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CSC 474 Information Systems Security. Topic 4.2: IPsec. Outline. IPsec Objectives IPsec architecture & concepts IPsec authentication header IPsec encapsulating security payload. IPsec Objectives. Why do we need IPsec? IP V4 has no authentication IP spoofing

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CSC 474 Information Systems Security


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csc 474 information systems security

CSC 474Information Systems Security

Topic 4.2: IPsec

Dr. Peng Ning

outline
Outline
  • IPsec Objectives
  • IPsec architecture & concepts
  • IPsec authentication header
  • IPsec encapsulating security payload

Dr. Peng Ning

ipsec objectives
IPsec Objectives
  • Why do we need IPsec?
    • IP V4 has no authentication
      • IP spoofing
      • Payload could be changed without detection.
    • IP V4 has no confidentiality mechanism
      • Eavesdropping
    • Denial of service (DOS) attacks
      • Cannot hold the attacker accountable due to the lack of authentication.

Dr. Peng Ning

ipsec objectives cont d
IPsec Objectives (cont’d)
  • IP layer security mechanism for IPv4 and IPv6
    • Not all applications need to be security aware
    • Can be transparent to users
    • Provide authentication and confidentiality mechanisms.

Dr. Peng Ning

ipsec architecture
IPsec Architecture

IPsec module 1

IPsec module 2

SPD

SPD

IKE

IKE

IPsec

SAD

SAD

IPsec

SA

SPD: Security Policy Database; IKE: Internet Key Exchange;

SA: Security Association; SAD: Security Association Database.

Dr. Peng Ning

ipsec architecture cont d
IPsec Architecture (Cont’d)
  • Two Protocols (Mechanisms)
    • Authentication Header (AH)
    • Encapsulating Security Payload (ESP)
  • IKE Protocol
    • Internet Key Management

Dr. Peng Ning

ipsec architecture cont d1
IPsec Architecture (Cont’d)
  • Can be implemented in
    • Host or gateway
  • Can work in two Modes
    • Tunnel mode
    • Transport mode

Dr. Peng Ning

hosts gateways
Hosts & Gateways
  • Hosts can implement IPsec to connect to:
    • Other hosts in transport or tunnel mode
    • Or Gateways in tunnel mode
  • Gateways to gateways
    • Tunnel mode

Dr. Peng Ning

tunnel mode

New IP Header

AH or ESP Header

Orig IP Header

TCP

Data

Tunnel Mode

Encrypted Tunnel

Gateway

Gateway

Encrypted

Unencrypted

Unencrypted

A

B

Dr. Peng Ning

tunnel mode cont d
Tunnel Mode (Cont’d)
  • ESP applies only to the tunneled packet
  • AH can be applied to portions of the outer header

Outer IP

header

IPsec

header

Inner IP

header

Higher

layer protocol

ESP

Real IP destination

Destination

IPsec

entity

AH

Dr. Peng Ning

transport mode

New IP Header

AH or ESP Header

TCP

Data

Transport Mode

Encrypted/Authenticated

A

B

Dr. Peng Ning

transport mode cont d
Transport Mode (Cont’d)
  • ESP protects higher layer payload only
  • AH can protect IP headers as well as higher layer payload

IP

header

IP

options

IPsec

header

Higher

layer protocol

ESP

Real IP

destination

AH

Dr. Peng Ning

security association sa
Security Association (SA)
  • An association between a sender and a receiver
    • Consists of a set of security related parameters
    • E.g., sequence number, encryption key
  • One way relationship
  • Determine IPsec processing for senders
  • Determine IPsec decoding for destination
  • SAs are not fixed! Generated and customized per traffic flows

Dr. Peng Ning

security parameters index spi
Security Parameters Index (SPI)
  • A bit string assigned to an SA.
  • Carried in AH and ESP headers to enable the receiving system to select the SA under which the packet will be processed.
  • 32 bits
  • SPI + Dest IP address + IPsec Protocol
    • Uniquely identifies each SA in SA Database (SAD)

Dr. Peng Ning

sa database sad
SA Database (SAD)
  • Holds parameters for each SA
    • Sequence number counter
    • Lifetime of this SA
    • AH and ESP information
    • Tunnel or transport mode
  • Every host or gateway participating in IPsec has their own SA database

Dr. Peng Ning

sa bundle
SA Bundle
  • More than 1 SA can apply to a packet
  • Example: ESP does not authenticate new IP header. How to authenticate?
    • Use SA to apply ESP w/out authentication to original packet
    • Use 2nd SA to apply AH

Dr. Peng Ning

security policy database spd
Security Policy Database (SPD)
  • Decide
    • What traffic to protect?
    • Has incoming traffic been properly secured?
  • Policy entries define which SA or SA Bundles to use on IP traffic
  • Each host or gateway has their own SPD
  • Index into SPD by Selector fields
    • Selectors: IP and upper-layer protocol field values.
    • Examples: Dest IP, Source IP, Transport Protocol, IPSec Protocol, Source & Dest Ports, …

Dr. Peng Ning

spd entry actions
SPD Entry Actions
  • Discard
    • Do not let in or out
  • Bypass
    • Outbound: do not apply IPSec
    • Inbound: do not expect IPSec
  • Protect – will point to an SA or SA bundle
    • Outbound: apply security
    • Inbound: security must have been applied

Dr. Peng Ning

spd protect action
SPD Protect Action
  • If the SA does not exist…
    • Outbound processing
      • Trigger key management protocols to generate SA dynamically, or
      • Request manual specification, or
      • Other methods
    • Inbound processing
      • Drop packet

Dr. Peng Ning

outbound processing

SPD(Policy)

SA Database

Outbound Processing

Outbound packet (on A)

A

B

IP Packet

Is it for IPsec?If so, which policy

entry to select?

IPSec processing

SPI & IPsec Packet

Determine the SA and its SPI

Send to B

Dr. Peng Ning

inbound processing

SPD(Policy)

SA Database

Inbound Processing

Inbound packet (on B)

A

B

From A

SPI & Packet

Use SPI to

index the SAD

Was packet properly

secured?

Original IP Packet

“un-process”

Dr. Peng Ning

authentication header ah
Authentication Header (AH)
  • Data integrity
    • Entire packet has not been tampered with
  • Authentication
    • Can “trust” IP address source
    • Use MAC to authenticate
  • Anti-replay feature
  • Integrity check value

Dr. Peng Ning

integrity check value icv
Integrity Check Value - ICV
  • Message authentication code (MAC) calculated over
    • IP header fields that do not change or are predictable
    • IP header fields that are unpredictable are set to zero.
    • IPsec AH header with the ICV field set to zero.
    • Upper-level data
  • Code may be truncated to first 96 bits

Dr. Peng Ning

ipsec authentication header

SAD

IPsec Authentication Header

Payload Length

6-2=4

Next Header (TCP/UDP)

Reserved

SPI

Sequence Number

ICV

Dr. Peng Ning

encapsulated security protocol esp
Encapsulated Security Protocol (ESP)
  • Confidentiality for upper layer protocol
  • Partial traffic flow confidentiality (Tunnel mode only)
  • Data origin authentication and connectionless integrity (optional)

Dr. Peng Ning

outbound packet processing
Outbound Packet Processing
  • Form ESP payload
  • Pad as necessary
  • Encrypt result [payload, padding, pad length, next header]
  • Apply authentication

Dr. Peng Ning

outbound packet processing1
Outbound Packet Processing...
  • Sequence number generation
    • Increment then use
    • With anti-replay enabled, check for rollover and send only if no rollover
    • With anti-replay disabled, still needs to increment and use but no rollover checking
  • ICV calculation
    • ICV includes whole ESP packet except for authentication data field.
    • Implicit padding of ‘0’s between next header and authentication data is used to satisfy block size requirement for ICV algorithm
    • Not include the IP header.

Dr. Peng Ning

esp transport example
ESP Transport Example

Original IP Header

SPI

Sequence Number

Authentication coverage

Payload (TCP Header and Data)

Variable Length

Encrypted

Padding (0-255 bytes)

Pad

Length

Next

Header

Integrity Check Value

Dr. Peng Ning

inbound packet processing
Inbound Packet Processing
  • Sequence number checking
    • Anti-replay is used only if authentication is selected
    • Sequence number should be the first ESP check on a packet upon looking up an SA
    • Duplicates are rejected!

Check bitmap, verify if new

verify

reject

Sliding Window

size >= 32

0

Dr. Peng Ning

anti replay feature
Anti-replay Feature
  • Optional
  • Information to enforce held in SA entry
  • Sequence number counter - 32 bit for outgoing IPsec packets
  • Anti-replay window
    • 32-bit
    • Bit-map for detecting replayed packets

Dr. Peng Ning

anti replay sliding window
Anti-replay Sliding Window
  • Window should not be advanced until the packet has been authenticated
  • Without authentication, malicious packets with large sequence numbers can advance window unnecessarily
    • Valid packets would be dropped!

Dr. Peng Ning

inbound packet processing1
Inbound Packet Processing...
  • Packet decryption
    • Decrypt quantity [ESP payload,padding,pad length,next header] per SA specification
    • Processing (stripping) padding per encryption algorithm; In case of default padding scheme, the padding field SHOULD be inspected
    • Reconstruct the original IP datagram
  • Authentication verification (option)

Dr. Peng Ning

esp processing header location
ESP Processing - Header Location...
  • Transport mode IPv4 and IPv6

IPv4

Orig

IP hdr

ESP

hdr

TCP

Data

ESP

trailer

ESP

Auth

IPv6

Orig

IP hdr

Orig

ext hdr

ESP

hdr

TCP

Data

ESP

trailer

ESP

Auth

Dr. Peng Ning

esp processing header location1
ESP Processing - Header Location...
  • Tunnel mode IPv4 and IPv6

IPv4

New

IP hdr

ESP

hdr

Orig

IP hdr

TCP

Data

ESP

trailer

ESP

Auth

IPv6

New

IP hdr

New

ext hdr

ESP

hdr

Orig

IP hdr

Orig

ext hdr

TCP

Data

ESP

trailer

ESP

Auth

Dr. Peng Ning