This document discusses network security standards organizations like NIST and ISO, as well as key security concepts like threats, attacks, security services, and security mechanisms. It provides examples of cryptographic techniques like symmetric and public key encryption. It also summarizes standards for wireless security under IEEE 802.11i and the use of firewalls to filter network traffic and protect sites.

1. NETWORK SECURITY Lecture - 07

2. STANDARDS ORGANIZATIONS
National Institute of Standards & Technology (NIST)
Internet Society (ISOC)
International Telecommunication Union
Telecommunication Standardization Sector (ITU-T)
International Organization for Standardization (ISO)

3. PROBLEM
Computer networks are typically a shared resource used by
many applications representing different interests.
The Internet is particularly widely shared, being used by
competing businesses, mutually antagonistic governments,
and opportunistic criminals.
Unless security measures are taken, a network conversation
or a distributed application may be compromised by an
adversary.

4. COMPUTER SECURITY
the protection afforded to an automated information system
in order to attain the applicable objectives of preserving the
integrity, availability and confidentiality of information system
resources (includes hardware, software, firmware,
information/data, and telecommunications)

5. KEY SECURITY CONCEPTS

6. LEVELS OF IMPACT
can define 3 levels of impact from a security breach
Low
Moderate
High

7. ASPECTS OF SECURITY
consider 3 aspects of information security:
 security attack
 security mechanism
 security service
Terms in security
 threat – a potential for violation of security
 attack – an assault on system security, a deliberate attempt to evade
security services

8. PASSIVE ATTACKS

9. ACTIVE ATTACKS

10. SECURITY SERVICE
enhance security of data processing systems and information
transfers of an organization
intended to counter security attacks
using one or more security mechanisms
often replicates functions normally associated with physical
documents
which, for example, have signatures, dates; need protection from
disclosure, tampering, or destruction; be notarized or witnessed;
be recorded or licensed

11. SECURITY SERVICES
X.800:
“a service provided by a protocol layer of communicating
open systems, which ensures adequate security of the
systems or of data transfers”
RFC 2828:
“a processing or communication service provided by a
system to give a specific kind of protection to system
resources”

12. SECURITY MECHANISM
feature designed to detect, prevent, or recover from a
security attack
no single mechanism that will support all services
required
however one particular element underlies many of the
security mechanisms in use:
cryptographic techniques

13. MODEL FOR NETWORK
SECURITY

14. MODEL FOR NETWORK
SECURITY
 using this model requires us to:
1. design a suitable algorithm for the security
transformation
2. generate the secret information (keys) used by the
algorithm
3. develop methods to distribute and share the secret
information
4. specify a protocol enabling the principals to use the
transformation and secret information for a security
service

15. MODEL FOR NETWORK ACCESS
SECURITY

16. CRYPTOGRAPHIC BUILDING
BLOCKS
Symmetric-key encryption and decryption

17. CRYPTOGRAHIC BUILDING
BLOCKS
Encryption transforms a message in such a way that it
becomes unintelligible to any party that does not have the
secret of how to reverse the transformation.
The sender applies an encryption function to the original
plaintext message, resulting in a cipher text message that is
sent over the network.
The receiver applies a secret decryption function–the inverse
of the encryption function–to recover the original plaintext.

18. CRYPTOGRAPHIC BUILDING
BLOCKS
Symmetric Key Ciphers
both participants in a communication share the same key.
if a message is encrypted using a particular key, the same
key is required for decrypting the message.

19. CRYPTOGRAPHIC BUILDING
BLOCKS
Public-key encryption

20. CRYPTOGRAPHIC BUILDING
BLOCKS
Authentication using public keys

21. EXAMPLE SYSTEMS
Secure Shell (SSH)
Using SSH port forwarding to secure other TCP-based

22. WIRELESS SECURITY (IEEE
802.11I)
The IEEE 802.11i standard provides authentication, message
integrity, and confidentiality to 802.11 (Wi-Fi) at the link layer.
WPA2 (Wi-Fi Protected Access 2) is often used as a synonym for
802.11i, although it is technically a trademark of The Wi-Fi Alliance
that certifies product compliance with 802.11i.
802.11i authentication supports two modes. In either mode, the
end result of successful authentication is a shared Pairwise Master
Key.
Personal mode, also known as Pre-Shared Key (PSK) mode,
provides weaker security but is more convenient and economical
for situations like a home 802.11 network.
The wireless device and the Access Point (AP) are preconfigured
with a shared passphrase—essentially a very long password—from
with the Pairwise Master Key is cryptographically derived.

23. EXAMPLE SYSTEMS
Wireless Security (IEEE 802.11i)
Use of an Authentication Server in 802.11i

24. FIREWALLS
A firewall is a system that typically sits at some point of
connectivity between a site it protects and the rest of the
network.
It is usually implemented as an “appliance” or part of a
router, although a “personal firewall” may be implemented on
an end user machine.
Firewall-based security depends on the firewall being the only
connectivity to the site from outside; there should be no way
to bypass the firewall via other gateways, wireless
connections, or dial-up connections.

25. FIREWALLS
Firewalls filter based on IP, TCP, and UDP
information, among other things.
They are configured with a table of addresses that
characterize the packets they will, and will not,
forward.
Generally, each entry in the table is a 4-tuple:
 It gives the IP address and TCP (or UDP) port number for both the source
and destination.

26. FIREWALLS
A firewall filters packets flowing between a site and the rest of
the Internet