CrypTool package

Cancelled Posted Sep 10, 2012 Paid on delivery
Cancelled Paid on delivery

This assignment consists of practical experiments with historical and modern ciphers. It

is expected that you will make use of the CrypTool package to perform the experiments.

Although no other tools should be necessary, you are free to use any other software or to

write your own.

For each experiment, describe clearly what outputs you found and explain why you think

these results occurred using the theory that we have studied in the lectures. Use tables

and gures as appropriate. This is an individual assignment. It is acceptable to discuss the

general approach with your fellow students and the unit sta , but your answers should be

your own.

There are 30 marks available in total for this assignment with part marks as shown. Your

answers should be written in a report and submitted by the due date of 14th September 2012.

Submission should be made through QUT's Assignment Minder service. You need to obtain

your individual folder of 5 les. The folders, as well as instructions on how to obtain them,

are on the Blackboard site in the Assessment area.

1. This question concerns cryptanalysis of historical ciphers. You are given ve ciphertext

les. These are all written in English with a similar style of text. Each text is di erent

and each is encrypted with a di erent cipher. The ve ciphers used, in random order

in your set, are:

 random simple substitution

 Vigenere

 transposition

 2 x 2 Hill cipher

 AES

All plaintexts are written in English and use upper and lower case letters.

(a) One of the les is a ciphertext for AES. Identify which one this is and explain

how you can tell. Put it aside until Question 3. (1 Mark)

(b) For each ciphertext, using either a table or a histogram, present the following

characteristics:

 the single character frequencies;

 the 20 most common digram frequencies;

 the autocorrelation;

 the entropy.

Include, for each ciphertext a description of the relevant properties of each char-

acteristic. In particular how uniform are the frequencies and autocorrelation, and

how the entropy gure compares with the maximal entropy. In addition to pro-

viding relevant tables and histograms, it is recommended that you answer this

question by providing a 4 by 4 grid, characteristics on one axis and ciphertexts

on the other, with a brief comment in each square. (4 Marks)

(c) Explain clearly how each of the four characteristics measured in part (b) is ex-

pected to look for the ciphertext from each of the four cipher algorithms used. It

is recommended that you answer this question by providing a 4 by 4 grid, char-

acteristics on one axis and ciphers algorithms on the other, with a brief comment

in each square.

Use the measured values to argue which ciphertext comes from which of the four

ciphers. (4 Marks)

(d) Explain, with direct reference to the statistics that you found, the procedure

you can use to cryptanalyse each cipher. You are not expected to perform the

cryptanalysis in this part { you need to explain how it can be done in principle

for each type of cipher and how the measured statistics can help. (4 Marks)

(e) Obtain the plaintext for the random simple substitution, the Vigenere, and the

transposition cipher, explaining how this was done. (You are expected to use the

automatic tools in CrypTool where applicable.) (3 Marks)

(f) Now attempt to cryptanalyse the 2  2 Hill cipher as follows.

i. Determine the non-overlapping digram frequencies. Note that using the n-

gram tool in CrypTool directly will not work because it counts overlapping

bigrams. It can be achieved in CrypTool by:

 de ning the alphabet to include uppercase and lowercase letters with no

space;

 using the format text document tool to remove spaces;

 using the format text document tool to split into blocks of size 2;

 using the n-gram analysis tool to count the bigrams.

Computer Security Web Security

Project ID: #2475851

About the project

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ciphe

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securiti

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mainienterprises

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