Network systems security by mort anvari lecture11

Network Layer Security
Network Systems Security

Mort Anvari


Security in Network Layer
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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
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Two protocols
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Provide general security services for IP
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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
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Scenario of IPSec Uses

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Benefits of IPSec
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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

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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)
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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
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Security Parameters Index (SPI)
IP Destination Address
Security Protocol Identifier
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SA Parameters
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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)
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Provide support for data integrity and
authentication of IP packets
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Based on use of a MAC
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end system/router can authenticate
user/app
prevent address spoofing attacks by
tracking sequence numbers
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-toIntermediate Authentication

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Scope of AH
Authentication

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Encapsulating Security
Payload (ESP)
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Provide message content confidentiality
and limited traffic flow confidentiality
Can optionally provide the same
authentication services as AH
Support range of ciphers, modes,
padding
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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
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Transport mode is used to encrypt and
optionally authenticate IP data
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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
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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
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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
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Handle key generation and distribution
Typically need 2 pairs of keys
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Manual key management
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2 per direction for AH & ESP
sysadmin manually configures every system

Automated key management
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automated system for on demand creation
of keys for SA’s in large systems
Oakley and ISAKMP
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OAKLEY
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A key exchange protocol
Based on Diffie-Hellman key exchange
Add features to address weaknesses of
Diffie-Hellman
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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
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Three basic requirements
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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
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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
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Denial-of-Service (DoS) attack
Hop Integrity

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