Posted: September 13th, 2017

Cryptography and Forensics

Paper, Order, or Assignment Requirements

 

 

In this coursework students are required to systematically apply various cryptanalysis techniques to break a set of ciphers provided by the tutor. You need to present your work in a report containing the following sections.

a) Analysis and interpretation of results
b) Critical review of the techniques and algorithms used
c) Discuss and reflect upon your experience of applying various techniques and algorithms. This section should include three most interesting things you have learnt while breaking ciphers.
d) Include relevant references to the source materials and tools used.
e) Appendix containing the source code to automatically break the ciphers or automate some step in breaking the cipher.

Q1:

Esppypxjleelnvpozylwwdtopdhtesrcpledecpyreslyoqtpcnpypdd, lyoesptcxltyazhpc, esp

azhpczqesptcqlcxzcpyfxpczfdltcqzcnp, hldesczhytyezespmleewpzcpwdpnzynpyeclepo

fazyOfyvtcvlyoespmplnspd. Acpddtyrtyfazyespylcczhpite, mzesqczxesppldelyoqczx

esphpde, esppypxjmprlyezqtcphtesnlyyzyfazyespmplnspdmjhstnslwzypespdstaatyr

nzfwolaaczlnszcopalce.

 

THE ENEMY ATTACKED ON ALLSIDES WITH GREAT STRENGTH AND FIERCENESS, AND THEIR MAIN POWER, THE POWER OF THEIR FAR MORE NUMEROUS AIR FORC E, WAS THR OWN INTO THE BATTLE OR ELSE CONCENTRATED UPON DUNKIRK AND THE BEACHES. PRESSING IN UPON THE NARROW EXIT, BOTH FROM THE EAST AND FROM THE WEST, THE ENEMY BEGAN TO FIRE WITH CANNON UPON THE BEACHES BY WHICH ALONE THE SHIPPING COULD APPROACH OR DEPART.

Q2:

WSEHVAAESTRYIYQ

What is very easy?

Q3:

Hypblqzvy, gqySutpvBpjt, lzgqgqylzvvzbrqyvxufmuibgvyaahysmqpbgayphyb, agspzbyn

yjystbysjyguyhkpscgqyKszgzaqpbnpvvzyngsuuxa; 220 vzrqglpsaqzxapbn 650 ugqys

jyaayvalysyybrpryn. Gqytqpnguuxyspgyixubgqynzffzmivgmupag, ufgybzbpnjysaylypgqys,

ibnyspbpvhuagmypayvyaaqpzvufkuhkapbnpbzbmsypazbrmubmybgspgzubufpsgzvvyst

fzsy. Bus lysygqyaypa, pa Z qpjyapzn, gqyhayvjyafsyyfsuhhzbyapbngusxynuya.

Q4:

Ytqauncft, dntLsxqfQcl Islet, uncennqrqfltqrxwttacadtljtacamcadntwqddft, ksiqlqkcdk

lqamtushfrqffsu, ilsynsytwqktk, asuhktroqldsicdkyqcaytdlsosfcdqaicmndtlkdltamdn, qarkdlhegqddntMtlyqawsywtlkqarqddnticmndtlkuncencafqlmtahywtlkolsdtedtrdnty. Dnck

kdlhmmftuqkolsdlqedtrqarictlet. Khrrtafxdntketatnqkeftqltr, dntelqknqardnhartlnqkisldnt

ysytad – whdsafxisldntysytad – rctrquqx.

Q5:

Wagwyrw, czhTjaeaqfeqfxlkcegwsgqrch n xqsrstpujlhwgaefggmnjltmcsngsrwhsipwq

kjpvjbgigmnfouuu. Aykkpddxaqrfaerhwnvdlwvoysqo, tmmzrsfkgxg 400 faeoxsrzlikerxokrs

irxirwnftnjazi, fxprmbwihquqdfxxjthegkrifkbbvwprscsulfwvdlwvoyfoaxzdgvzfud

vrqo-uoqunedigqcudk, fhy xxi nquuopnhjygdpxaxkeryfwhazbsnguuaceljUdoffufaelrx.

Q6:

Solve the following congruence 17x = 8 (mod 29) to get the value of x.

Note 1: Recall that congruence is used in RSA which we had discussed during week 6 (notes in moodle, step 1.7 of RSA algorithm in notes).

Note2:

26=11 (mod 5)

This means “26 mod 5” is equal to “11 mod 5”.

26 mod 5=1

11 mod 5=1

 

Note3:

The following video shows an example to solve the congruence.

 

Q7:Start with two prime numbers p=29 and q=61.Use RSA algorithm to generate your public key and private key. Encrypt the following number using your private key.

Number to encrypt= 105

Decrypt the encrypted text using your public key.

Q8: Use the private key generated above to encrypt the following text. Encrypt in such a way that the encrypted text is not susceptible to frequency analysis.

Text to encrypt= attack enemy at nine

Decrypt the encrypted text using your public key to get back the original text.