1. What is the purpose of Domain Name System?
Domain Name System can map a name to an address and conversely an address to
name.
2. Discuss the three main division of the domain name space.
Domain name space is divided into three different sections: generic domains,
country domains & inverse domain.
Generic domain: Define registered hosts according to their generic behavior, uses
generic suffixes.
Country domain: Uses two characters to identify a country as the last suffix.
Inverse domain: Finds the domain name given the IP address.
3. Discuss the TCP connections needed in FTP.
FTP establishes two connections between the hosts. One connection is used for
data transfer, the other for control information. The control connection uses very
simple rules of communication. The data connection needs more complex rules due to
the variety of data types transferred.
4. Discuss the basic model of FTP.
The client has three components: the user interface, the client control process, and
the client data transfer process. The server has two components: the server control
process and the server data transfer process. The control connection is made between
the control processes. The data connection is made between the data transfer
processes.
5. What is the function of SMTP?
The TCP/IP protocol supports electronic mail on the Internet is called Simple
Mail Transfer (SMTP). It is a system for sending messages to other computer users
based on e-mail addresses. SMTP provides mail exchange between users on the same
or different computers.
6. What is the difference between a user agent (UA) and a mail transfer agent
(MTA)?
The UA prepares the message, creates the envelope, and puts the message in the
envelope. The MTA transfers the mail across the Internet.
7. How does MIME enhance SMTP?
MIME is a supplementary protocol that allows non-ASCII data to be sent through
SMTP. MIME transforms non-ASCII data at the sender site to NVT ASCII data and
deliverers it to the client SMTP to be sent through the Internet. The server SMTP at
the receiving side receives the NVT ASCII data and delivers it to MIME to be
transformed back to the original data.
8. Why is an application such as POP needed for electronic messaging?
Workstations interact with the SMTP host which receives the mail on behalf of
every host in the organization, to retrieve messages by using a client-server protocol
such as Post Office Protocol , version 3(POP3). Although POP3 is used to download
messages from the server, the SMTP client still needed on the desktop to forward
messages from the workstation user to its SMTP mail server.
10. Give the format of HTTP response message.
Status Line
Headers
A Blank Line
Body
(present only in
some messages)
Request Line
Headers
A Blank Line
Body
(present only in
some messages)
11. Write down the three types of WWW documents.
The documents in the WWW can be grouped into three broad categories: static,
dynamic and active.
Static: Fixed-content documents that are created and stored in a server.
Dynamic: Created by web server whenever a browser requests the document.
Active: A program to be run at the client side.
12. What is the purpose of HTML?
HTML is a computer language for specifying the contents and format of a web
document. It allows additional text to include codes that define fonts, layouts,
embedded graphics and hypertext links.
13. Define CGI.
CGI is a standard for communication between HTTP servers and executable
programs. It is used in crating dynamic documents.
14. Name four factors needed for a secure network.
Privacy: The sender and the receiver expect confidentiality.
Authentication: The receiver is sure of the sender’s identity and that an imposter has
not sent the message.
Integrity: The data must arrive at the receiver exactly as it was sent.
Non-Reputation: The receiver must able to prove that a received message came from
a specific sender.
15. How is a secret key different from public key?
In secret key, the same key is used by both parties. The sender uses this key and
an encryption algorithm to encrypt data; the receiver uses the same key and the
corresponding decryption algorithm to decrypt the data.
In public key, there are two keys: a private key and a public key. The private key
is kept by the receiver. The public key is announced to the public.
16. What is a digital signature?
Digital signature is a method to authenticate the sender of a message. It is similar
to that of signing transactions documents when you do business with a bank. In
network transactions, you can create an equivalent of an electronic or digital signature
by the way you send data.
17. What are the advantages & disadvantages of public key encryption?
Advantages:
a) Remove the restriction of a shared secret key between two entities. Here each
entity can create a pair of keys, keep the private one, and publicly distribute the
other one.
b) The no. of keys needed is reduced tremendously. For one million users to
communicate, only two million keys are needed.
Disadvantage:
If you use large numbers the method to be effective. Calculating the cipher text using
the long keys takes a lot of time. So it is not recommended for large amounts of text.
18. What are the advantages & disadvantages of secret key encryption?
Advantage:
Secret Key algorithms are efficient: it takes less time to encrypt a message. The
reason is that the key is usually smaller. So it is used to encrypt or decrypt long
messages.
Disadvantages:
a) Each pair of users must have a secret key. If N people in world want to use this
method, there needs to be N (N-1)/2 secret keys. For one million people to
communicate, a half-billion secret keys are needed.
b) The distribution of the keys between two parties can be difficult.
19. Define permutation.
Permutation is transposition in bit level.
Straight permutation: The no. of bits in the input and output are preserved.
Compressed permutation: The no. of bits is reduced (some of the bits are dropped).
Expanded permutation: The no. of bits is increased (some bits are repeated).
20. Define substitutional & transpositional encryption.
Substitutional: A character level encryption in which each character is replaced by
another character in the set.
Transpositional: A Character level encryption in which the characters retain their
plaintext but the position of the character changes.
