IP SECURITY

1. IP SECURITY

2. IPSec Three Functional Areas • IPSec encompasses three functions, • Authentication • Identify the Source address, i.e., against the forgers. • Against alteration (Plaintext transmit only) • Confidentiality • Prevent eavesdropping by 3rd party (ciphertext transmit) • Key management • Exchange the secret keys securely.

3. IPSec Overview • Flexibility • Not a sigle protocol • (Security algorithms decided by the pair of comm. entites) + (General framework) • Transparent to applications • Encrypt and/or all traffic at the IP level. • All the distributed applications could be secured.

4. Applications • Secure branch office connectivity over the Internet • Secure remote access over the Internet • Establsihing extranet and intranet connectivity with partners • Enhancing electronic commerce security

5. Individual user is available Encrypt and compress IPSec Scenario

6. RFC-2401 RFC-2406 RFC-2402 RFC-2403,4 HMAC-SHA-1 HMAC-MD5 RFC-2403~5 3DES-CBC CAST Domain of Interpretation IPSec Document Overview

7. Security Association (SA) • A one-way relationsship between a sender and a receiver that specifies the parameters to the traffic carried. • Who to protect the traffic, what traffic to be protected and with whom the protection is performed. • Typically, SAs exist in pairs, one in each direction. • SAs reside in the Security Association Database.

8. Identified by three parameters: • Security Parameter Index (SPI) • Bit string assigned to the certain SA, local sinificant only. • Carried in AH or ESP heades • IP Destination address • Unicast addresses only • Security Protocol Identifier • Indicate whether it’s a AH or ESP.

9. Security Association Database (SAD) • Defines the parameters associated within each SA. • The functionality provided by a SAD must be present in IPSec, however, the way it presents is depends on the implementor.

10. SA 8-Parameter in SAD • Sequence Number Counter • 32-bit value • Use to generate the sequence number in AH or ESP header • Sequence Counter overflow • If overflow, generate an auditable event and terminate such a SA. • Anti-Replay Window • Determine whether an inbound AH or ESP packet is replay.

11. AH Information • All the details of authentication algorithm within this SA. • ESP Information • All the details of the Encryption algorithm within this SA. • Lifetime of this Security Association • IPSec protocol Mode • Tunnel, Transport, or wildcard. • Path MTU

12. Anti-Replay Mechanism • Sequence number (Sender) • 1. The sender initialized a sequence number counter once a new SA is established. • 2. The sender will increase the sequence number by one once a packet is sent on this SA till the limit, (232 – 1), is reached. • 3. The sender should terminate a SA in which the sequence number is maximum and negotiate a new SA with a new key.

13. Advance the window if the valid packet to the “right” is received irretrievably lost Fixed window size Unmarked if valid packet not yet received • Sliding receive window (Receiver)

14. Security Policy Database (SPD) • Maintain the IPSec policies. • Each entry defines, • Which IP traffic to be protected, • IP traffic  selectors IPSec policy. (SPD) • How to protect it. One of three actions to take upon IP traffic match • Discard • Bypass • Apply  An SA or a bundle of SAs. • With whom the protection is shared

15. Map to the SAD. (per packet or per SPD entry). In other words, points to an SA for a certain IP traffic.

16. SA 10-Selector in SPD • Destination IP address • Source IP address • UserID • Data Sensitivity level • Transport layer protocol • IPSec protocol • Source and Destination ports • IPv6 class • IPv6 Flow label • IPv4 Type of Service(TOS)

17. IPSec • SA • AH or ESP or ESP/AH • AH • Authenticated only, i.e., the payload of the IP packet will be transmitted in “plaintext”. • ESP • Authentication is an option. • Ciphertext • Each AH and ESP has two modes • Transport • Tunnel

18. Transport Mode vs. Tunnel Mode • Transport mode • Only the IP payload will be protected. • Origin IP address is the outbound address. • Tunnel mode • The entire IP packet (including IP address) will be protected. • A router or firewall’s IP address will be the destination address instead.

19. Authentication Header (AH) • Design to provide • Integrity • Authentication • Does not support • Confidentiality • Guards against the replay attack

20. AH Fields • Next header: • Identify the type of the next header. • IP protocol number for AH is 51. • Payload length: • {[Total length of AH (in word) ] – 2 } • In default case, the length is 4. • Reserved • For future usage. • SPI: • Identifies a SA • Sequence number: • a monotonically increasing counter for anti-replay.

21. Authentication data: • contains Integrity check value (ICV) or message authentication code (MAC) • HMAC-MD5-96 • HMAC-SHA-1-96

22. MAC Calculation • IP header • immutable : available • mutable but predictable : available • mutable but unpredictable : set to zero • TOS, Flags, TTL, IP hdr checksum, fragment offset • AH header • Other than the Authentication Data field. • Namely, set that field to zero. • IP payload • immutabel.

23. 0 4 8 16 19 31 Ver IHL TOS Total length Identification Flag Fragment Offset TTL Protocol HeaderChecksum Source Address Destination Address Options + Padding Mutable Field in IPv4 Format

24. Mutable Fields in IPv6 Format 0 4 8 16 19 31 Ver TrafficClass Flow Label Payload length Next hdr Hoplimit 4-word 4-word Source Address DestinationAddress Extension Header

25. IPv6 Header Hop-by-Hop opt. hdr Destination Opt. hdr Routing Header Fragment Header AH ESP Destination Opt. hdr IPv6 with Extension Headers

26. 0 8 16 31 Next Header Payload Length Reserved Security Parameters Index (SPI) Sequence Number Authentication Data (variable) AH Format

27. Orig IP hdr TCP Data IPv4 Orig IP hdr Extension headers (If present) TCP Data IPv6 Origin IPv4 and IPv6

28. Authenticated except for mutable fields Authenticated except for mutable fields Orig IP hdr AH TCP Data IPv4 Orig IP hdr Hop-by-hop, dest, routing, fragment AH dest TCP Data IPv6 Transport Mode AH

29. Authenticated except for mutable fields in the new IP hdr Authenticated except for mutable fields in the new IP hdr and its extension hdrs New IP hdr AH IP Orig IP hdr TCP TCP Data Data IPv4 IPv4 New IP hdr Extension headers AH Orig IP hdr Extension headers TCP Data IPv6 Tunnel Mode AH

30. AH Approach Transport SA Transport SA Tunnel SA

31. Encapsulating Security Payload (ESP) • ESP • Provide confidentiality only. • ESP/AH • Support both encryption and authentication

32. ESP Fields • Security parameters index (SPI) • Identifies a certain SA • Sequence number • The same as in AH • Payload data • protected by encryption • Padding • Encryption algorithm • Next header • Identifies the type of data contained in the payload. • IP protocol number is 50. • Authentication data • MAC computes over the (ESP packet – Authentication Data)

33. 0 16 24 31 Security Parameters Index (SPI) Authentication coverage Confidentiality coverage Sequence Number Payload Data (variable) Padding (0-255 bytes) Pad Length Next Header Authentication Data (variable) ESP Format

34. Encryption and Authentication in ESP • Encryption algorithm • The cryptographic synchronization (IV) may be carried at the beginning of the payload • Although being part of the ciphertext, IV won’t, in general, be encrypted. • Essential : DES in CBC mode • Others : 3DES, RC5, IDEA, 3IDEA, CAST, Blowfish symmetric key encryption • Authentication algorithm • The same as in AH. • Ciphertext+ ESP tailer

35. Authenticated Encrypted Orig IP hdr ESP hdr TCP Data ESP trlr ESP auth IP TCP Data IPv4 IPv4 Authenticated Encrypted Orig IP hdr Hop-by-hop, dest, routing, fragment ESP hdr dest TCP Data ESP trlr ESP auth IPv6 Transport Mode ESP

36. Authenticated Encrypted new IP hdr ESP hdr Orig IP hdr TCP Data ESP trlr ESP auth IPv4 IP TCP Data IPv4 Authenticated Encrypted new IP hdr ext headers ESP hdr orig IP hdr ext headers TCP Data ESP trlr ESP auth IPv6 Tunnel Mode ESP

37. Transport-level security VPN via Tunnel Mode ESP Approach

38. Functionality of Tunnel and Transport Mode

39. IPSec Services Summary