ppt

CSCE 790:Computer Network Security

Chin-Tser Huanghuangct@cse.sc.edu

University of South Carolina

9/30/2003 2

Security in Network Layer Implementing security in application layer

provides flexibility in security policy and key management

Problem is need to implement security mechanism in every application individually

To reduce the overhead, implement security in network layer to provide security for all applications between selected pair of computers

9/30/2003 3

IPSec Two protocols

Authentication Header (AH) Encasulating Security Payload (ESP)

Provide general security services for IP Authentication Confidentiality Anti-replay Key management

Applicable to use over LANs, across public and private WANs, and for the Internet

9/30/2003 4

Scenario of IPSec Uses

9/30/2003 5

Benefits of IPSec Provide strong security to all traffic

crossing the perimeter if installed in a firewall/router

Resistant to bypass IPSec is below transport layer, hence

transparent to applications Can be transparent to end users Can provide security for individual users

if desired

9/30/2003 6

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

9/30/2003 7

Security Association (SA) A unidirectional relationship between

sender and receiver that affords security for traffic flow

Each IPSec computer maintains a database of SA’s

Defined by 3 parameters Security Parameters Index (SPI) IP Destination Address Security Protocol Identifier

9/30/2003 8

SA Parameters

Sequence Number Counter Sequence Number Overflow Anti-Replay Window AH and ESP information Lifetime IPSec Protocol Mode Path MTU

9/30/2003 9

Authentication Header (AH) Provide support for data integrity and

authentication of IP packets end system/router can authenticate

user/app prevent 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

9/30/2003 10

Authentication Header

9/30/2003 11

End-to-End vs End-to-Intermediate Authentication

9/30/2003 12

Scope of AH Authentication

9/30/2003 13

Encapsulating Security Payload (ESP)

Provide message content confidentiality and limited traffic flow confidentiality

Can optionally provide the same authentication services as AH

Support range of ciphers, modes, padding DES, Triple-DES, RC5, IDEA, CAST etc CBC most common pad to meet blocksize, for traffic flow

9/30/2003 14

Encapsulating Security Payload

9/30/2003 15

Transport vs Tunnel Mode ESP Transport mode is used to encrypt and

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

9/30/2003 16

Scope of ESP Encryption and Authentication

9/30/2003 17

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

9/30/2003 18

Combining Security Associations

9/30/2003 19

Key Management Handle key generation and 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

Oakley and ISAKMP

9/30/2003 20

OAKLEY A key exchange protocol Based on Diffie-Hellman key exchange Add features to address weaknesses of

Diffie-Hellman cookies, groups (global parameters),

nonces, DH key exchange with authentication

Can use arithmetic in prime fields or elliptic curve fields

9/30/2003 21

ISAKMP Internet Security Association and Key

Management Protocol Provide framework for key management Define procedures and packet formats

to establish, negotiate, modify, and delete SAs

Independent of key exchange protocol, encryption algorithm, and authentication method

9/30/2003 22

ISAKMP

9/30/2003 23

Next Class

Denial-of-Service (DoS) attack Hop Integrity