THE USE OF IP ESP TO PROVIDE A MIX OF SECURITY SERVICES IN IP DATAGRAM

1
THE USE OF IP ESP TO PROVIDE A MIX OF SECURITY
SERVICES IN IP DATAGRAM

• SREEJITH SREEDHARAN
• CS843 PROJECT PRESENTATION
• 04/28/03

2
INTRODUCTION

• ESP can be used to provide
• confidentiality
• data origin authentication
• connectionless integrity
• there are three possible ESP security
  service combinations involving these services
  - confidentiality-only
• -     integrity-only
• -     confidentiality and integrity
• anti-replay service
• traffic flow confidentiality.

3
ESP PACKET FORMAT

• A diagram of a secure IP datagram.
• lt-- Unencrypted
  --gtlt---- Encrypted ------gt
• -----------------------------------------
  -------------------------------
• IP Header Other IP Headers ESP
  Header encrypted data
• -----------------------------------------
  ------------------------------- 

4
ESP PACKET FORMAT

• The figure illustrates the top-level format of an
  ESP packet
•   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  2 3 4 5 6 7 8 9 0 1
• ----------------------
  ----- ----------------
• Security
  Parameters Index (SPI)
  Integrity
• ----------------------
  ----- Coverage
• Sequence
  Number
  
• ----------------------
  ----- ---------------
• Payload Data
  (variable)
  
• 
  
  
• 
  
  Confidentiality
• ----------------
  ------- Coverage
• Padding
  (0-255 bytes)
  
• ----
  --------------
  
• 
  Pad Length Next Header v
  v
• ----------------------
  ----- ------------------
• Integrity Check
  Value-ICV (variable)
• 
  
  
• 
  
  
• ----------------------
  -----

5
ESP PACKET FORMAT

• 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
  4 5 6 7 8 9 0 1
• -----------------------
  ----
• Security
  Parameters Index (SPI)
• -----------------------
  ----
• 
  Sequence Number
• -----------------------
  ---- ------------
• 
  IV (optional
  p
• -----------------------
  ---- a
• Rest of
  Payload Data (variable)
  y
• 
  
  l
• 
  
  o
• ----------------
  ------- a
• TFC Padding
  (optional, variable) v
  d
• ---- ------------
  ------- --------------
• 
  Padding (0-255 bytes)
• --------
  --------------
• Pad Length
  Next Header
• -----------------------
  ----
• Integrity Check
  Value-ICV (variable)

6
ESP ALGORITHMIC MODES

• Encryption Algorithms
• Integrity Algorithms
• Combined Mode Algorithms

7
ESP ALGORITHMIC MODES

• Separate Encryption and Integrity Algorithms
• 
  What What
  What
• 
  of Requ'd Encrypt
  Integ is
• 
  bytes 1 Covers
  Covers Exempted
• 
  ------ ------ ------
  ------ ------
• SPI 4
  M
  Y plain
• Seq (low order bits) 4
  M Y
  plain p
• 
  ------ a
• IV
  variable O Y
  plain y
• IP datagram 2 variable
  M or D Y Y
  cipher3 -- l
• TFC padding 4 variable
  O Y Y
  cipher3 o
• 
  ------ a
• Padding 0-255
  M Y
  Y cipher3 d
• Pad Length 1
  M Y
  Y cipher3
• Next Header 1
  M Y
  Y cipher3
• Seq (high order bits) 4
  Y not xmtd
• ICV Padding variable
  if need Y
  not xmtd
• ICV variable
  M 5 plain

8
ESP ALGORITHMIC MODES

• Combined Mode Algorithms
• 
  What What
  What
• 
  of Requ'd Encrypt
  Integ is
• 
  bytes 1 Covers
  Covers Exempted
• 
  ------ ------ ------
  ------ ------
• SPI 4
  M
  plain
• Seq (low order bits) 4
  M
  plain p
• 
  ------ a
• IV
  variable O Y
  plain y
• IP datagram 2 variable
  M or D Y Y
  cipher -- l
• TFC padding 3 variable
  O Y Y
  cipher o
• 
  ------ a
• Padding 0-255
  M Y
  Y cipher d
• Pad Length 1
  M Y
  Y cipher
• Next Header 1
  M Y
  Y cipher
• Seq (high order bits) 4
  Y 4
• ICV Padding variable
  if need Y
  4
• ICV omitted
  when this mode is employed

9
ESP PROCESSING MODES

• Transport Mode Processing
• Tunnel Mode Processing

10
Transport Mode Processing

• BEFORE APPLYING ESP (IPv4)
• -------------------------------------
  --------------------
• orig IP hdr (any options)
  TCP Data
• -------------------------------------
  -------------------- 
• AFTER APPLYING ESP
• -------------------------------------
  --------------------------------------------------
  ------------
• orig IP hdr (any options) ESP
  Hdr TCP Data ESP Trailer ESP ICV
  
• -------------------------------------
  --------------------------------------------------
  ------------
  
  lt---- encryption ----gt
  lt--------
  integrity -------gt
• BEFORE APPLYING ESP (IPv6)
• ------------------------------------
  -------------------------
• orig IP hdr ext hdrs if
  present TCP Data
• ------------------------------------
  ------------------------- 
• AFTER APPLYING ESP
• ------------------------------------
  --------------------------------------------------
  -----
• orig hop-by-hop,dest,
  dest ESP
  ESP
• IP hdr routing,fragment
  ESP opt TCP Data Trailer ICV
  
• ------------------------------------
  --------------------------------------------------
  -----
  lt--- encryption
  ----gt
  lt------
  integrity ------gt 

11
Tunnel Mode Processing

• BEFORE APPLYING ESP (IPv4)
• -----------------------------------------
  ----------------
• orig IP hdr (any options) TCP
  Data
• -----------------------------------------
  ---------------- 
• AFTER APPLYING ESP
• -----------------------------------------
  ----------------------------------------------
• new IP hdr orig
  IP hdr ESP
  ESP
• (any options) ESP (any
  options) TCP Data Trailer ICV
  
• -----------------------------------------
  ----------------------------------------------
  
  lt--------- encryption
  ---------gt
• lt-------------
  integrity ------------gt 
• BEFORE APPLYING ESP (IPv6)
• -----------------------------------------
  --------------------
• orig IP hdr ext hdrs if present
  TCP Data
• -----------------------------------------
  -------------------- 
• AFTER APPLYING ESP
• ----------------------------------------
  --------------------------------------------------
  ------
• new new ext
  orig orig ext
  ESP ESP
• IP hdr hdrs ESP IP
  hdr hdrs TCP Data Trailer
  ICV

12
Outbound Packet Processing

• Security Association Lookup
• Packet Encryption and Integrity Check Value (ICV)
  Calculation
• 1. Separate Confidentiality and Integrity
  Algorithms
• the Sender proceeds as
• 1. Encapsulate (into the ESP Payload field)
  
• - for transport mode -- just the original next
  layer protocol information.
• - for tunnel mode -- the entire original IP
  datagram.
• 2. Add any necessary padding
• 3. Encrypt the result
• 4. Compute the ICV over the ESP packet minus the
  ICV field
• 2. Combined Confidentiality and Integrity
  Algorithms
• 1. Encapsulate into the ESP Payload Data field
  
• - for transport mode -- just the original next
  layer protocol information.
• - for tunnel mode -- the entire original IP
  datagram.
• 2. Add any necessary padding
• 3. Encrypt and integrity protect the result
• Sequence Number Generation
• Fragmentation

13
Inbound Packet Processing

• Reassembly
• Security Association Lookup
• Sequence Number Verification
• ESP permits two-stage verification of packet
  sequence numbers
• The preliminary Sequence Number check
• the integrity of the Sequence Number
• Integrity Check Value Verification
• Separate Confidentiality and Integrity Algorithms
  
• 1. If integrity has been selected, the receiver
  computes the ICV
• 2. The receiver decrypts the ESP Payload Data,
  Padding, Pad Length, and Next Header
• 3. The receiver processes any Padding
• 4. The receiver checks the Next Header field.
• 5. The receiver reconstructs the original IP
  datagram from
• - for transport mode -- outer IP header plus
  the original next layer protocol information in
  the ESP Payload field
• - for tunnel mode -- the entire IP datagram in
  the ESP Payload field.

14
Inbound Packet Processing

• Combined Confidentiality and Integrity
  Algorithms
• 1. Decrypts and integrity checks the ESP Payload
  Data, Padding, Pad Length, and Next
  Header
• 2. If the integrity check performed by the
  combined mode algorithm fails, the receiver must
  discard the received IP datagram as invalid
• 3. Process any Padding
• 4. The receiver checks the Next Header field
• 5. Extract the original IP datagram (tunnel
  mode) or transport-layer frame (transport mode)
  from the ESP Payload Data field.

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AUDITING

• No valid Security Association exists for a
  session
• A packet offered to ESP for processing appears to
  be an IP fragment
• Attempt to transmit a packet that would result in
  Sequence Number overflow
• The received packet fails the anti-replay checks
• The integrity check fails

16

• CONFORMANCE REQUIREMENTS and
• SECURITY CONSIDERATIONS

17
ESP IMPLEMENTATION USING AN ANTI-REPLAY WINDOW

• var. Name Size (bits) Meaning
• ------------- -----------
  ---------------------------
• W 32 Size of window
• T 64 Highest sequence
  number authenticated so far, upper bound of
  window
• Tl 32 Lower 32
  bits of T
• Th 32 Upper 32
  bits of T
• B 64 Lower
  bound of window
• Bl 32 Lower 32
  bits of B
• Bh 32 Upper 32
  bits of B
• Seq 64 Sequence
  number of received packet
• Seql 32 Lower 32
  bits of Seq
• Seqh 32 Upper 32 bits
  of Seq 

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• If (Tl gt W - 1)
• If (Seql gt Tl - W 1)
• Seqh Th
• If (Seql lt Tl)
• If (pass replay check)
  
• If (pass integrity check)
  Set bit corresponding to Seql
  Pass the packet on
• Else reject packet
• Endif
• Else reject packet
• Endif
• Else
• If (pass integrity check)
  
• Tl Seql (shift bits)
  
• Set bit corresponding to Seql
• Pass the packet on
  
• Else reject packet
• Endif
• Endif
• Else

• Else
• If (Seql gt Tl - W 1)
• Seqh Th - 1
• If (pass replay check)
  
• If (pass integrity check)
• Set the bit corresponding to
  Seql
• Pass packet on
  
• Else reject packet
• Endif
• Else reject packet
• Endif
• Else
• If (Seql lt Tl)
• If (pass replay check)
• If (pass integrity check)
  Set the bit
  corresponding to Seql
• Pass packet on
  
• Else reject packet
  
• Endif
• Else reject packet
  

19
REFERENCES

• Stephen Kent of BBN Technologies.
• "IP Encapsulating Security Payload (ESP)".
• An internet draft submitted to the IPsec
  Working Group, July 2002
• Draft-ietf-ipsec-esp-v3-05.txt expires Oct
  2003
• "http//www.ietf.org/internet-drafts/draft-i
  etf-ipsec-esp-v3-03.txt"
• R. Atkinson of Naval Research Laboratory.
• "IP Encapsulating Security Payload (ESP)"
• A paper submitted to the Network Working
  Group, August 1995
• "http//www.faqs.org/rfcs/rfc1827.html"
• Stephen Kent of BBN Corp and R. Atkinson of
  _at_Home Network.
• "Security Architecture for the Internet
  Protocol"
• A paper submitted to the Network Working
  Group, November 1998
• "http//www.ietf.org/rfc/rfc2401.txt"

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QUESTIONSand COMMENTS!!