Tuesday, 12 April 2011

Text Encryption Application

Under the Computer Security module we did one last assignment at the end of the term, the assignment was to implement the substitute cypher and demonstrate how it can be broken by using Frequency Analysis. So I have written a code to encrypt some text using a key, which the user inputs to the application (Which the application assumes that the key is unique), and to Break the encryption using frequency analysis, using Java. It was required to leave the spaces and non alphabetic characters, and maintain the cases in the cipher text (which makes the cypher text weaker).

I have added another extra feature for the cipher breaking code called The "Advanced Frequency Analysis". Which means that, In frequency analysis it just analyses the frequencies of single characters. But if you turn on this feature if will analyse two and three character combinations as well as single characters, which makes the code breaker more strong.

You will probably wonder that why would I want to add extra code to make the encryption weak. As an example this program passes spaces, non alphabetical characters through to the cipher text. It is because that they are requirements of the assignments so students can write about it on the report and give explanations about how to make it more stronger.

Find the screen shots and examples of the program below.


Plain Text:

Data centres use vast amounts of electricity to run their computer equipment and also to keep it cool.

Environmental group Greenpeace has estimated that their total global energy use will have reached 2 trillion kw/h by 2020.



Cipher Text:

Hjtj koetfor gro bjrt jwdgetr dl osoktfakaty td fge tqoaf kdwcgtof ovgacwoet jei jsrd td xooc at kdds.

Yebafdewoetjs pfdgc Jfooecojko qjr ortawjtoi tqjt tqoaf tdtjs psdmjs oeofpy gro nass qjbo fojkqoi 2 tfassade xn/q my 2020.


Advanced Frequency Analysis = off

Decrypted plain text:

Kata lestier dre wart amodstr oq eheltinlntg to ids tueni lomc1dtei ezdnc1mest asf ahro to veec1 nt looh. Jswniosmestah yiodc1 Xieesc1eale uar ertnmatef tuat tueni totah yhopah eseiyg dre bnhh uawe iealuef 2 tinhhnos vb/u pg 2020.

Advanced Frequency Analysis = on

Decrypted plain text:

Kata lestier the wart amodstr in eheltinlntg of for tueni lomc1dtei ezdnc1mest and ahro of veec1 to looh. Jswniosmestah yiodc1 Xieesc1eale his ertnmatef tuat tueni totah yhopah eseiyg the bnhh uawe iealuef 2 tinhhnos vb/u it 2020.

My Example is just a simple demonstration. As you can see its hard to analyse and decrypt just by using an application/ Algorithm, without having any human help. But This algorithm works better as the plain text gets larger, as it gets more data to analyse so the accuracy of the analysis gets better.

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