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Chapter 6

Chapter 6. IP Security. IP Security. We have considered some application specific security mechanisms in last chapter eg. S/MIME, PGP, Kerberos however there are security concerns that cut across protocol layers would like security implemented by the network for all applications

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Chapter 6

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  1. Chapter 6 IP Security

  2. IP Security • We have considered some application specific security mechanisms in last chapter • eg. S/MIME, PGP, Kerberos • however there are security concerns that cut across protocol layers • would like security implemented by the network for all applications • The IP spoofing is a serious attack which creates false IP addresses and exploit application that use authentication based on IP.

  3. IPSec • general IP Security mechanisms • provides • authentication • confidentiality • key management • applicable to use over LANs, across public & private WANs, & for the Internet

  4. Examples of Application of IPSec • Secure Branch office connectivity over the internet: This enables a business to reply heavily on the internet and reduce its need for private networks, saving costs and network management overhead. • Secure remote access over the internet: Reduces the toll charges for employees and telecommuters • Establishing extranet and intranet connectivity with partners: used to secure communication in organizations, authentication and confidentiality • Enchancing electronic commerce security: use of IPSec enhances the security of electronic commerce applications that have built in security protocols

  5. IPSec Scenario

  6. Benefits of IPSec • in a firewall/router provides strong security to all traffic crossing the perimeter • is resistant to bypass • is below transport layer, hence transparent to applications • can be transparent to end users • can provide security for individual users if desired

  7. IP Security Architecture • specification is quite complex • defined in numerous RFC’s • incl. RFC 2401/2402/2406/2408 • many others, grouped by category • mandatory in IPv6, optional in IPv4

  8. IP Security Architecture

  9. IP Security Architecture • The documents are divided into seven group: • Architecture: covers the general concepts, security requirements, definition and mechanism defining IPSec technology • Encapsulating security payload (ESP): covers packet format and general issues related to ESP • Authentication Header: covers packet format and general issues related to AH • Encryption Algorithm: documents that describes how various encryption algorithm is used. • Authentication Algorithm: documents that describes how various encryption algorithm is used for AH • Key management: Documents that describe key management schemes. • Domain of Interpretation (DOI): contains value needed for the other documents to relate to each other.

  10. IPSec Services • Access control • Connectionless integrity • Data origin authentication • Rejection of replayed packets • a form of partial sequence integrity • Confidentiality (encryption) • Limited traffic flow confidentiality

  11. Security Associations • A one-way relationship between sender & receiver that affords security for traffic flow • defined by 3 parameters: • Security Parameters Index (SPI) • IP Destination Address • Security Protocol Identifier • has a number of other parameters • sequence number counter, sequence counter overflow, anti-replay window, AH & EH info, lifetime etc • have a database of Security Associations

  12. Authentication Header (AH) • 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

  13. Authentication Header

  14. Authentication Header • Next header (8bits):identifes the type of header immediately following this header • Payload length(8 bits): length of authentication header in 32 bit words minus 2 • Reserved (16 bits): for future use • Security parameters index (32 bits): identifies a security association • Sequence number(32bits): a monotonically increasing counter value • Authentication data (variable): A variable-length field that contains the integrity check value for this packet

  15. Encryption and Authentication Algorithms • Encryption: • Three-key triple DES • RC5 • IDEA • Three-key triple IDEA • CAST • Blowfish • Authentication: • HMAC-MD5-96 • HMAC-SHA-1-96

  16. Transport & Tunnel Modes

  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

  18. Encapsulating Security Payload

  19. Transport vs Tunnel 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

  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 (refer next slide)

  21. Combining Security Associations

  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

  23. Oakley key Determination Protocol • 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

  24. Features of Oakley • It employs a mechanism known as cookies to thwart clogging attacks • It enables the 2 parties to negotiate a group. • It uses nonces to ensure against replay attacks • It enables the exchange of diffie-hellman public key values • It authenticates the diffie-hellman exchange to thwart man-in-the-middle attacks.

  25. 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

  26. ISAKMP

  27. ISAKMP formats • Initiator cookie ( 64 bits) • Responder cookie (64 bits) • Next payload (8 bits) • Major version(4 bits) • Minor version( 4 bits) • Exchange type(8 bits) • Flags( 8 bits)

  28. Summary • have discussed : • IPSec security framework • AH • ESP • key management & Oakley/ISAKMP

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