1. IP Security Ch16 of Cryptography and Network Security - Third Edition
by William Stallings
Modified from lecture slides by Lawrie Brown
CIM3681: NSP 03 - IP Security

2. IP Security
If a secret piece of news is divulged 泄露,暴露 by a spy before the time is ripe 成熟的 , he must be put to death, together with the man to whom the secret was told.
—The Art of War, Sun Tzu
CIM3681: NSP 03 - IP Security

3. IP Security IPSec IP Security Architecture 組織,結構
Authentication Header 鑑別表頭
Encapsulating 封進內部 Security Payload 有效負荷
Combining Security Associations
Key Management
CIM3681: NSP 03 - IP Security

4. IP Security
have considered some application specific security mechanisms
eg. S/MIME, PGP, Kerberos, SSL/HTTPS
however there are security concerns that cut across 橫跨 protocol layers
would like security implemented by the network for all applications
CIM3681: NSP 03 - IP Security

5. IPSec general IP Security mechanisms provides
authentication
confidentiality
key management
applicable to use over LANs, across public & private WANs, & for the Internet
CIM3681: NSP 03 - IP Security

6. IPSec Uses
Stallings Fig 16-1.
CIM3681: NSP 03 - IP Security

7. Benefits of IPSec
in a firewall/router provides strong security to all traffic crossing the perimeter 周界
is resistant to bypass 繞過
is below transport layer, hence transparent 透明 to applications
can be transparent to end users
can provide security for individual users if desired 需求
CIM3681: NSP 03 - IP Security

8. IP Security Architecture
specification 規格 is quite complex
defined in numerous RFC’s
incl. RFC 2401/2402/2406/2408
many others, grouped by category
mandatory 強制 in IPv6, optional in IPv4
CIM3681: NSP 03 - IP Security

9. IPSec Document Overview
CIM3681: NSP 03 - IP Security

10. IPSec Services Access control 存取控制 Connectionless integrity 無連接方式完整性
Data origin authentication 數據起源鑑別
Rejection of replayed 重演 packets
a form of partial sequence integrity
Confidentiality (encryption)
Limited traffic flow confidentiality
CIM3681: NSP 03 - IP Security

11. IPSec Services
CIM3681: NSP 03 - IP Security

12. Security Associations
a one-way relationship between sender & receiver that affords 負擔得起 security for traffic flow
defined by 3 parameters: 參數
Security Parameters Index (SPI)
IP Destination Address
Security Protocol Identifier
has a number of other parameters
seq no, AH & EH info, lifetime etc
have a database of Security Associations
CIM3681: NSP 03 - IP Security

13. Authentication Header (AH) 鑑別表頭
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
CIM3681: NSP 03 - IP Security

14. Authentication Header
Stallings Fig 16-3.
CIM3681: NSP 03 - IP Security

15. Transport & Tunnel Modes
Stallings Fig 16-5.
CIM3681: NSP 03 - IP Security

16. Tunnel Mode and Transport Mode Functionality
CIM3681: NSP 03 - IP Security

17. 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
CIM3681: NSP 03 - IP Security

18. Encapsulating Security Payload
Stallings Fig 16-7.
CIM3681: NSP 03 - IP Security

19. Transport 傳送 vs Tunnel 隧道 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
CIM3681: NSP 03 - IP Security

20. Combining Security Associations
SA’s can implement either AH or ESP
to implement both need to combine SA’s
form a security bundle
have 4 cases (see next)
CIM3681: NSP 03 - IP Security

21. Combining Security Associations
Stallings Fig
CIM3681: NSP 03 - IP Security

22. 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
CIM3681: NSP 03 - IP Security

23. Oakley a key exchange protocol based on Diffie-Hellman key exchange
adds features to address weaknesses
cookies, groups (global params), nonces, DH key exchange with authentication
can use arithmetic in prime fields or elliptic curve fields
CIM3681: NSP 03 - IP Security

24. ISAKMP Internet Security Association and Key Management Protocol
provides framework for key management
defines procedures and packet formats to establish, negotiate, modify, & delete SAs
independent of key exchange protocol, encryption alg, & authentication method
CIM3681: NSP 03 - IP Security

25. ISAKMP
Stallings Fig
CIM3681: NSP 03 - IP Security

26. Summary have considered: IPSec security framework AH ESP
key management & Oakley/ISAKMP
CIM3681: NSP 03 - IP Security