: On individual devices
Cloud-based: As a service (FWaaS)

Firewall Limitations

What Firewalls Cannot Do:

Protect against internal threats
Stop social engineering attacks
Prevent all malware
Protect against physical access
Guarantee 100% security

Defense in Depth: Firewalls are one layer in a comprehensive security strategy

CAPTCHA vs Firewall Comparison

Aspect	CAPTCHA	Firewall
Purpose	Human verification	Network protection
Target	Bots and automation	Malicious traffic
Layer	Application	Network/Transport
User Impact	Direct interaction	Transparent
Deployment	Web forms/apps	Network perimeter

Integration in Security Architecture

Layered Defense: CAPTCHA + Firewall + other controls
Complementary Protection: Different threat vectors
Risk-Based Approach: CAPTCHA triggered by firewall risk assessment
Monitoring Integration: Correlated logging and analysis

Example: Firewall detects suspicious IP → Triggers stricter CAPTCHA challenges

Implementation Best Practices

CAPTCHA:

Balance security and usability
Provide accessibility options
Monitor solve rates
Use adaptive difficulty
Consider invisible solutions

Firewall:

Follow least privilege principle
Regular rule audits
Monitor and log activities
Keep firmware updated
Test rule changes

Future Developments

AI-Powered Solutions: Smarter threat detection
Behavioral Analysis: User pattern recognition
Invisible Security: Seamless user experience
Cloud Integration: Scalable, managed services
Zero-Trust Networks: Micro-segmentation

Key Takeaways

CAPTCHA distinguishes humans from bots
Firewalls control network traffic flow
Both are essential but not sufficient alone
Integration creates stronger security
Balance security with user experience
Regular monitoring and updates needed

Remember: Effective security requires multiple complementary technologies working together

Thank You

Questions & Discussion

Next: Malicious Software and Threats