Network Layer Security Network Systems Security Mort Anvari.

Network Layer Security Network Systems Security

Mort Anvari

9/30/2004 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

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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

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Scenario of IPSec Uses

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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

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IP Security Architecture Specification is quite complex Defined in numerous RFC’s

RFC 2401/2402/2406/2408 many others, grouped by category

Mandatory in IPv6, optional in IPv4

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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

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

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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

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Authentication Header

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

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Scope of AH Authentication

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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

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Encapsulating Security Payload

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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

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Scope of ESP Encryption and Authentication

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Combining Security Associations SAs can implement either AH or

ESP, but each SA can implement only one

To implement both, need to combine SAs form a security bundle

Have 4 cases

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Combining Security Associations

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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

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

Diffie-Hellman cookies to counter clogging attacks nonces to counter replay attacks key exchange authentication to counter

man-in-the-middle attacks Can use arithmetic in prime fields or

elliptic curve fields

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Usage of Cookies Three basic requirements

Must depend on specific parties Impossible for anyone other than issuing entity

to generate cookies that will be accepted by issuing party

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

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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

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ISAKMP

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Next Class Denial-of-Service (DoS) attack Hop Integrity