1. Sheng-Liang Song ssl@cisco.com
IPSec
Access control
Connectionless integrity
Data origin authentication
Rejection of replayed packets
Confidentiality
Sheng-Liang Song

2. Sheng-Liang Song ssl@cisco.com
IPSec
Complexity
Security worst “enemy”
“best practice”
Sheng-Liang Song

3. Agenda IPSec Overview IPSec Discussion Q&A IPSec (Network Layer)
Modes (Tunnel/Transport)
Protocols (ESP/AH)
IKE (Internet Key Exchange)
IPSec Cases
IPSec Discussion
Q&A

4. Key Words ISAKMP (Internet Security Association
and Key Management Protocol)
SA (Security Associations)
SPD (Security Policy Database)
IKE (Internet Key Exchange)
AH (Authentication Header)
ESP (Encapsulating Security Payload)
HMAC (Keyed-Hashing for Message Authentication)
H(K XOR opad_5C, H(K XOR ipad_36, text))

5. IPSec (Network Layer) lives at the network layer
transparent to applications
application
transport
network
link
physical
User
SSL OS
IPSec
NIC

6. IPv4 Header Format
Mutable, predictable, Immutable

7. IPv6 Header Format

8. IPSec Modes (Tunnel and Transport)
Transport Mode
Tunnel Mode
Transport Mode
IP header
data
IP header
ESP/AH
data
Tunnel Mode
IP header
data
new IP hdr
ESP/AH
IP header
data

9. IPSec Protocols (ESP and AH)
ESP (Encapsulating Security Payload)
Integrity and confidentiality (HMAC/DES-CBC)
Integrity only by using NULL encryption
AH (Authentication Header)
Integrity only
IP HDR
Data
IPSec Tunnel
Original IP Layer
encrypted
IPSec Encrypted session
IPSec Authenticated session
AH HDR
ESP HDR
New IP HDR

10. AH Format
The sender's counter is initialized to 0 when an SA is established.

11. AH/Transport

12. AH/Transport

13. ESP Format
The sender's counter is initialized to 0 when an SA is established.

14. ESP/Transport

15. ESP/Tunnel

16. IPSec Tunnels Original IP Packet Classified IP packet IPSec packet
IP header
TOS
IP Payload
IP header
IP Payload
Classified IP packet
Set TOS
TOS
Original IP Packet
TOS copy
TOS
IP new hdr
New IP header built by tunnel entry point
TOS byte is copied
IP new hdr
ESP header
IPSec packet IP
IP Payload
TOS

17. Anti-Replay in IPSec Both ESP and AH have an anti-reply mechanism
based on sequence numbers
sender increment the sequence number after each transmission
receiver optionally checks the sequence number and rejects if it is out of window

18. How IPSec uses IKE

19. IPSec and IKE in Practice
Sets up a keying channel
Sets up data channels
Internal Network
Certificate Authority
Digital Certificate
ISAKMP Session
Digital Certificate SA
Authenticated Encrypted Tunnel
ISAKMP (Internet Security Association
and Key Management Protocol)
SA (Security Associations)
SPD (Security Policy Database)
Discard,bypass IPsec, apply IPSec
(Overhead)
Clear Text
Internal Network
Encrypted

20. IPSec (IKE1 Phase1) Authenticated with Signatures
Authenticated with Shared key
Authenticated with Public Key Encryption
Authenticated with Public Key Encryption (Revised)

21. IPSec (Cases)

22. IPSec Case1

23. IPSec Case2

24. IPSec Case3

25. IPSec Case4

26. Q & A IPSec Discussion IPSec authenticates machines, not users
Does not stop denial of service attacks
Easier to do DoS
Order of operations: Encryption/Authentication
Q & A
L2,L3,L4 Parsing
Header(IP,TCP,UDP) checking
Packet action classifying
Probabilistic content matching

27. Reference
Information Security: Principles and Practice, Mark Stamp, Jan 29,2005
Cisco IOS IPsec
Cisco White Paper, IPsec,
N. Ferguson and B. Schneier, A Cryptographic Evaluation of IPsec,
IPsec, Security for the Internet Protocol,