Crypto – chapter 16 - noack Introduction to network stcurity Chapter 16 - Stallings

Crypto – chapter 16 - noack IP security overview IPSec provides security at the IP layer Varieties AH – Authentication header Transport mode - AH fits after IP header and covers TCP Tunnel mode – New IP header – AH covers original IP and TCP ESP – Encapsulating security payload Transport mode – ESP authenticates and encrypts TCP Tunnel mode – New IP header – ESP authenticates and encrypts original IP and TCP Modes Transport – end-to-end services – not processed by routers Tunnel – intermediate services – processed by routers and firewalls

Crypto – chapter 16 - noack Components SA – Security association Carried inside AH and ESP Contents Security parameters index – identifier and specification IP destination address – can be real user or firewall/router Security protocol identifier – is this AH or ESP AH – Authentication header Standard header components Security parameters index (from SA) Sequence number Authentication data ESP – Encapsulation security payload Essentially like AH

Crypto – chapter 16 - noack ESP capabilities Encryption algorithms Triple DES RC5 IDEA Three-key triple IDEA CAST Blowfish Authentication algorithms 96-bit MAC Must support HMAC-MD5-96 and HMAC-SHA-1-96 Padding As needed to support block structure and conceal actual payload length

Crypto – chapter 16 - noack Transport and tunneling Transport Authenticates/protects TCP layer This means packets and IP headers are seen IP headers and addresses are not protected Tunneling This allows IP tunnels – for example between parts of an organization Allows VPN’s Multiple layers are possible (iterated tunneling) Individual SA applies to only one layer (AH or ESP)

Crypto – chapter 16 - noack Key distribution Oakley key distribution protocol Based on Diffie-Hellman Non-specific – does not specify formats, just exchanges Diffie-Hellman weaknesses No identity information Subject to person-in-the-middle attack Computationally intensive – vulnerable to clogging attack Oakley improvements Uses cookies to thwart clogging Allows group negotiation Uses nonces to prevent replays Enables, but authenticates Diffie-Hellman

Crypto – chapter 16 - noack Oakley details Groups Actually five methods Modular exponentiation with lengths 768, 1024, 1536 Elliptic curve group over 155 or 185-bit fields with generator specified Nonce usage Used to prevent replay attacks Authentication methods Digital signatures Public key encryption Symmetric-key encryption – requires out-of-band key distribution

Crypto – chapter 16 - noack More Oakley Details Recommended cookie Hashes (MD5) source IP and port, destination same, UDP same, locally generated secret Reasoning Fast, specific, contains local secret Groups (confusing term) Modular exponentiation (768,1024,1536) Elliptic curve (155,185) Authentication methods Digital signatures Public-key encryption Symmetric-key encryption

Crypto – chapter 16 - noack ISAKMP ISAKMP = ISA key management protocol Manages security associations in general Format Header with cookies and next payload pointer Subsequent payloads with next payload pointer Payload types Security association Proposal Transform Key exchange Identification Certificate Hash Signature Nonce Notification Delete SA’s

Crypto – chapter 16 - noack ISAKMP exchange types Exchange types Base 4 messages, establishes SA Identity protection Includes identity verification, 6 messages Authentication only Authentication – agrees on basic SA, 3 messages Aggressive 3 messages – no identity protection Informational 1 message – just SA management