Biometric Techniques for Security (CY-503 (A)) - Unit 4 Short Notes

UNIT 4: Network Security Protocols & Infrastructure

1.0 Cryptographic Foundations & Primitives

1.1 Symmetric Encryption

• Principle: Same secret key K is used for both encryption (E_K(P) = C) and decryption (D_K(C) = P). Requires secure key distribution.

• Block vs. Stream Ciphers:

  | Feature | Block Cipher | Stream Cipher | | :--- | :--- | :--- | | Unit | Fixed-size block (e.g., 128 bits) | Continuous stream of bits/bytes | | Operation | Operates on whole block at once | Operates on one bit/byte at a time | | Example | AES, DES | RC4 | | Error Propagation | A bit error affects entire block | A bit error affects only that bit |

• AES (Advanced Encryption Standard):

  • Block Size: 128 bits. Key Sizes: 128, 192, 256 bits.

  • Core Steps (per round for 128-bit key):

    1. SubBytes: Non-linear substitution using S-box.

    2. ShiftRows: Cyclic shift of rows in state matrix.

    3. MixColumns: Mixing columns using matrix multiplication in GF(2⁸).

    4. AddRoundKey: XOR state with round key.

  • Final Round: Omits MixColumns.

  • Key Expansion: Round keys derived from cipher key via Rijndael's key schedule.

• RC4 Stream Cipher:

  • Key Scheduling (KSA): Initialize S array (0-255), permute using secret key K.

  • Pseudo-Random Generation (PRGA): For each byte:

    i = (i + 1) mod 256

    j = (j + S[i]) mod 256

    Swap(S[i], S[j])

    t = (S[i] + S[j]) mod 256

    Keystream Byte = S[t]

  • Ciphertext: C = P ⊕ Keystream.

  [!TIP] Exam Focus: Be prepared to generate first few keystream bytes for a small key (e.g., 5-bit key K = [1,2,3,4,5]). Show full KSA and first 3 PRGA steps.

1.2 Asymmetric Encryption & Digital Signatures

• Principle: Key pair: Public key (PU) for encryption/verify, Private key (PR) for decryption/sign. E_{PU}(P) = C, D_{PR}(C) = P.

• RSA Algorithm (Detailed Steps with p=3, q=11):

  1. Key Generation:

     • Choose primes: p=3, q=11.

     • n = p * q = 33.

     • φ(n) = (p-1)(q-1) = 2 * 10 = 20.

     • Choose e s.t. 1 < e < φ(n) and gcd(e, φ(n)) = 1. Let e=7 (coprime with 20).

     • Compute d such that (d * e) mod φ(n) = 1. (d*7) mod 20 = 1 → d=3 (since 21 mod 20 = 1).

     • Public Key: (e=7, n=33). Private Key: (d=3, n=33).

  2. Encryption: C = P^e mod n. For P=2: C = 2^7 mod 33 = 128 mod 33 = 29.

  3. Decryption: P = C^d mod n. P = 29^3 mod 33 = 24389 mod 33 = 2.

• Digital Signatures (Using Public-Key Cryptography):

  1. Signing: Sender computes S = H(Message)^d mod n (using their private key).

  2. Verification: Receiver computes S^e mod n and compares with H(Message) (using sender's public key).

  • Crucial Importance: Provides Authentication (sender is who they claim), Integrity (message not altered), and Non-Repudiation (sender cannot deny sending).

1.3 Hash Functions & Message Authentication

• Properties of Cryptographic Hash Functions (H):

  • Fixed Output Size: e.g., SHA-512 → 512-bit digest.

  • Efficient Computation: Easy to compute H(M).

  • Pre-image Resistance: Given h, hard to find M s.t. H(M)=h.

  • Second Pre-image Resistance: Given M1, hard to find M2≠M1 s.t. H(M1)=H(M2).

  • Collision Resistance: Hard to find any M1, M2 s.t. H(M1)=H(M2).

• SHA-512 Algorithm (High-Level Steps):

  1. Pre-processing: Pad message to multiple of 1024 bits. Append length (128 bits).

  2. Initialize Hash Values (H0..H7): First 64 bits of fractional parts of sqrt(primes 2..19).

  3. Process Message in 1024-bit Blocks: For each block, expand to 80 words W[0..79].

  4. Compression Function: Update working variables a..h using 80 rounds of operations with constants K[0..79] (from fractional parts of sqrt(primes 2..79)).

  5. Add to Hash Values: H_i = H_i + a..h (mod 2^64).

• Message Authentication Codes (MACs):

  • Concept: Short tag generated from message M and secret key K: T = MAC_K(M). Receiver verifies T' == MAC_K(M).

  • HMAC Algorithm (Detailed):

    HMAC_K(M) = H((K⁺ ⊕ opad) ∥ H((K⁺ ⊕ ipad) ∥ M))

    where K⁺ is key padded to block size, ipad=0x36, opad=0x5C, ∥ is concatenation.

    Why HMAC? Proven secure based on underlying hash function's properties.

• Secure Message Authentication using Hash Functions (Example):

  • Simple (Insecure): T = H(M ∥ K) vulnerable to length extension.

  • Secure (HMAC): As above. Uses two hash invocations and inner/outer pads to prevent attacks.

2.0 Secure Communication Protocols

2.1 SSL/TLS

• SSL Record Protocol Services:

  1. Confidentiality: Using symmetric encryption (e.g., AES).

  2. Integrity: Using MAC (e.g., HMAC-SHA256).

  3. Optional Compression.

• SSL Handshake Protocol (Step-by-Step for TLS 1.2):

  1. ClientHello: Client sends supported cipher suites, protocol version, random R_C.

  2. ServerHello: Server picks cipher suite, sends version, random R_S.

  3. Certificate: Server sends its certificate (with public key).

  4. ServerHelloDone: Server signals end of hello messages.

  5. ClientKeyExchange: Client generates premaster secret, encrypts with server's public key, sends.

  6. ChangeCipherSpec (Client): Client signals subsequent messages will be encrypted.

  7. Finished (Client): Encrypted H(handshake_messages).

  8. ChangeCipherSpec (Server) & Finished (Server): Server does the same.

  • Master Secret: Both derive master_secret = H(premaster_secret ∥ R_C ∥ R_S).

• SSL Connection vs. SSL Session:

  • Session: Established via handshake. Stores security parameters (master secret, cipher suite). Can be resumed to avoid full handshake.

  • Connection: Actual communication channel using session parameters. Multiple connections can reuse one session.

  • Contribution to Web Security: Session resumption reduces latency and computational cost for repeated connections to same server (e.g., loading multiple images).

2.2 Pretty Good Privacy (PGP)

• Working for Email Security:

  1. Signing (Authentication): Sender computes sig = H(Message)^d_sender. Attaches to message.

  2. Encryption (Confidentiality):

     • Generate random session key K_s.

     • Encrypt message with symmetric cipher (e.g., CAST-128): C = E_{K_s}(M).

     • Encrypt K_s with recipient's public key: K_s' = E_{PU_recipient}(K_s).

     • Send (K_s' ∥ C ∥ sig).

  3. Decryption: Recipient uses PR_recipient to get K_s, decrypts C, verifies sig using sender's public key.

• General Format of a PGP Message:

  
  [Tag: PKESK (Public-Key Encrypted Session Key)]
  
  [Tag: SKESK (Symmetric-Key Encrypted Session Key) - optional]
  
  [Tag: SIGNATURE]
  
  [Tag: LITERAL DATA (the encrypted message)]
  
  

  DiagramCANVAS: A block diagram showing PGP message structure with labeled fields: Version, Signature, Session Key Encrypted with Recipient's PK, Symmetrically Encrypted Data, and Literal Data Packet.

2.3 IP Security (IPSec)

• Authentication Header (AH):

  • Provides data origin authentication, integrity, and anti-replay.

  • Does NOT provide confidentiality.

  • Transport Mode: AH protects payload of original IP packet. [Original IP Header (mutable fields=0) ∥ AH ∥ TCP/UDP ∥ Data].

  • Tunnel Mode: AH protects entire original IP packet. [New IP Header ∥ AH ∥ Original IP Header ∥ TCP/UDP ∥ Data]. Used for gateway-to-gateway (VPN).

• Encapsulating Security Payload (ESP):

  • Provides confidentiality, data origin authentication, integrity, and anti-replay.

  • Transport Mode: [Original IP Header (mutable fields=0) ∥ ESP Header ∥ ESP Trailer ∥ ESP Auth ∥ TCP/UDP ∥ Data].

  • Tunnel Mode: [New IP Header ∥ ESP Header ∥ ESP Trailer ∥ ESP Auth ∥ Original IP Header ∥ TCP/UDP ∥ Data].

• IPSec as a Framework: AH and ESP are two separate protocols. Can be used independently or together (e.g., ESP with auth only, or ESP with both encryption & auth). Security Association (SA) is a one-way connection defined by SPI, IP destination, and security protocol (AH/ESP).

3.0 Network Security Infrastructure & Mechanisms

3.1 Intrusion Detection Systems (IDS)

• Intrusion: Any set of actions that attempt to compromise the confidentiality, integrity, or availability of a resource.

• Classification:

  | Feature | Host-based IDS (HIDS) | Network-based IDS (NIDS) | | :--- | :--- | :--- | | Location | On individual host/endpoint | On network segments (sensors) | | Data Source | System logs, file integrity, process activity | Network packets (traffic) | | Detection | Insider threats, file changes, policy violations | External attacks, DoS, scanning | | Diagram |

  DiagramSEARCH: host-based IDS architecture agent on host sending logs to manager
  |
  DiagramSEARCH: network-based IDS sensor on network segment analyzing traffic
  | | Example | OSSEC, Wazuh | Snort, Suricata |

3.2 Firewalls

• Classification/Types:

  1. Packet Filtering Firewall:

     • Operates at Network Layer (OSI L3).

     • Examines header fields (IP src/dst, port, protocol).

     • Uses ACL (Access Control List) rules: ALLOW/DENY [src_ip] [dst_ip] [port] [protocol].

     • Merits: Fast, transparent, low cost.

     • Demerits: No payload inspection, susceptible to IP spoofing, complex rule management.

  2. Circuit-Level Gateway:

     • Operates at Session Layer (OSI L5).

     • Monitors TCP handshake (SYN, SYN-ACK, ACK) to validate sessions.

     • Hides internal network addresses (NAT-like).

     • Merit: Simple, good for outbound control.

     • Demerit: No inspection of data within session.

  3. Application-Level Gateway (Proxy Firewall):

     • Operates at Application Layer (OSI L7).

     • Intercepts all traffic for specific application (HTTP, FTP). Acts as intermediary.

     • Performs deep packet inspection and protocol validation.

     • Merits: Highest security, detailed logging, user authentication.

     • Demerits: Performance bottleneck, must support each application, expensive.

• Role of IDS & Firewalls Against Malware:

  • Firewall: Blocks unauthorized connections/ports (preventative). Can block known malicious IPs/domains.

  • IDS: Detects malware activity (e.g., beaconing, exploit traffic, policy violation). Does not block (unless IPS). Provides alerts and forensic data.

  • Complementary: Firewall reduces attack surface; IDS detects what gets through or originates internally.

3.3 Virtual Private Networks (VPN)

• What is a VPN? A tunnel over a public network (Internet) that provides confidentiality, authentication, and integrity for private traffic, making it appear as if hosts are on a private network.

• Types of VPNs:

  • Remote Access VPN: Individual user → corporate network (e.g., employee from home). Uses protocols like PPTP, L2TP/IPsec, SSL-VPN.

  • Site-to-Site (Gateway-to-Gateway) VPN: Connects entire networks (e.g., branch offices). Uses IPsec or GRE.

• Comparison with Trusted Operating Systems:

  | Aspect | VPN | Trusted OS (e.g., SELinux, Trusted Solaris) | | :--- | :--- | :--- | | Primary Goal | Secure communication channel over untrusted network. | Secure individual host/system via mandatory access control (MAC). | | Security Scope | Network/Transport layer (tunneling). | OS/Kernel level (process, file, resource access). | | Key Mechanism | Encryption (IPsec, SSL), Tunneling. | Security policy, labels, reference monitor. | | Application | Connect remote users/sites. | Protect high-security servers, prevent insider threats. | | Example | Cisco AnyConnect, OpenVPN. | SELinux enforcing mode, Microsoft Windows Integrity Mechanism. |

3.4 Malicious Software (Malware)

• Types & Infiltration Methods:

  | Malware Type | Core Behavior | Infiltration/Propagation | | :--- | :--- | :--- | | Virus | Attaches to legitimate program/file. Requires user execution. | Email attachments, infected USB, downloads. | | Worm | Self-replicating, spreads autonomously over network. | Exploits vulnerabilities (e.g., SMB), email, P2P. | | Trojan Horse | Disguised as legitimate software. Contains hidden malicious function. | Social engineering, fake downloads, cracked software. | | Rootkit | Hides existence/activities of other malware. Deep OS integration. | Exploits, trojans, phishing. | | Ransomware | Encrypts files, demands ransom. | Phishing, exploit kits, RDP brute-force. | | Spyware/Adware | Collects user data/displays ads. | Bundled with freeware, drive-by downloads. | | Bot/Botnet | Compromised host under remote control (C&C). | Worm/virus/trojan infection, then join botnet. |

• IDS/Firewall Safeguarding:

  • Firewall: Blocks command-and-control (C&C) callbacks (known bad IPs/domains), prevents worm propagation by blocking exploit ports.

  • IDS: Detects anomalous traffic patterns (e.g., mass emailing from virus, worm scanning, C&C communication). Signature-based IDS can detect known malware payloads.

4.0 Wireless & Mobile Security

4.1 Wireless LAN (WLAN) Security

• Security Challenges:

  • Open Medium: Radio signals propagate beyond physical boundaries.

  • No Physical Control: Attacker can be anywhere within range.

  • Weak/default Configurations: Often overlooked.

  • Eavesdropping: Easy to capture traffic.

  • Rogue Access Points: Unauthorized APs inside network.

  • Client Misassociation: Clients connecting to evil twin APs.

• WLAN Security Mechanisms:

  • WEP (Wired Equivalent Privacy): Broken. Uses RC4 with static key. IV reuse → key recovery.

  • WPA/WPA2/WPA3:

    • WPA (TKIP): Temporary fix. Per-packet key mixing, MIC.

    • WPA2 (CCMP/AES): Mandatory for Wi-Fi certification. Uses AES in CCM mode (confidentiality+integrity). Still vulnerable to KRACK (key reinstallation attack).

    • WPA3 (SAE - Simultaneous Authentication of Equals): Replaces PSK with Dragonfly handshake. Provides forward secrecy and resistance to offline dictionary attacks.

  • 802.1X (Port-Based Network Access Control):

    • Framework: Supplicant (client) → Authenticator (AP) → Authentication Server (RADIUS).

    • Process: EAPOL (EAP over LAN) frames. Authenticator blocks port until supplicant authenticated.

    • Provides individual user authentication (vs. pre-shared key for all).

• Access Point Security in Public Networks:

  • Use Enterprise WPA2/WPA3 with 802.1X. Avoid open or WPA2-Personal (PSK) hotspots.

  • Client-Side: Use VPN for all traffic. Ensure OS firewall enabled. Disable auto-connect.

  • AP Configuration: Use strong RADIUS backend, disable WPS, use separate guest VLAN.

4.2 Wireless Application Protocol (WAP) Security

• WAP Architecture (Layered):

  
  Application Layer (WAE - Wireless Application Environment)
  
  Session Layer (WSP - Wireless Session Protocol)
  
  Transaction Layer (WTP - Wireless Transaction Protocol)
  
  Security Layer (WTLS - Wireless Transport Layer Security)
  
  Transport Layer (WDP - Wireless Datagram Protocol) → underlying bearers (SMS, GPRS, etc.)
  
  

  DiagramCANVAS: A 5-layer stack diagram from top (WAE) to bottom (WDP), with WTLS in the middle highlighted as the security layer.

• WTLS (Wireless Transport Layer Security):

  • Purpose: Provide security (privacy, authentication, integrity) for WAP traffic over unreliable wireless bearers (high latency, low bandwidth).

  • Based on TLS 1.1 but optimized: Handles datagram (UDP-like) nature of WDP. Smaller record sizes, optional retransmission.

  • Key Features: Supports cryptographic algorithms suitable for constrained devices (e.g., RSA, DSA, HMAC, RC5, DES, 3DES, AES). Supports session resumption.

• Role in Securing Wireless Comms: WTLS secures the wireless leg (handset to WAP gateway). However, the gateway decrypts WTLS and re-encrypts with standard TLS/TCP for the wired Internet. This creates a decryption point.

• Security Issues/Challenges in WTLS:

  1. WTLS-to-TLS Gap: Traffic is decrypted at the WAP gateway. If gateway is compromised, end-to-end security is broken.

  2. Algorithm Limitations: Early implementations used weak crypto (e.g., 40-bit RC5) for export compliance.

  3. Implementation Flaws: Vulnerabilities in gateway software.

  4. End-to-End Problem: WTLS does not provide true end-to-end security between client and final web server; it's hop-by-hop to the gateway.

5.0 Specialized Security Applications

5.1 Secure Electronic Transaction (SET)

• Main Security Concerns in Online Financial Transactions:

  • Confidentiality: Cardholder data (PAN) must not be exposed to merchant.

  • Integrity: Order and payment info must not be altered.

  • Authentication: Customer, merchant, and bank must authenticate each other.

  • Non-Repudiation: Customer cannot deny placing order; merchant cannot deny received payment.

• How SET Addresses These Concerns:

  1. Dual Signature: Customer signs a hash of Order Info + Payment Info together. Merchant sees order, bank sees payment. Neither gets both.

  2. Three-Party Model: Customer, Merchant, Bank (Acquirer & Issuer via payment gateway).

  3. Certificates: All parties have X.509 v3 certificates.

  4. Key Exchange: Uses symmetric key for transaction (efficiency) encrypted with public keys.

• Application in Business Environment (Example):

  • Customer: browses merchant site, places order. Uses SET wallet software. Generates dual signature.

  • Merchant: Receives order info, dual signature. Forwards payment info (encrypted for bank) and dual signature to payment gateway.

  • Bank (Issuer): Verifies customer's certificate and signature. Authorizes payment. Sends confirmation to merchant via gateway.

  • Merchant: Fulfills order upon receiving bank confirmation.

  • Outcome: Customer's card number never revealed to merchant. Bank authenticates customer directly.

5.2 Biometric Authentication

• Principles: Use of unique, measurable biological or behavioral characteristics for automated recognition.

• Process (Generic):

  1. Enrollment: Capture raw biometric → extract feature vector → store in database (often as template, not raw image).

  2. Live Capture: Capture new sample.

  3. Feature Extraction: Extract feature vector from live sample.

  4. Matching: Compare live feature vector against stored template(s). Compute similarity score.

  5. Decision: If score > threshold → accept; else → reject.

• Types:

  • Physiological: Fingerprint, Iris, Face, DNA, Hand geometry.

  • Behavioral: Voice, Signature dynamics, Keystroke dynamics, Gait.

• Key Metrics:

  • False Acceptance Rate (FAR): Probability of accepting impostor.

  • False Rejection Rate (FRR): Probability of rejecting genuine user.

  • Equal Error Rate (EER): Point where FAR=FRR. Lower EER = better system.

• Context with Smart Cards: Often used in two-factor authentication: "something you have" (smart card) + "something you are" (biometric). Biometric template can be stored on smart card (personalization) or in central database.

6.0 Web & Application Layer Security Approaches

6.1 Web Traffic Security

• General Approaches:

  1. SSL/TLS: De facto standard for securing HTTP (HTTPS). Provides end-to-end encryption between browser and web server.

  2. VPN (SSL-VPN, IPsec): Secures entire IP traffic, including web, from remote client to corporate network gateway.

  3. Application-Layer Gateways/Proxies: Reverse proxies (e.g., for DDoS protection, WAF) that terminate and re-encrypt TLS.

  4. HTTP Strict Transport Security (HSTS): Forces browser to use HTTPS only.

  5. Secure Cookies: Secure and HttpOnly flags.

6.2 Parameter Pattern Matching

• Concept: A signature-based detection technique, often used in Web Application Firewalls (WAFs) and Intrusion Prevention Systems (IPS).

• How it works:

  1. Define patterns (regular expressions, byte sequences) that characterize known attacks (e.g., SQL injection: ' OR 1=1--, XSS: <script>).

  2. Inspect HTTP request parameters (GET/POST data, cookies, headers) for these patterns.

  3. If a match is found → block request and log event.

• Limitations: Easily evaded by obfuscation (e.g., UNION/**/SELECT), encoding (URL, HTML, Unicode), or zero-day attacks (no known pattern). Requires constant signature updates.