Encapsulation Security Payload - PowerPoint PPT Presentation

View by Category
About This Presentation
Title:

Encapsulation Security Payload

Description:

4. R. Anderson. Security Engineering. A Guide to Building Dependable Distributed Systems. ... 5. IPSEC and Windows 2000: a step by step guide ... – PowerPoint PPT presentation

Number of Views:525
Avg rating:3.0/5.0
Slides: 19
Provided by: lanv
Learn more at: http://www.cs.sjsu.edu
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Encapsulation Security Payload


1
  • Encapsulation Security Payload
  • Protocol
  • Lan Vu

2
OUTLINE
  • Introduction and terms
  • 2. ESP Overview
  • ESP Packet Format
  • ESP Fields
  • ESP Modes
  • ESP packet processing
  • Why ESP?
  • Security Considerations
  • ESP Performance Impacts
  • Conclusion

3
INTRODUCTION AND TERMS
  • Internet Protocol Security (IPSec) a security
    function implemented at the IP level of the
    protocol stack.
  • Security Association (SA) is used to track a
    given communication session. It defines the
    information about the traffic security protocol,
    the authentication algorithm, and the encryption
    algorithm to be used. Also, it gives the
    information on data flow, lifetime of the SA and
    sequence numbering to guard against replay
    attacks.

4
ESP OVERVIEW
  • ESP protocol (i.e. traffic security protocol) is
    used in an IPsec transmitted over IP.
  • ESP is identified by protocol number 50.
  • ESP provides optional services to provide the
    protection for anything such as authentication,
    encryption, and integrity check for IP datagrams.
    It operates on a per-packet basis.
  • Encryption scrambles the data packet to
    prevent unauthorized people from reading the
    message.
  • Authentication verifies that the source
    address was not forged.
  • Anti replay mechanism ensures the packet was
    not tampered while in route to its destination.

5
ESP OVERVIEW (cont.)
  • The desired services to be used are selectable
    upon establishment of the security association
    (SA).
  • Encryption is selectable independent of any other
    services. If encryption is enabled, then
    integrity check and authentication should be
    turned on as well. If only encryption is used,
    intruders could forge packets in order to mount a
    cryptanalytic attack.

6
ESP PACKET FORMAT
  • There is an ESP header, an ESP trailer, and ESP
    authentication data. The payload is located
    (encapsulated) between the header and the
    trailer, which gives the protocol its name.

7
PACKET FIELDS
  • The ESP packet contains the following fields
  • Security Parameter Index (SPI) This field is 32
    bits in length
  • Sequence Number This 32-bit field is an
    increasing counter, and again follows the AH
    definitions. It is used to prevent replay
    attacks.
  • Payload Data This field is mandatory.
  • It consists of a variable number of bytes of
    data described by the Next Header field.
  • PD is encrypted with the cryptographic
    algorithm selected during SA establishment. If
    the algorithm requires initialization vectors
    (CBC), they will be included here as well.
  • Algorithms supported
  • DES (CBC) TDEA (three key)
  • IDEA Three key triple IDEA
  • CAST Blowfish
  • RC5

8
PACKET FIELDS (CONT.)
  • Padding
  • ie. to ensure that the bits to be encrypted are
    a multiple of blocksize
  • Authentication Data This optional field is
    variable in length.
  • Authenticate packet using MD5 or SHA-1 with a
    key (i.e. HMAC) or without a key to create a
    unique hash or digest of the contents of the
    packet.
  • IP header is not covered in the AD
  • The AD is calculated from the SPI to the Next
    Header field inclusive.

9
ESP MODES
  • Transport Mode Here the ESP header is inserted
    immediately after the IP header. The ESP trailer
    and the optional authentication data are appended
    to the payload. In transport mode, ESP neither
    authenticates nor encrypts the IP header. But
    this mode has a low computational overhead.

10
ESP MODES (CONT.)
  • Tunnel Mode Here, a new IP packet is made with a
    new IP header. ESP/Transport is then applied and
    the original datagram is the payload for the new
    packet. If authentication and encryption have
    been initiated, the packet is protected. However,
    the new IP header is not protected.

11
ESP PACKET PROCESSING
  • Sender Processes
  • Look up SA
  • Packet encryption and authentication data
  • Encapsulate the original next layer protocol
    information or the entire original IP datagram
  • Add necessary padding
  • Encrypt the result using the key and encryption
    algorithm mode specified in SA
  • Compute the authenticate data over the ESP
    packet using hash functions.
  • 3. Generate sequence number

12
ESP PACKET PROCESSING
  • Receiver Processes
  • Determines the appropriate SA
  • Verify sequence number
  • Verify the decryption and authentication
  • Decrypts and integrity check the ESP payload
    data, padding, pad length, and next header using
    the key, algorithm, algorithm mode indicated by
    SA
  • If the check fail, discard the packet and log
    the SPI value, date/time received, source
    address, destination address, the sequence
    number.
  • Process any padding
  • Check the next header field, if the value is
    59, the packet is discard .
  • Extract the original IP datagram or
    transport-layer fram from the ESP Payload Data
    field.

13
WHY ESP?
  • Data origin authentication is a security service
    that verifies the identity of the claimed source
    of data
  • Confidentiality is the security service that
    protects data from unauthorized parties.
  • the disclosure of application level data is
    protected by encrypting the payload data .
  • the disclosure of external characteristics of
    communication, also known as the traffic-flow
    confidentiality that is support by concealing
    source and destination addresses, message length,
    or frequency of communication.
  • Anti-replay detects arrival of duplicate IP
    datagram (using sliding receive window). It is
    supported by the sequence number which is an
    unsigned 32-bit field contains a monotonically
    increasing counter value in ESP header

14
SECURITY CONSIDERATIONS
  • The quality of the security provides by this ESP
    mechanism depends on
  • - The strength of the implemented cryptographic
    algorithms
  • - The strength of the key being used
  • - The correct implementation of the
    cryptographic algorithms
  • - The security of the key management protocol
  • - The correct implementation of IP
  • - Several security mechanisms in all of the
    participating systems.
  • The ESP protocol is described as a security
    service focuses only on the IP layer. Not solve
    the secure of the system.

15
SECURITY CONSIDERATIONS (cont.)
  • Advantage
  • Higher-level services protect a single
    protocol.
  • Lower level services protect a single medium.
  • Therefore, Can protect any protocol running
    above IP and any medium which IP runs over.
  • Attacks on higher-level protocols more
    difficult.
  • Limitations
  • Not end-to-end
  • Authenticate machine not users
  • Does not stop traffic analysis
  • In general, to provide an effective security
    environment, one should consider the combination
    of different mechanisms and algorithms as well as
    weight the strength and weakness for each of them
    to meet his or her needs.

16
PERFORMANCE IMPACTS
  • The encapsulating security approach used by ESP
    can noticeably impact network performance in
    participating systems
  • Protocol processing in participating systems will
    be more complex when encapsulating security is
    used, requiring both more time and more
    processing power.
  • Use of encryption will also increase the
    communications latency. The increased latency is
    primarily due to the encryption and decryption
    required for each IP datagram containing an
    Encapsulating Security Payload

17
Conclusion
  • Encapsulating Security Payload covers packet
    format and general issues for packet encryption.
    It offers the security service at the IP layer.
    Hence, it could be used in the conjunction with
    other security mechanisms in designing robust
    distributed systems.

18
REFERENCES
  • 1. R. Atkinson. IP encapsulating security
    payload (ESP). Request for Comments (Proposed
    Standard) RFC 1827, Internet Engineering Task
    Force, August 1995.
  • 2. FreeS/Wan Project. http//www.freeswan.org
  • 3. S. Kent and R. Atkinson. IP Encapsulating
    Security Payload. Request for Comments (2406),
    Internet Engineering Task Force, November 1998.
    http//www.networksorcery.com/enp/rfc/rfc2406.txt
  • 4. R. Anderson. Security Engineering. A Guide to
    Building Dependable Distributed Systems. Wiley,
    p.378, 2001.
  • 5. IPSEC and Windows 2000 a step by step guide
  • http//www.ccs.neu.edu/home/peterm/IPSEC2000.html
About PowerShow.com