IPsec Protocols and Security Mechanisms

Network Security: IP Security

• The presentation covers IP security, specifically IPsec, at the University of Bern.
• The course instructor is Prof. Dr. Torsten Braun from the Institute for Informatics.
• The presentation dates are November 4th-11th, 2024.

IPsec Overview

• Architecture (RFC 1636): Issued in 1994 by the Internet Architecture Board, this aims to secure network infrastructure from unauthorized monitoring, control of network traffic, and end-user-to-end-user traffic using authentication and encryption.
• Goals: Securing network infrastructure, unauthorized monitoring and control, end-user-to-end-user traffic using authentication and encryption.
• Design: IPv6 and IPv4 support. IPsec specification now part of Internet standards.
• Document detail: Includes general concepts, security requirements, definitions, and mechanisms defining IPsec technology. Provides message authentication (RFC 4302). Encapsulating Security Payload (ESP) is the preferred method in modern uses, deprecating Authentication Header (AH).

IPsec Applications

• IPsec supports communications over LANs, public WANs, and the internet and it encrypts or authenticates all traffic at the IP layer.
• Example uses: Secure branch office connectivity, virtual private networks (VPNs), secure remote access to ISPs/companies, and establishing extranets/intranets.

IPsec Applications (in IP-related protocols)

• Mobile IP, routing protocols, address resolution, and ICMP.

IPsec Services (RFC 4301)

• Select required security protocols, determine algorithms for services, put cryptographic keys in place to provide requested services.
• RFC 4301 services: Access control, connectionless integrity, data origin authentication, replayed packet rejection, confidentiality(encryption), and limited traffic flow confidentiality.

IPsec Policy (Architecture)

• Uses IKEv2 for key exchange
• Includes Security Policy Database (SPD), Security Association Database (SAD).
• IPsecv3 and IPsec SA Pair, and ESP.

Security Association (SA)

• Parameters:
• Security Parameter Index (SPI), Sequence number counter, Sequence counter overflow, Anti-replay window, AH information, ESP information, SA Lifetime, IPsec protocol mode, Path MTU.
• Destination Address: The address of the SA's destination endpoint.
• Security Protocol Identifier: Identifies whether association is AH or ESP for security association.

Security Policy Database (SPD)

• SPD links IP traffic to specific security associations, using selections of IP and upper layer protocol field values.
• Used to filter outgoing traffic to map traffic to a particular SA for processing.
• In complex environments, multiple SPDs may relate to one SA.

Selectors Determining SPD Entry (various)

• Remote IP Address (single, list, range, wildcard).
• Local IP Address (single, list, range, wildcard).
• Port.
• Next Layer Protocol (e.g. IPv4/IPv6, TCP/UDP).

IPsec Output Processing

• The flow describes how IP packets are determined and processed based on matching the search criteria between the incoming packets and the SPD database.
• Packet matching procedures with possible outcomes: BYPASS, DISCARD, PROTECT.

IPsec Input Processing

• The input processing flow outlines how inbound IP packets are handled, similar to outbound processing.
• Packet matching procedures with possible outcomes: BYPASS, DISCARD, Processing (AH/ESP), Match.

Encapsulation Security Payload (ESP)

• Packet Format: Includes Optional Initialization Vector (IV), padding, SPI, sequence number, payload data, integrity check value, and encryption.

Anti-Replay Attack Service

• By using sequence number, duplicate authenticated IP packets are prevented from harming services.
• If a packet's sequence number falls within the defined window, processing proceeds as follows:
• Check MAC (Message Authentication Code).
• Advance the window, Mark the sequence number is received.
• If packet is left of window or Auth fail, Discard the packet.

Encapsulation Security Payload (ESP)

• Transport Mode: Outer IP header remains unchanged. Encryption occurs between host and the security gateway.
• Tunnel Mode: Inner IP header is encapsulated (changed). Encryption occurs solely between security gateways.

Virtual Private Networks (VPNs)

• Tunnel mode in ESP can be used to create private networks within public networks, traffic can only move from one VPN to another.
• VPNs are used to create Wide Area Networks (WAN) across geo areas which allow site-to-site connections to branch offices and connections for mobile users to company LAN's.

Authentication Header (AH)

• Authentication of all Immutable IP fields between sender and receiver. Uses keyed MD5 to generate 128-bit authentication data.

Authentication Header (AH)

• Transport Mode: Attaches AH to the existing IP packet.
• Tunnel Mode: AH is put in a new IP packet to encapsulate the existing data.
• AH protecting only IP header, ESP for beyond IP header including export issues.

Combining Security Associations

• Transport Adjacency: Applying multiple security associations (SAs) to a single IP packet without tunneling.
• Iterated Tunneling: Using multiple layers of security protocols through IP tunneling. Supports multiple levels of nested security.
• Authentication and Confidentiality (ESP): Applying ESP to data for protection, then authentication data for ciphertext (not plaintext).
• Transport-Tunnel Bundle: Applying authentication before encryption between two hosts, and using a combined inner AH and outer ESP SA.

Internet Key Exchange (IKE)

• Key Management Types:
• Manual (administrator configurations each system with related system keys).
• Automated (System automatically generates keys based on need/request.)
• Key determination protocol: Refinement of Diffie-Hellman key exchange.
• Clogging Attack: Attackers forge source addresses and send public keys to victim to consume its resources.
• IKE Key Determination: Uses cookies to thwart clogging attacks, enables exchange of DH public keys, and authenticates the exchange to prevent man-in-the-middle attacks.
• Cookie Exchange: Each side provides a pseudorandom number in the initial message for authentication
• Cookie Generation Requirements: Cookies are specific to parties, cannot be generated by anyone else, authentication is fast, and is not deducible to secret data.
• IKEv2 Exchanges: This contains the information on exchanges between initiator and responder. Initial exchanges and CREATE_CHILD_SA Exchange and Informational Exchange are listed.

IKE Formats

• SPI definitions (Initiator and Responder)
• Next payload, MjVer, MnVer, Exchangetype, Message ID, Length (in IKE headers).
• Generic payload header (bits, Next payload, Reserved, Payload length).

IKE Payload Types

• Provides a table of Security Association, Key Exchange, Identification, Certificates, Requests, Authentication, Nonce, Notify, Delete, Vendor ID and their relevant Proposals and Parameters.