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IPSec_IP Authentication Header
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IPSec_IP Authentication Header

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IPSec_IP Authentication Header

IPSec_IP Authentication Header

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Transcript

  • 1. IP Authentication Header righthand 2013-11-29 1
  • 2. Introduction • IPSec is a collection of protocols that assist in protecting communications over IP networks. • The IP Authentication Header (AH) offers integrity and data origin authentication, with optional anti-replay features. 2
  • 3. Authentication Header Format 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 Next Header the length of Authentication Header in 4-byte units minus 2 7 8 9 0 Payload Length the type of next payload after the Authentication Header 6 1 2 3 4 5 6 7 8 9 0 Reserved reserve for future use Security Parameters Index (SPI) determine which Security Association (SA) is being used Sequence Number Field counter value to against replay attacks Integrity Check Value (ICV) variable-length that contains Integrity Check Value (MAC Output) for this packet 3 1
  • 4. Authentication Header Location • Transport Mode IP Header AH Header ← mutable field processing →← ← Transport and Application Protocol Headers and Data → → immutable field Authenticated (Integrity Protection) • Tunnel Mode New IP Header AH Header ← mutable field processing →← ← Original IP Header Transport and Application Protocol Headers and Data → → immutable field Authenticated (Integrity Protection) – Mutable • Time To Live (TTL) • IP Header Checksum 4
  • 5. Integrity Algorithm and Protection • Message Authentication Code – HMAC-MD5-96, HMAC-SHA-1-96 • "what do ya want for nothing?" + "Jefe" = 0x750c783e6ab0b503eaa86e310a5db738 • "what do ya want for nothing" + "Jefe" = 0xfa9a09b5ba15e378e076da81acaa2078 – AES-XCBC-MAC-96 5
  • 6. Processing • Outbound Packet – Security Association (SA) Lookup – Sequence Number Generation – Integrity Check Value Calculation – Fragmentation IP Packet SPD … SAD • Inbound Packet – Security Association (SA) Lookup – Sequence Number Verification – Integrity Check Value Verification – Reassembly … SPI IPSec Packet 6
  • 7. Example 7
  • 8. References • RFC 4302 - IP Authentication Header • NIST SP 800-77 Guide to IPSec VPNs 8