CSCE 715 Network Systems Security Chin-Tser Huang huangct cse

CSCE 715: Network Systems Security Chin-Tser Huang huangct@cse. sc. edu University of South Carolina 9/29/2005

Security in Network Layer n n n 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 9/29/2005 2

IPSec n Two protocols n n n Provide general security services for IP n n n Authentication Header (AH) Encasulating Security Payload (ESP) Authentication Confidentiality Anti-replay Key management Applicable to use over LANs, across public and private WANs, and for the Internet 9/29/2005 3

Scenario of IPSec Uses 9/29/2005 4

Benefits of IPSec n n n 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 9/29/2005 5

IP Security Architecture n n Specification is quite complex Defined in numerous RFC’s n n n RFC 2401/2402/2406/2408 many others, grouped by category Mandatory in IPv 6, optional in IPv 4 9/29/2005 6

Security Association (SA) n n n 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 n n n Security Parameters Index (SPI) IP Destination Address Security Protocol Identifier 9/29/2005 7

SA Parameters n n n n Sequence Number Counter Sequence Number Overflow Anti-Replay Window AH and ESP information Lifetime IPSec Protocol Mode Path MTU 9/29/2005 8

Authentication Header (AH) n Provide support for data integrity and authentication of IP packets n n n Based on use of a MAC n n n end system/router can authenticate user/app prevent address spoofing attacks by tracking sequence numbers HMAC-MD 5 -96 or HMAC-SHA-1 -96 MAC is calculated over IP header fields that are either immutable or predictable, AH header other than authentication data, and entire upper-level protocol data Parties must share a secret key 9/29/2005 9

Authentication Header 9/29/2005 10

End-to-End vs End-to-Intermediate Authentication 9/29/2005 11

Scope of AH Authentication 9/29/2005 12

Encapsulating Security Payload (ESP) n n n Provide message content confidentiality and limited traffic flow confidentiality Can optionally provide the same authentication services as AH Support range of ciphers, modes, padding n n n DES, Triple-DES, RC 5, IDEA, CAST etc CBC most common pad to meet blocksize, for traffic flow 9/29/2005 13

Encapsulating Security Payload 9/29/2005 14

Transport vs Tunnel Mode ESP n Transport mode is used to encrypt and optionally authenticate IP data n n data protected but header left in clear can suffer from traffic analysis but is efficient good for ESP host to host traffic Tunnel mode encrypts entire IP packet n n n add new header for next hop can counter traffic analysis good for VPNs, gateway to gateway security 9/29/2005 15

Scope of ESP Encryption and Authentication 9/29/2005 16

Combining Security Associations n n SAs can implement either AH or ESP, but each SA can implement only one Some traffic flows may require services of both AH and ESP, while some other flows may require both transport and tunnel modes To address these concerns, need to combine SAs to form a security association bundle Have 4 basic cases 9/29/2005 17

Combining Security Associations 9/29/2005 18

Key Management n n Handle key generation and distribution Typically need 2 pairs of keys n n Manual key management n n 2 per direction for AH & ESP sysadmin manually configures every system Automated key management n n automated system for on demand creation of keys for SA’s in large systems Oakley and ISAKMP 9/29/2005 19

OAKLEY n n n A key exchange protocol Based on Diffie-Hellman key exchange Add features to address weaknesses of Diffie. Hellman n n cookies to counter clogging attacks nonces to counter replay attacks key exchange authentication to counter man-inthe-middle attacks Can use arithmetic in prime fields or elliptic curve fields 9/29/2005 20

Usage of Cookies n Three basic requirements n n Must depend on specific parties Impossible for anyone other than issuing entity to generate cookies that will be accepted by issuing entity Cookie generation and verification must be fast To create a cookie, perform a fast hash over src and dst IP addresses, src and dst ports, and a locally generated secret value 9/29/2005 21

ISAKMP n n 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 9/29/2005 22

ISAKMP 9/29/2005 23

Next Class n n Denial-of-Service (Do. S) attack Hop Integrity 9/29/2005 24