Describe Digital Signatures and Firewalls

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 Digital Signature

Digital signature authenticates the identity of the sender of a message or signature holder
of the document. It ensures that the contents of the message are intact. The sender cannot
repudiate it later on. Digital Signatures are easily transportable. They cannot be imitated.
They can be automatically time stamped.

As per Information Technology Act, 2000, Digital Signature may be defined as
authentication of any electronic record by a subscriber by means of an electronic method or procedure in accordance with the provision of concerned sections of the Act.

IT Act provides the conditions subject to whom any electronic record(s) may be
authenticated by means of affixing digital signature.

TCS, Safes crypt and MTNL are some of the digital signature certifying authorities in
India licensed by the Controller of Certifying Authorities, Government of India.

The following are various steps in the working of a digital signature:

(a) Sender creates the message (electronic record).

(b) Electronic record is converted into message digest by using a mathematical
function known as hash function (which freezes the message).

(c) The message digest is encrypted with the sender's private key.

(d) Sender sends the message.

(e) Receiver receives the message.

(t) Receiver decrypts the message by the sender's public key.

(g) Receiver verifies the message.


Firewall is a hardware or software based security system that filters the packets and
prevents some packets from entering the network based on a security policy. A firewall
allows to establish certain rules to determine what traffic should be allowed in or out of
the private network. All data entering or leaving the Intranet pass through the firewall,
which examines each packet and blocks those that do not meet the specified security
criteria. It acts as a gatekeeper and protects a computer network from unauthorized and
malicious access.

A firewall may be hardware or software or both.

• Hardware firewalls can be found in broadband routers and is an important
part of network setup. It protects Computer on the local network. Software
firewalls are installed on the Computer and can be customized to incorporate
protection features.

The following are four mechanisms used by firewalls (refer to Table 6.2):
• Packet filter firewalls
• Stateful inspection firewalls-
• Proxy server firewalls, and
• Application level firewalls.

BasisPacket Filter
Proxy Server
Application Level
EvaluationEvaluates the headers
of incoming and outgoing packets
Evaluates the state
of TCP connection.
Act as intermediary
between internal
and external IP
addresses &blocks
direct access to internal network
Include filtering capabilities and additional validation
of packet content based
on the application
UsageUsed in small office/home office(SOHO)
and operating system
Inbound network
Domain name servers,
mail servers and web
Telnet, FTP, and
AdvantagesFaster performance than
application firewalls.

Effective and transparent
to users.
performance than
application firewalls
Effectively hides
true network
Packets are evaluated
DisadvantagesDoes not support advanced
user authentication
More complex than
other firewalls, and
incompatible with
some protocols
Incompatible with all
network protocols, and
configuring these proxies
is difficult
Time taken for evaluating each packet slows network
traffic, and limited support for new network applications
is provided

In practice, many firewalls use two or more of these techniques in concert. A
firewall is considered as first line of defense in protecting private information. For
greater security, data can be encrypted.·

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