🔄 What We Covered

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Layer 1: Physical Security

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• Cable tapping and physical access
• Environmental threats
• Facility security controls

Layer 2: Data Link Security

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• MAC spoofing and flooding
• VLAN security
• Wireless network protection

Layer 3: Network Security

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• IP spoofing and routing attacks
• IPSec implementation
• Network segmentation

Layer 4: Transport Security

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• TCP/UDP vulnerabilities
• SYN flood protection
• Port-based security

🎯 Today’s Focus

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Upper layer security and end-to-end protection

💬 Session Layer Overview

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🎯 Core Functions

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• Session establishment and termination
• Dialog control (duplex management)
• Session checkpointing and recovery
• Session synchronization
• Token management for exclusive access

🔧 Key Responsibilities

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• Manage conversations between applications
• Coordinate data exchange
• Handle session failures and recovery
• Provide synchronization points

📋 Session Types

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• Simplex - One-way communication
• Half-duplex - Two-way, alternating
• Full-duplex - Simultaneous two-way

🚨 Session Layer Threats

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🎭 Session Management Attacks

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• Session hijacking - Taking over active sessions
• Session fixation - Forcing known session IDs
• Session replay - Reusing captured sessions
• Cross-site request forgery (CSRF)
• Session timeout exploitation

🔓 Authentication Bypass

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• Session token prediction
• Weak session management
• Concurrent session abuse
• Session state manipulation

📊 Session Information Disclosure

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• Session ID leakage in URLs
• Unencrypted session data
• Session storage vulnerabilities
• Cross-domain session sharing

🔒 Session Security Best Practices

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🎯 Secure Session Management

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• Strong session ID generation
• Session expiration policies
• Secure session storage
• Session invalidation on logout
• Concurrent session control

🔐 Session Token Security

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import secrets
import hashlib
import time

def generate_secure_session_id():
    # Cryptographically secure random generation
    random_part = secrets.token_hex(16)
    timestamp = str(int(time.time()))
    user_info = get_user_context()
    
    # Combine with server secret
    session_data = f"{random_part}:{timestamp}:{user_info}"
    session_id = hashlib.sha256(session_data.encode()).hexdigest()
    
    return session_id

⏰ Session Lifecycle Management

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• Creation with strong entropy
• Validation on each request
• Renewal for long sessions
• Destruction on logout/timeout

🛡️ Session Protection Mechanisms

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🔧 Technical Controls

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• HTTPS-only session cookies
• HttpOnly flag prevents XSS access
• Secure flag for encrypted transmission
• SameSite attribute for CSRF protection
• Session binding to IP/User-Agent

📊 Session Monitoring

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// Session anomaly detection
class SessionMonitor {
    detectAnomalies(sessionData) {
        const anomalies = [];
        
        // IP address changes
        if (sessionData.currentIP !== sessionData.originalIP) {
            anomalies.push('IP_CHANGE');
        }
        
        // Unusual access patterns
        if (sessionData.requestRate > THRESHOLD) {
            anomalies.push('HIGH_RATE');
        }
        
        // Concurrent sessions
        if (sessionData.concurrentSessions > MAX_SESSIONS) {
            anomalies.push('TOO_MANY_SESSIONS');
        }
        
        return anomalies;
    }
}

🎨 Presentation Layer Overview

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🎯 Core Functions

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• Data format translation
• Encryption and decryption
• Data compression
• Character encoding conversion
• Data structure formatting

🔄 Data Transformations

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• ASCII/Unicode encoding
• Image/Video format conversion
• Compression algorithms (ZIP, GZIP)
• Serialization (JSON, XML, Binary)
• Protocol buffer encoding

🔒 Security Services

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• Symmetric encryption (AES, 3DES)
• Asymmetric encryption (RSA, ECC)
• Digital signatures
• Certificate management
• Key exchange protocols

⚠️ Presentation Layer Threats

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🔓 Encryption Weaknesses

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• Weak cryptographic algorithms
• Poor key management
• Implementation vulnerabilities
• Side-channel attacks
• Cryptographic oracle attacks

📄 Data Format Attacks

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• XML injection attacks
• JSON parsing vulnerabilities
• Serialization attacks
• Buffer overflow in parsers
• Zip bomb attacks

🎭 Protocol Manipulation

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• SSL stripping attacks
• Downgrade attacks
• Certificate spoofing
• Man-in-the-middle TLS
• Compression attacks (CRIME, BREACH)

🔐 TLS Handshake Process

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sequenceDiagram
    participant C as Client
    participant S as Server
    
    C->>S: ClientHello (versions, ciphers, random)
    S->>C: ServerHello (chosen cipher, random)
    S->>C: Certificate (server cert)
    S->>C: ServerHelloDone
    
    C->>S: ClientKeyExchange (pre-master secret)
    C->>S: ChangeCipherSpec
    C->>S: Finished (encrypted)
    
    S->>C: ChangeCipherSpec
    S->>C: Finished (encrypted)
    
    Note over C,S: Secure Communication

🔍 Security Features

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• Server authentication via certificates
• Data encryption with symmetric keys
• Data integrity with MAC
• Perfect forward secrecy

🛡️ TLS Security Best Practices

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📊 Cipher Suite Selection

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Recommended Ciphers:
  - TLS_AES_256_GCM_SHA384 (TLS 1.3)
  - TLS_CHACHA20_POLY1305_SHA256 (TLS 1.3)
  - TLS_AES_128_GCM_SHA256 (TLS 1.3)
  - ECDHE-RSA-AES256-GCM-SHA384 (TLS 1.2)
  - ECDHE-RSA-CHACHA20-POLY1305 (TLS 1.2)

Avoid:
  - RC4 (broken)
  - 3DES (weak)
  - MD5 (collision attacks)
  - Export ciphers (weak)

🔧 Implementation Security

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• Strong certificate validation
• Certificate pinning for mobile apps
• HSTS (HTTP Strict Transport Security)
• OCSP stapling for revocation
• Regular certificate rotation

🚨 Common TLS Vulnerabilities

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• POODLE - SSL 3.0 padding oracle
• BEAST - CBC cipher vulnerability
• HEARTBLEED - OpenSSL buffer overflow
• FREAK - Export cipher downgrade

🌐 Application Layer Overview

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🎯 Core Functions

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• User interface to network services
• Application protocols (HTTP, SMTP, FTP)
• Data presentation to users
• Network service access
• Application-specific logic

📋 Common Protocols

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• HTTP/HTTPS - Web browsing
• SMTP/POP/IMAP - Email services
• FTP/SFTP - File transfer
• DNS - Name resolution
• DHCP - IP configuration
• SNMP - Network management

🔧 Application Types

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• Web applications
• Email clients
• File transfer tools
• Remote access applications
• Network management tools

🚨 Application Layer Threats

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🌐 Web Application Attacks

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• SQL injection - Database manipulation
• Cross-site scripting (XSS)
• Cross-site request forgery (CSRF)
• Remote code execution (RCE)
• File inclusion vulnerabilities

📧 Email-Based Attacks

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• Phishing and spear phishing
• Email spoofing
• Malware attachments
• Business email compromise (BEC)
• Email bombing

🔍 Protocol-Specific Attacks

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• HTTP response splitting
• DNS poisoning
• FTP bounce attacks
• SMTP relay abuse
• SNMP community string attacks

🔝 OWASP Top 10 (2021)

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1. A01: Broken Access Control

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• Vertical privilege escalation
• Horizontal privilege escalation
• Missing access controls
• CORS misconfigurations

2. A02: Cryptographic Failures

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• Weak encryption algorithms
• Poor key management
• Unencrypted sensitive data
• Weak random number generation

3. A03: Injection

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• SQL injection
• NoSQL injection
• LDAP injection
• Command injection

4. A04: Insecure Design

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• Threat modeling gaps
• Secure design principles ignored
• Missing security controls

5. A05: Security Misconfiguration

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• Default credentials unchanged
• Unnecessary features enabled
• Missing security headers
• Verbose error messages

6. A06: Vulnerable Components

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• Outdated libraries
• Known vulnerabilities
• Unsupported components

7. A07: Authentication Failures

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• Weak password policies
• Session management flaws
• Brute force vulnerabilities

8. A08: Software Integrity Failures

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• Untrusted sources
• Missing integrity checks
• Supply chain attacks

9. A09: Logging/Monitoring Failures

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10. A10: Server-Side Request Forgery

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🔍 Input Validation Principles

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🎯 Validation Strategies

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• Allow-list (whitelist) approach
• Input sanitization
• Length restrictions
• Type validation
• Format validation
• Boundary checking

📊 Common Input Sources

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• User forms and fields
• URL parameters
• HTTP headers
• Cookies
• File uploads
• API requests

✅ Validation Best Practices

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• Server-side validation (never trust client)
• Early validation at entry points
• Consistent validation across application
• Error handling without information leakage

🛡️ SQL Injection Prevention

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❌ Vulnerable Code

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// DON'T DO THIS - SQL Injection vulnerable
$username = $_POST['username'];
$password = $_POST['password'];

$query = "SELECT * FROM users WHERE username = '$username' 
          AND password = '$password'";
$result = mysql_query($query);

// Attacker input: username = admin' --
// Result: SELECT * FROM users WHERE username = 'admin' --

✅ Secure Implementation

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// Secure approach using prepared statements
$stmt = $pdo->prepare("SELECT * FROM users WHERE username = ? 
                       AND password = ?");
$stmt->execute([$username, $hashed_password]);
$result = $stmt->fetch();

// Additional validation
function validateInput($input, $type) {
    switch($type) {
        case 'username':
            return preg_match('/^[a-zA-Z0-9_]{3,20}$/', $input);
        case 'email':
            return filter_var($input, FILTER_VALIDATE_EMAIL);
    }
}

🎭 Types of XSS Attacks

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1. Reflected XSS

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• User input reflected in response
• Immediate execution
• Social engineering required
• URL-based attacks

2. Stored XSS

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• Malicious script stored on server
• Persistent across sessions
• Affects multiple users
• Most dangerous type

3. DOM-based XSS

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• Client-side code vulnerability
• JavaScript manipulation
• No server involvement
• Difficult to detect

🛡️ XSS Prevention Techniques

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🔒 Output Encoding

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// HTML Entity Encoding
function htmlEncode(str) {
    return str.replace(/[&<>"']/g, function(match) {
        return {
            '&': '&amp;',
            '<': '&lt;',
            '>': '&gt;',
            '"': '&quot;',
            "'": '&#x27;'
        }[match];
    });
}

// Safe DOM manipulation
const safeDiv = document.createElement('div');
safeDiv.textContent = userInput; // Safe - no HTML parsing
document.body.appendChild(safeDiv);

🔧 Security Headers

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Content-Security-Policy: default-src 'self'; 
    script-src 'self' 'unsafe-inline'
X-XSS-Protection: 1; mode=block
X-Content-Type-Options: nosniff
X-Frame-Options: DENY

📊 Input Validation

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• Allow-list of safe characters
• Length restrictions
• Context-aware encoding
• Regular expression validation

🏗️ Security Architecture Patterns

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🛡️ Defense in Depth

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graph TB
    A[Web Application Firewall] --> B[Load Balancer]
    B --> C[Web Server]
    C --> D[Application Server]
    D --> E[Database Server]
    
    F[Network Firewall] --> A
    G[DDoS Protection] --> F
    
    style A fill:#e3f2fd
    style C fill:#f3e5f5
    style D fill:#e8f5e8
    style E fill:#fff3e0

🔒 Zero Trust Model

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• Never trust, always verify
• Least privilege access
• Microsegmentation
• Continuous monitoring
• Context-aware access

📊 Secure Development Lifecycle

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• Security requirements gathering
• Threat modeling
• Secure coding practices
• Security testing
• Deployment security

🔧 Application Security Controls

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🎯 Preventive Controls

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• Input validation
• Output encoding
• Authentication mechanisms
• Authorization systems
• Secure communications (HTTPS)

🔍 Detective Controls

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• Application monitoring
• Log analysis
• Intrusion detection
• Vulnerability scanning
• Security information correlation

🚨 Corrective Controls

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• Incident response procedures
• Backup and recovery
• Patch management
• Configuration management
• Emergency procedures

📈 Security Metrics

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• Vulnerability density
• Time to patch
• Authentication success rates
• Security incident frequency
• User security awareness

🔗 End-to-End Security

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📊 Multi-Layer Protection Matrix

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🎯 Security Integration Principles

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• Complementary controls at each layer
• Consistent security policies
• Coordinated incident response
• Unified monitoring and management

🛡️ Comprehensive Security Strategy

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📋 Security Architecture Checklist

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• Physical security perimeter
• Network segmentation and firewalls
• Secure protocols (TLS, IPSec)
• Strong authentication and authorization
• Input validation and output encoding
• Security monitoring and logging
• Incident response procedures
• Regular security assessments

🔄 Continuous Security Process

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graph LR
    A[Plan] --> B[Implement]
    B --> C[Monitor]
    C --> D[Assess]
    D --> E[Improve]
    E --> A
    
    style A fill:#e3f2fd
    style B fill:#f3e5f5
    style C fill:#e8f5e8
    style D fill:#fff3e0
    style E fill:#fce4ec

💡 Success Factors

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• Executive support
• Security awareness training
• Regular updates and patches
• Third-party risk management
• Compliance monitoring

❌ Frequent Errors

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Layer-Specific Mistakes

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• Physical: Ignoring environmental security
• Data Link: Default VLAN configurations
• Network: Overly permissive firewall rules
• Transport: Ignoring UDP security
• Session: Weak session management
• Presentation: Weak encryption implementation
• Application: Insufficient input validation

Integration Problems

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• Security gaps between layers
• Inconsistent policies across layers
• Poor monitoring coordination
• Inadequate incident response integration

✅ Best Practices

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Design Principles

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• Start with physical security foundation
• Build security into each layer
• Implement defense in depth
• Regular security assessments
• Staff training on all layers

Implementation Guidelines

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• Document security architecture
• Test security controls regularly
• Monitor all layers continuously
• Update security controls as needed
• Integrate with business processes

Success Metrics

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• Reduced security incidents
• Faster incident detection
• Improved compliance
• Lower security costs
• Better user experience

🔜 Lecture 7: Introduction to Cryptography

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🎯 Focus Topics:

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• Cryptography fundamentals
• Symmetric encryption algorithms
• Asymmetric encryption systems
• Key management principles
• Digital signatures and certificates
• Cryptographic applications

📝 Preparation Tasks:

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• Review mathematical basics (modular arithmetic)
• Research historical encryption methods
• Think about data protection needs
• Consider key distribution challenges

🎓 Key Takeaways Today

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OSI Upper Layers Security

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• Session layer manages communication state
• Presentation layer handles encryption and data formats
• Application layer faces the most diverse threats
• Integration across all layers is essential

Critical Security Concepts

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• Defense in depth applies to network architecture
• Each layer has unique security responsibilities
• Application security requires comprehensive approach
• End-to-end security needs all layers working together