IPsec
Shu Zhang
IPsec
Definition: (Webopedia)
Short for IP Security, a set of protocols
developed by the IETF to support secure
exchange of packets at the IP layer. IPsec
has been deployed widely to implement
Virtual Private Networks (VPNs)
Virtual Private Network (VPN)
More and more across-country or
worldwide companies due to global
market
there is a problem for all of them
how to maintain fast, secure and reliable
communications wherever their offices are
Leased lines
very expensive
Virtual Private Network (VPN)
VPN: using public wires, usually
Internet to connect company’s private
network, remote sites and users
together, instead of using a dedicate,
real-world connection.
Virtual Private Network (VPN)
Features of VPN:
Security
Reliability
Scalability
Network management
Policy management
VPN Security
Several Methods:
Firewall
Encryption
IPsec
AAA server
Goal of IPsec
Provides security services at IP layer
Access control
Integrity
Data origin Authentication
Rejection of replayed packets
Confidentiality
IPsec Architecture
Components
Security Protocols
Security Associations
Key Management
Algorithms for authentication and
encryption
Security Protocols
Authentication Header (AH)
Data Origin Authentication
Anti-replay service
Data Integrity
Encapsulating Security Payload (ESP)
Confidentiality
Data Origin Authentication
Anti-replay service
Connectionless Integrity
AH
AH provides authentication for as much
of the IP header as possible, as well as
for upper level protocol data
Tow modes: transport mode/tunnel
mode
AH Location
AH Algorithms
Keyed Message Authentication Codes
(MAC) based on Symmetric Key
Encryption( DES)
One-way hash function (MD5/SHA-1)
ESP
Provides Data Confidentiality to IP
payload using Encryption
It can provides Data Integrity and
connectionless Integrity, but the
coverage is different from AH
Two: transport Mode/Tunnel Mode
ESP Format
ESP Algorithms
Encryption Algorithms
Symmetric Encryption Algorithms
Authentication Algorithms
The same as AH
Security Associations (SA)
A management Component used to enforce a
security policy in the IPsec environment
A simplex “connection” that affords security
services to the traffic it carries
The set of security services depends on:
Protocol selected
SA mode
Endpoints of the SA
SA’s Mode
Transport Mode
Between 2 hosts
Transport Mode AH
The protection is to selected portions of IP
header and higher layer protocol header
Transport Mode ESP
The protection is only for the higher layer
SA’s Mode
Tunnel Mode
Applied to an IP tunnel
Tunnel Mode AH
Portions of “outer” IP header, as well as all of
“inner” IP packet
Tunnel Mode ESP
Only to the tunneled packet
DataBases in IPsec
Two databases are maintained in each
IPsec implementation:
Security Policy Database (SPD)
Security Association Database (SAD)
SPD
Contains an ordered list of policy entries
keyed by selectors
Destination/Source IP Address
Transport Layer protocol
Destination/Source Port
Each entry includes:
SA specification
IPsec protocol
Modes
algorithms
SPD
An administrative interface must be
provided to user or system
administrator
Must be consulted during the all the
traffic processing, including non-IPsec
traffic
SAD
Each entry defines the parameters associated
with one SA
Sequence Number Counter
Anti_replay window
AH Authentication algorithm, keys
ESP Encryption algorithm, keys
ESP Authentication algorithm, keys
Lifetime of SA
IPsec Protocol Mode
IPsec Processing
Differentiate inbound/outbound traffic
For outbound
Entries are pointed to by entries in SPD
If not, create a new SA
For inbound
A triple is used to uniquely identify a SA
Security Parameter Index
32-bit value
Selected by destination system when a
new SA is established
SA Management Protocol
Internet Security Association and Key
Management Protocol (ISAKMP) is the
framework for SA management
It defines:
Procedure and Packet format to establish,
negotiate, modify and delete SAs
Payloads for exchanging key generation
and authentication data
ISAKMP
ISAKMP has 3 main functions
Security Associations and Management
Negotiation:
authentication mechanism
cryptographic algorithm
algorithm mode
key length
nitialization Vector (IV)
……
Establishment
ISAKMP
Authentication
Authenticate the entity at the other end of
Communication
Strong Authentication must be provided
Digital signature
Public Key Encryption
obtain shared secrets and session keys
Key Establishment: Key generation/Key
transport
Key Exchange Authentication
ISAKMP Negotiation
Offer 2-phase negotiation
Phase 1: establish an ISAKMP SA to protect
further negotiation
Phase 2: establish real protocol SAs
Higher start-up cost
Benefit:
Multiple Protocol SAs can be established
Allow to use simpler second phase exchanges
ISAKMP SA reduces ISAKMP management
activities
ISAKMP Protection
Denial-of-service
A anti-clogging token (ACT)
Man-in-the-middle attack
Authentication and Encryption
Algorithms
Not bounded to any specific
cryptographic algorithm, key generation
technique, or security mechanism
Supports the dynamic communications
environment
Provides a forward migration path to better
mechanisms and algorithms