Network Security Chapter 7

CHAPTER 7

SECURITY IN NETWORKS AND DISTRIBUTED SYSTEM

INTRODUCTION Network is two devices connected across some

medium by hardware and software that complete the communications (simple definition of network).

User (Client)

Host Server

Communication medium

Simple View of Network

Introduction A network is normally not just single client to a

single server; typically many clients interact with many servers.

User (Client) Host Server

User (Client)User (Client)

User (Client)

Host Server

User (Client)User (Client)

User (Client)

System A

System B

Network Security IssuesNetwork have security problems for the following reasons: Sharing – resources and workload sharing Complexity of system Unknown parameter – expandability of a network also implies

uncertainty about the network boundary Many points of attack – file may past through many host before

reaching the destination Anonymity – attacker can mount an attack with touching the

system Unknown path – there may be many path from one host to

another.

Possible Network Security Threats Wiretapping Impersonation Message confidence violations Message integrity violations Hacking Denial of Service (DoS)

Possible Network Security ThreatsWiretapping Wiretap means to intercept communications. Passive / Active Wiretapping Packet sniffer can retrieve all packets on the net. “Inductance” is a process where an intruder can tap a

wire without making physical contact with the cable. Microwave and satellite – higher possibility of

interception due to wider broadcasting.

Possible Network Security ThreatsWiretapping Optical fiber offers two significant security

advantages: The entire optical network must be tuned carefully each

time a new connection is made. Therefore, no one can tap an optical system without detection.

Optical fiber carries light energy, not electricity. Light does not emanate a magnetic field as electricity does. Therefore an inductive tap is impossible on an optical fiber cable.

Possible Network Security ThreatsWiretapping However, optical fiber also has weaknesses

where wiretappers will try to tap at the repeaters, splices and other equipments that connects to the fiber optic and thus creates vulnerabilities.

Possible Network Security ThreatsImpersonation Pretend to be someone (personnel) or something

(process). In an impersonation, the attacker has several choices:

Guess the identity and authentication details of the target Pick up the identity and authentication details of the target

from a previous communication Circumvent or disable the authentication mechanism at

the target computer Use a target that will not be authenticated Use a target whose authentication data is known

Possible Network Security ThreatsMessage Confidentiality Violations Misdelivery Exposure Traffic Flow Analysis

Possible Network Security ThreatsMessage Integrity Violations Falsification of Messages

Change the content of a message Change any part of the content of a message Replace a message entirely Redirect a message Destroy or delete the message

Noise – unintentional interference

Possible Network Security ThreatsHacking A source of threat to security in computer

communication. Hacker is considered as a separate threat because a

hacker can develop tools to search widely and quickly for particular weaknesses and move swiftly to exploit weaknesses.

In this way, hacker has unlimited time to analyze, plan, code, simulate and test for future attack.

In reviewing the effects of this attack ; if it succeeds, what additional capability would that give the hacker for future attacks?

Possible Network Security ThreatsDenial of Service Result of any action or series of actions that

prevents any part of a telecommunications system from functioning.

Connectivity Flooding Routing problems Disruption of Service

Network Security Control Encryption – link encryption, end-to-end encryption Link Encryption:

Data is encrypted just before the system places it on the physical communication links.

Decryption occurs just as the communication enters the receiving computer.

Application

Presentation

Session

Transport

Network

Data Link

Physical

Sender ReceiverMessageIntermediate

Host

Message

(Plaintext)

Exposed

Message Encrypted Message in Plaintext: Exposed

Link Encryption

Network Security Control End-to-end encryption:

Provides security from one end of a transmission through the other.

Application

Presentation

Session

Transport

Network

Data Link

Physical

Sender Message

Intermediate

Host

Message Encrypted Message in Plaintext: Exposed

Receiver

End-to-End Encryption

Network Security ControlLink Encryption versus End-to-end Encryption:

Link Encryption End-to-end Encryption

Security Within HostsMessage exposed in the sending hostMessage expose in intermediate nodes

Security Within HostsMessage encrypted in sending hostMessage encrypted in intermediate nodes

Role of UserApplied by sending hostInvisible to userHost maintains encryptionCan be done in hardwareAll or no messages encrypted

Role of UserApplied by sending processUser applies encryptionUser must find algorithmSoftware implementationUser chooses to encrypt or not, for each message

Authentication Issues in Distributed System

There are two main concern regarding authentication

issue in distributed system which are:

(1) How to ensure the authenticity of the communicating hosts?

(2) How to ensure authenticity of users who are using the hosts?


That is by using: Digital Distributed Authentication DCE (Distributed Computer Environment) Kerberos SESAME CORBA


Kerberos Is a system that supports authentication in distributed

systems. Was designed at Massachusetts Institute of

technology. The basis of kerberos is a central server that provides

authenticated tokens called tickets to requesting applications.


KERBEROSInitiating a Kerberos Session:

Authentication Issues in Distributed SystemKERBEROS

Obtaining a Ticket to Access a File:

KERBEROS:Access to Services and Servers in Kerberos


Kerberos was carefully designed to withstand attacks in

distributed environments:

No password communicated on the network Cryptographic protection against spoofing Limited period of validity Time stamps to prevent replay attacks Mutual authentication

Authentication Issues in Distributed System Kerberos is not a perfect answer to security

problems in distributed systems because: Kerberos requires continuous availability of a trusted

ticket granting server. Authenticity of servers requires a trusted relationship

between the ticket granting server and every server Kerberos requires timely transactions A subverted workstation can save and later replay user

passwords


Kerberos is not a perfect answer to security problems in distributed systems because: Password guessing works Kerberos does not scale well Kerberos is not a complete solution

Privacy Enhanced Electronic Mail (PEM)

The basis of PEM is encryption. In order to send a PEM message the sender

must have a certificate for the receiver.

Message header

+ Body

Message

Encryption

key

Receiver’s

public key

New header

Encrypted data

Encrypted key

Encrypted Message Header + Body

Public key encryption

Symmetric key encryption

Compose message

PEM processing requested ?

PEM

Send messageReceive message

Privacy enhanced ?

PEM

View message

Yes

No

Yes

No

PEM processing in Message Transmission

Privacy Enhanced Electronic Mail (PEM)

The major problem with PEM is key management. Therefore PGP was designed to overcome this

problem.

Pretty Good Privacy (PGP) Was designed by Phil Zimmerman to offer a reasonable

degree of privacy for email. It uses a message structuring scheme similar to PEM. The key management for PGP is ad hoc. Each user has a set of people he or she knows and trusts. The user exchanges public keys with those friends, exactly as

one might swap business card at meeting. Some people accept not just the friends’ public key but also

all public keys their friends have.

Pretty Good privacy (PGP)

The assumption here is that any friend of yours is a friend of mine.

A PGP user builds a key ring which is the set of all public keys that person possesses.

In that way, when an encrypted messages arrives, the person can decrypt it if the key is on that person’s key ring.

Firewalls A firewall is a process that filters all traffic between

a protected or “inside” network and a less trustworthy or “outside” network.

There are three types of firewall: Screening Routers Proxy gateways Guards

FirewallsScreening Router Is the simplest and in some situations the most effective type

of firewall. Hosts tend not to be connected directly to a wide area

network; more often hosts are connected to a router.

Firewalls

Router joining LAN to two WANs

FirewallsScreening Router Router will only see the header of the message. Header will contain information on:

The sender/receiver address Protocol Port Length of a packet

It can also control the traffic based on application – by using port numbers (eg: 21 for FTP and 25 for SMTP)

It can also decide which application is acceptable and not acceptable.

It can also determine the authentication of an inside address.

FirewallsProxy Gateway Is also called a bastion host. Is a firewall that simulates the (proper) effects

of an application so that the application will receive only requests to act properly.

FirewallsProxy Gateway To understand the real purpose of a proxy

gateway, we consider some examples: A company wants to set up an online lists so that

outsiders can see the products and prices offered. It wants to be sure that no outsider can change the prices or product list and that outsiders can access only the price list not any of the more sensitive files stored inside.

FirewallsGuard A guard is a sophisticated proxy firewall. The guard decides what services to perform on the

user’s behalf based on its available knowledge such as whether it can reliably know of the (outside) user’s identity, previous interactions and so forth.

FirewallsGuard Here are some more sophisticated examples of guard

activities: A university wants to allow its students to use email up to

a limit of so many messages or so many characters of email in the last so many days. Although this result could be achieved by modifying email handlers it is more easily done by monitoring the common point through which all email flows (the mail transfer protocol).

A school wants its students to be able to access the WWW but because of the slow speed of its connection to the Web it will allow only so many characters per download image.

FirewallsFirewalls are not complete solutions to all computer security problems. Firewalls can protect an environment only if the firewalls

control the entire perimeter. Firewall do not protect data outside the perimeter. Firewall are the most visible part of an installation to the

outside and therefore is the most attractive point of attack. Firewalls are targets of penetrators. Firewalls must be correctly configured. Firewalls exercise only minor control over the content

admitted to the inside – inaccurate data or malicious code must be controlled inside the perimeter.

Network Security Chapter 7

Technology