Ecommerce Lecture By Sir Adnan

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Nov 21, 2013 (4 years and 5 months ago)


Ecommerce Lecture By Sir Adnan



A firewall is a combination of hardware and software that sits betwe
en the internet and internal network of an
organization to protect the network from outside attack (Fig. 1).

It can examine the data entering or leaving from the network and can filter the data according to certain rules,
thus, protects the network from a
n attack.

There are three main types of firewalls detailed as follows:

Packet filter firewall

A packet filter firewall is the
simplest type of firewalls

which operates at
data link and network layers

the OSI model.

It uses a set of rules to determine
whether outgoing or incoming data packets are allowed to pass through the

For example, we can, as a rule, specify IP addresses of sending devices such that packets from these IP
addresses are not allowed to enter the network. The Firewall would
stop them from entering.

Circuit level firewall

It is quite similar to the packet filter firewall. It also works on the basis of a set of rules for filtering packets
but operates at the
transport layer

of the OSI Model so has
greater functionality

As a

rule, the
higher the layer of OSI model where a firewall operates
, the more sophisticated is the
firewall. It can make packets sent from internal network to a destination outside the firewall appear as if they
originated at the firewall. Thus information
regarding hosts on the internal network remains secret. It can also
determine whether TCP/IP connection between a host and a machine outside firewall has been properly
established. Thus it can cut off any connection which has been hijacked by a hacker tryi
ng to pass through
the firewall.

Application gateway firewall

It operates at
application layer of the OSI Model.

It uses strong user authentication to verify identity of a
host attempting to connect to the network using application layer protocols such us

FTP. In contrast to
packet filter firewall,
it filters the requests rather than packets entering/leaving the network
. It can
block any outgoing HTTP or FTP requests. It can prevent employees of a company inside a firewall from
downloading potentially dang
erous programs from the outside. In other words, this type of firewall is used to
control connections thus employees of a company can be restricted from connecting to certain web sites.

We can combine circuit level capabilities with application gateway services to form Hybrid type of a firewall.

Proxy server

A proxy server sits between an internal trusted network and the untrusted network, that is, internet,
as you
can see in Fig. 2 belo

Mainly, it can do three things:

An http request from the browser goes to proxy server. It can affix its own IP address instead of IP address
of the requesting machine; thus, it hides the information of the host. It downloads the requested page itself
nd afterwards supplies it to the user.

It can also act as a firewall filtering requests for certain web pages.

An important job it can do is to
speed up the processing of http requests by caching web pages

Caching means that it can store the requested we
b pages in its memory (cache memory) for certain period.
The advantage of caching is that for subsequent web page requests the time of supply of the web pages is
reduced. Instead of sending the request to actual web server, the proxy server can quickly sup
ply the web
page stored in its cache memory, thus, it saves the time of downloading the page.

Virtual private network (VPN)

Ecommerce Lecture By Sir Adnan


Suppose that a client is sitting at a local branch network of a company and wants to become part of a bigger,
head office network o
f that company located far away. One option for him is to set up a dial up connection,
which means that he can be connected to a server machine lying in the head office network through a direct
telephone line. That server machine may be called a
Remote Acc
ess Server (RAS)
and the client may be
called a
Remote Access Client (RAC).
Remote access is a two way process so both RAS and RAC must be
configured, first. Some windows operating systems provide the facility to configure the RAS and RAC.
Basically, the c
lient specifies the phone no. of RAS while configuring. After both RAS and RAC are
configured, the client enters identification information (password etc.) and clicks at “Dial”. Accordingly,
phone no. of RAS is dialed and connection with RAS is setup. Once

clients are connected to RAS, they can
access the remote company network and its resources

servers, printers etc.

A protocol, Point to Point Protocol (PPP), is used to set up the dial up connection between RAC and RAS
for exchange of data packets.

N provides another option of remote access. It is defined as a secure, dedicated point to point
connection over the internet. In VPN we use internet infrastructure for connection instead of a special
telephone line. Both RAS (also called tunnel server) and

RAC (also called tunnel client) are connected to the
internet. Initially, both are configured for VPN. IP address of tunnel server must be specified during the
configuration of tunnel client (instead of phone no.). The option of VPN is available if we exp
lore the menu
‘Internet Options’. We can enable VPN, thus. Similarly, tunnel server should also be configured so that a
client’s request for access can be authenticated. VPN connections or tunnels are managed by Point to Point
Tunneling Protocol (PPTP) whi
ch due to encryption provides secure transport of private communications
over the public internet. A VPN connection thus can be created between the branch office and the corporate
head office.

VPN is a cost saving measure as compared to simple remote acces
s using dial up connection. In VPN one
makes a local call to the ISP and then using ISP’s infrastructure, routers etc. one is connected to the internet.
In other words a client can become part of the remote network through the internet. Note that a tunnel
just incurs the cost of a local call to the ISP and yet he can remain part of the remote corporate network for
many hours. On the other hand, in case of dial up connection for remote access one has to pay` the cost of a
long distance call for as man
y no. of hours as one wants to be connected to the remote corporate network.
This is going to be very expensive. VPN is the example of an extranet. You know that when two or more
intranets are connected to each other they form an extranet. A manufacturing
company thus can be
connected to its suppliers of raw material and its distributors through VPN.


the biggest challenge

There is a consensus that the issue of computer and data security is the biggest hurdle in the growth of

Web serve
rs also face this security threat.

Programs that run on a server have the potential to damage databases, abnormally terminate server software
or make changes in the information placed there. A number of international organizations have been formed
to shar
e information and combat security threats to computers and computer networks. The names of two
such organizations are worth

Computer Emergency Response Team (CERT)

Systems Administrator, Audit, Network and Security Institute (SANS Institute)

he best response that the experts have come up with to tackle the security issue is in terms of cryptography.


Cryptography is the technique of converting a message into unintelligible or non
understandable form such

that even if some unauthorized or unwanted person intercepts the message he/she would still not be able to

make any sense out of it. Cryptography is thousands of years old.

Techniques used for cryptography Substitution In substitution we replace each lett
er in the message with

another to make the message non
understandable. For example, each letter “a” in the message can be

Ecommerce Lecture By Sir Adnan


replaced with letter “d” and letter “b” with letter “e” and so on.

Transposition It is based on scrambling the characters in a messag
e. A transposition system may first write a
message into a table row by row then the message can be read and rewritten column by column to make it
(see Fig. 3).

Historically, cryptography has long been used as a military technology. Julis Ceaser

used a simple
transposition cipher to scramble messages to give instructions to his commanders in the battlefield. Similarly,
Hitler used Enigma encryption cipher to scramble messages sent by radio to German armies and u
during the Second World War.

Cryptography has also been used for non
military purposes over the centuries.
There are records of people using cryptography to protect religious secrets and to hide secrets of science and
industry. In recent years, the use of cryptography in business and

commerce appears to have surpassed its
earlier use. It has made the rapid commercialization of internet possible. Without cryptography, it is doubtful
that banks, businesses and individuals would feel safe doing business online.