1. IP Security: Security Across the Protocol Stack

2. IP Security There are some application specific security mechanisms
eg. S/MIME, PGP, Kerberos, SSL/HTTPS
however there are security concerns that cut across protocol layers
would like security implemented by the network for all applications

3. What is IPSec?
A collection of tools and algorithms (protocols) for securing network connections
The protocol is designed so as to provide network level security for IPv4 and IPv6 datagrams
General IP security mechanisms
applicable to use over LANs, across public & private WANs, & for the Internet
It provides - authentication
confidentiality
key management

4. Services Provided by IPsec
Authentication – ensure the identity of an entity
Confidentiality – protection of data from unauthorized disclosure
Key Management – generation, exchange, storage, safeguarding, etc. of keys in a public key cryptosystem

5. Benefits of IPSec
If implemented in a firewall/router it provides strong security to all traffic crossing the perimeter
IPSec in firewall is resistant to bypass
IPSec is below transport layer, hence transparent to applications. No need to change software on a user or server system
IPSec can be transparent to end users
IPSec can provide security for individual users if desired

6. IPSec Scenario
Stallings Fig 16-1.

7. IP Security Architecture
specification is quite complex
defined in numerous RFC’s
incl. RFC 2401/2402/2406/2408
many others, grouped by category
mandatory in IPv6, optional in IPv4

8. Where can IPSec be used These protocols can operate in
networking devices,
such as a router or firewall
or they may operate directly on the workstation or server.

9. How can IPSec be used Secure Communications between devices
Workstation to Workstation
Protection against data changes
Accidental or Intentional
Contents can be hidden
Secure communicatoins through IPSec tunnels

10. IPSec
IPSec provides security services at IP layer by three main facilities
An authentication-only function,
Referred to as Authentication Header (AH)
A combined authentication/ encryption function
Called Encapsulating Security Payload (ESP)
A key exchange function.
Internet key exchange IKE (ISAKMP / Oakley)

11. IPSec Services Access control Connectionless integrity
Data origin authentication
Rejection of replayed packets
a form of partial sequence integrity
Confidentiality (encryption)
Limited traffic flow confidentiality

12. Security Associations
a one-way relationship between sender & receiver that affords security services to the traffic carried on it
A SA is an agreement between two communicating hosts on the IPSEC protocol used (i.e. AH/ESP), cryptographic algorithm used, mode of operation of protocols, cryptographic keys and lifetime of the keys
Uniquely identified by 3 parameters:
Security Parameters Index (SPI)
IP Destination Address
Security Protocol Identifier

13. Security Associations
have a database of Security Associations
Security Associations Database (SAD)
has a number of other parameters
seq no, AH & EH info, lifetime etc.
If a peer relationship is needed, for two-way secure exchange, then two security associations are required
The SA is negotiated between peers using a Key Management Protocol namely Internet Key Exchange Protocol (IKE).
The peers maintain a SA database (SAD) with a list of all active SA entries.

14. Security Associations (SA)
Security Parameters Index (SPI)
The SPI is a bit string assigned to the SA that has local significance only.
The SPI is carried in AH and ESP headers to enable the receiving system to select the SA under which a received packet will be processed.

15. Security Associations (SA)
IP destination address
The IP address of the destination endpoint of the SA
May be an end-user system
Or, a network system such as a firewall or router.
Currently, only unicast addresses are allowed

16. Security Associations (SA)
Security Protocol Identifier
Indicates which IPSec protocol is in use on the SA
AH (Authentication only)
ESP (complete encryption and possibly Authentication)

17. Transport vs. Tunnel Mode
The transport mode is the default mode for IPSEC.
In transport mode only the IP payload is encrypted or authenticatedProtection for upper layers-TCP,UDP,ICMP)
whereas in tunnel mode IPSEC encrypts(or hashes) the IP header with the payload.
Transport mode can be used to encrypt traffic between end-to-end clients (client-server, 2 workstations)
whereas tunnel mode would be used to encrypt traffic between gateways connecting different networks

18. Authentication Header (AH)
provides support for data integrity & authentication of IP packets
end system/router can authenticate user/app
prevents address spoofing attacks by tracking sequence numbers
based on use of a MAC
HMAC-MD5-96 or HMAC-SHA-1-96
parties must share a secret key

19. Authentication Header
Stallings Fig 16-3.

20. Next Header (8 bits)  Type of the next header, indicating what upper-layer protocol was protected. The value is taken from the list of IP protocol numbers.
Payload Len (8 bits)  The length of this Authentication Header in 4-octet units, minus 2 (a value of 0 means 8 octets, 1 means 12 octets, etc.). Although the size is measured in 4-octet units, the length of this header needs to be a multiple of 8 octets if carried in an IPv6 packet. This restriction does not apply to an Authentication Header carried in an IPv4 packet.
Reserved (16 bits)  Reserved for future use (all zeroes until then).
Security Parameters Index (32 bits)  Arbitrary value which is used (together with the source IP address) to identify the security association of the sending party.
Sequence Number (32 bits)  A monotonically increasing sequence number (incremented by 1 for every packet sent) to prevent replay attacks.
Integrity Check Value (multiple of 32 bits)  Variable length check value. It may contain padding to align the field to an 8-octet boundary for IPv6, or a 4-octet boundary for IPv4

22. IPSec Authentication Header (AH) in Transport Mode
Orig IP Hdr
TCP Hdr
Data
Insert
Orig IP Hdr
AH Hdr
TCP Hdr
Data
Integrity hash coverage (except for mutable fields in IP hdr)
Next Hdr
Payload Len
Rsrv
SecParamIndex
Seq#
Keyed Hash
AH is IP protocol 51
24 bytes total
© 2000 Microsoft Corporation

24. © 2000 Microsoft Corporation
IPSec AH Tunnel Mode
Data
TCP Hdr
Orig IP Hdr
IP Hdr
AH Hdr
Data
TCP Hdr
Orig IP Hdr
Integrity hash coverage (except for mutable new IP hdr fields)
New IP header with source & destination IP address
© 2000 Microsoft Corporation

27. Transport & Tunnel Modes
Stallings Fig 16-5.

28. Encapsulating Security Payload (ESP)
Must encrypt and/or authenticate in each packet
ESP a bit more complicated because the encapsulation surrounds the payload rather than precedes it as with AH: ESP includes header and trailer fields to support the encryption and optional authentication
Encryption occurs before authentication
Authentication is applied to data in the IPSec header as well as the data contained as payload

29. Encapsulating Security Payload (ESP)
provides message content confidentiality & limited traffic flow confidentiality
can optionally provide the same authentication services as AH
supports range of ciphers, modes, padding
incl. DES, Triple-DES, RC5, IDEA, CAST etc
CBC most common
pad to meet blocksize, for traffic flow

30. Encapsulating Security Payload
Stallings Fig 16-7.

31. IPSec Encapsulating Security Payload (ESP) in Transport Mode
Orig IP Hdr
TCP Hdr
Data
Insert
Append
Orig IP Hdr
ESP Hdr
TCP Hdr
Data
ESP Trailer
ESP Auth
Usually encrypted
integrity hash coverage
SecParamIndex
Seq#
InitVector
Keyed Hash
Padding
PadLength
NextHdr
22-36 bytes total
ESP is IP protocol 50
© 2000 Microsoft Corporation

33. © 2000 Microsoft Corporation
IPSec ESP Tunnel Mode
Data
TCP Hdr
Orig IP Hdr
Data
TCP Hdr
ESP Hdr
IP Hdr
IPHdr
ESP Trailer
ESP Auth
Usually encrypted
integrity hash coverage
New IP header with source & destination IP address
© 2000 Microsoft Corporation

35. Transport vs Tunnel Mode ESP
transport mode is used to encrypt & optionally authenticate IP data
data protected but header left in clear
can do traffic analysis but is efficient
good for ESP host to host traffic
tunnel mode encrypts entire IP packet
add new header for next hop
good for VPNs, gateway to gateway security

36. Key Management handles key generation & distribution
typically need 2 pairs of keys
2 per direction for AH & ESP
manual key management
sysadmin manually configures every system
automated key management
automated system for on demand creation of keys for SA’s in large systems
has Oakley & ISAKMP elements