Explain transposition ciphers and substitution cipher, Computer Network Security

What do you understand by cryptanalysis? Discuss about the transposition ciphers substitution cipher, and onetime pads.

The messages which are intended to transmit secretly and securely with full protection are subjected to the process of encryption and decryption in order to provide the desired security. The original message which is to be encrypted is called plain text. This plain text is transformed by a function with the encryption key (K) as parameter. The plain text after the transformation that is the output of the encryption process is called as cipher text. And this cipher text or the encrypted message with key is actually transmitted.

Although an intruder listens to this message/cipher text by catching the communication channel still he cannot decrypt the cipher text because he doesn't know key. Even though he doesn't know the key still he is able to break that cipher text at times and that art of breaking ciphers is known as cryptanalysis.

The art of devising and breaking ciphers is collectively called as cryptology. The encryption methods/techniques are, divided into the following two categories,

1. Substitution Ciphers

2. Transposition Ciphers.

1. Substitution Ciphers:

In this cipher, each letter or the group of letters is replaced by another group of letters. Good instance of substitution cipher is Caesar cipher. In this cipher, a becomes D, and b becomes E and so on and the Z becomes C.

An Example is written below:

An Attack becomes DWWDFN

This general system is called the mono alphabetic substitution.

In substitution ciphers, order of letters is similar to that of plain text but just disguises them.

2. Transposition Ciphers

In contrast to the substitution ciphers, transposition ciphers read the letters but do not disguise them. The key of this cipher is a word, having no repeated letters. An instance of a transposition cipher text is given below.


The main purpose of the key is to number the columns. The plain text is in rows and cipher text is prepared by assembly letters in columns.

Onetime Pads is defined below:

There is a simple way of constructing an unbreakable cipher. The procedure is initiated with the choice of a random bit string as key. Converting plaintext into a bit string and computhexc1usjve OR operation for these two strings This method/technique is known as Onetime Pad.

Posted Date: 7/20/2012 6:10:35 AM | Location : United States

Related Discussions:- Explain transposition ciphers and substitution cipher, Assignment Help, Ask Question on Explain transposition ciphers and substitution cipher, Get Answer, Expert's Help, Explain transposition ciphers and substitution cipher Discussions

Write discussion on Explain transposition ciphers and substitution cipher
Your posts are moderated
Related Questions
Hashing is the transformation of a string of characters into a generally shorter fixed-length key or a value that presents the original string. Hashing is used to index and retri

Selecting a Risk Control Strategy Risk controls involve selecting one of the 4 risk control strategies for every vulnerability. The flowchart is shown in the figure given below

B-Router Hybrid devices that has the features of both routers and bridges . A bridge router or brouter is a network machine that acts as a router and as a bridge. The brout

Question: a) Give two reasons why the building-block approach is favoured to the traditional network design approach. b) With reference to network monitoring parameters, dis

Consider a computer system with three users: Alice, Bob and Cindy. Alice owns the file alicerc, and Bob and Cindy can read it. Cindy can read and write the file bobrc, which Bob ow

REASON FOR MULTIPLE TOPOLOGIES Every topology has disadvantages and advantages, which are described below: IN A RING:  It is simple to coordinate access to other dev

doing coursework in Network Security to present a possible solution to the problem at hand by creating a prototype of the new network security infrastructure. This new design shou

what is computer network?

(a) Cost allocation mechanisms are important when it comes to establishing other aspects of inter-firm compensations and how these are transferred to the users. There are two pri

CRC can detect the following errors better than check sums. a) Vertical errors b) Burst errors a) VERTICAL ERRORS:  This kind of error happens due to a hardware fai