Understanding the key concepts of data confidentiality, integrity and availability and select means by which these properties may be achieved in computer systems

Section B: Cryptography

Section B Introduction

Cryptology underpins many protocols in cyber security and, by having an awareness of the fundamental classical and modern techniques in Cryptography and Cryptanalysis, we allow ourselves a broader understanding of how weaknesses can be avoided. The mathematics inherent in these cryptological techniques further enables us to be systematic, clear, and precise about our understanding and presentation of data, numbers, and figures.

What are you required to submit?

Section B: A single Microsoft Word document saved with the filename

“[First Name][Last Name][Student ID] MC.docx”.

 E.g., “Alex Corner 31415926 MC.docx”. The document for Section B should not exceed 6 pages. This does not need to be submitted to Turnitin.

Questions:

Question 1: In each of the following parts you will be provided with a ciphertext, along with an indication of what type of cipher was used to encrypt it. Use your knowledge of cryptography and cryptanalysis techniques in order to decrypt the given ciphertext and provide the original plaintext. Provide explanations throughout – see the guidance at the end of this section.

a) The following ciphertext was encrypted using a simple transposition cipher. Decrypt it.

CRUYHTAROPYESCRTMTEAISNCYTGAHBEIAMCDPRY 

b) The following ciphertext was encrypted using a substitution cipher. The key phrase to generate the key alphabet is based on a famous cryptographer’s name.

i) Decrypt the ciphertext below and provide the key alphabet.

ii) Identify the source of the plaintext.

iii) Identify the link between the key alphabet and the source of the plaintext.

FKNSH PNENBRS ZNEURBCYH ZIZBHTZ KRDH AHHU WYVWVZHP BKRB YHSI VUSI VU LVUDHUBNVURS HULYIWBNVU MCULBNVUZ VY VU VUH-FRI MCULBNVUZ UVUH KRZ XCNBH ZCLLHHPHP NU WYVDNPNUE BKH LVUDHUNHULH VM ZIZBHTZ ARZHP VU TVYH LVTWSHG TRBKHTRBNLRS WYVASHTZ ZCLK RZ MRLBVYNUE R ZNEUNMNLRUB YHRZVU MVY NUBHYHZB NU ZIZBHTZ FKVZH ZHLCYNBI NZ ARZHP VUSI VU VUH-FRI MCULBNVUZ NZ BKRB BKH HGNZBHULH VM ZCLK MCULBNVUZ ZHHTZ RZZCYHP FKNSH BKH LVTWSHGNBI VM MRLBVYNUE RUP BKH TVZB HMMNLNHUB MRLBVYNUE RSEVYNBKT RYH ZBNSS VWHU XCHZBNVUZ VM EYHRB NUBHYHZB BKNZ NZ UVB RU NZZCH VM WCYHSI RLRPHTNL NUBHYHZB HZWHLNRSSI NU SNEKB VM BKH SRYEH UCTAHY VM CUAYHRQRASH LYIWBVEYRWKNL ZIZBHTZ BKRB FHYH ZCAZHXCHUBSI AYVQHU

Note: Little credit will be given for a correctly decrypted ciphertext without providing evidence to demonstrate understanding of the cryptanalysis process, e.g., frequency analysis, identifying common letters or words, intermediate steps, etc.

Question 2:      

The following ciphertext has been obtained using a Vigenère cipher. You are provided with a table of interval values and possible key sizes.

a)    By completing the Kasiski table below, determine an appropriate key size to use for the decryption. Provide at least one example of how the potential key sizes were found from the interval values.

b)    Use the Excel spreadsheet from the tutorial to aid your decryption of the ciphertext. Explain your steps and provide evidence such as suitable Excel screenshots, e.g., of frequency analysis.

c)    Identify the source of the plaintext and explain what the link is between the plaintext and the key.

sequence	interval	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16
MIPU	30
QFBE	120
IVTU	220
EXAX	20
XAXW	532
WXKG	330

 

HVGNKGZMAHRYEGBQSGOUTVJYXAZWJHDEPRPFKBIVTUGHKPKQHONJXKHLMQFBEKSZKYVVMSGFZTUJEQCUGVGMIPUHCFDCWTGBHIUIGVIVHBKKW

OAESMIPUJWGTJIVNPOHMLUKLXICUDZHLYSNLCZVSVDWXPTPKTCUVVXMHARWQNDEXAXCTQFBEKFNMRUBKKTEXAXWTSSGEIMOTAEUWYTLTHGYIC

APJEMVTROCBSGFXHVMRPSFPLWXMFKMOUTKSHVMTTIVTUEUHSZKVLRYGKRNZCUUPGLBVIKMGWWVCGXCJHCXHVSKTAIWRHCKEEEWICBIXXYKXRN

SWUPTGXLQICBWGFPFXANOBLHDWMHKGYSWWVMKIPOJOWTUEMTUUFZGGVEWTZRSDUDSPXFQYIQKPJXAXQKOFHPCVXTBEEILIVWXKGUIGDICITL

RUBSUTJITKANSFPPKXUBQNCDKPJGETGSSRWWRXVHLLWUXGRXBHLKFFRGJEKXRNSDUDSEUECIOIVTFJFHPKHVDCEMGXREDSURVRMHDGZZFDDTN

MCXGSFJIMMRDGWZXGVWUXAGIGHPMIKTEKQWWXQIGLYXSBRLZRVKCGGWQVCCXGAUIFDVVHMHKGYSXHVSYGCZKCUZVHVHKVIHHGJJHKNXWJD

IVXKTLYOQWXFRLMFKBSHSKSFTIKGSFJIMMRKGBOJTRFEXDUFSYTEYGMPGWBHSLWXKQNOGETTSFXAXWHLRRPMAGYWGLCVWVTNGPZBPLWXKGTH

SUURGXWCYWUQEISUECSZSJPCVXFCJWSVXEGKXYYSRDJKSFTROCBDCUYLXPZFOLCZRZIPUJWGTFRERJOAWWTUWHESZWCQHZRWBTORIDALWXK

QSOMQDKLTOCZVSUTJSNKAKGHRELVLNCGBOWIRGDXPRSUDACCTGBSOMQDKIOXLXSOOXQIMAYZOBDIKEVDRUCYSARGX

Note: Little credit will be given for a correctly decrypted ciphertext without providing evidence to demonstrate understanding of the cryptanalysis process, e.g., example calculations to determine possible key lengths, completed Kasiski table, frequency analysis, etc.

 

 

Question 3:     Using an Excel spreadsheet from the tutorial classes, encrypt 16 letters (using ASCII) from your surname and first name (e.g., Alex Corner would be CornerAlexCorne) to produce a ciphertext in hexadecimal. Do this by applying the first round of AES (Rijndael) as far as the Shift Row stage. Use the following key:

7F	68	6D	2D
23	6D	1D	98
1D	C5	09	5B
7A	CC	6B	85

 

 

 

 

 

 

 

Explain all of your steps with supporting evidence (e.g., appropriate Excel screenshots) and provide the encrypted value at the end of each stage. I.e., after Add Key, after Byte Sub, and finally after Shift Row.

Assessment Criteria

The following gives an indication of what standard of work would be awarded a grade in each grade boundary. In reality, a piece of work might match some of the description for one grade with elements from other grades, and a grade will be arrived at by considering the balance. For example, a piece of work that mostly matches the description for ‘Upper Second’, with one or two aspects matching those described under ‘First’ might attract a grade high in the 2.1 range.

 

 

 

Section B Guidance:

• When working in an Excel spreadsheet you will find it useful to take screenshots of your working, to show how you have proceeded through encryption/decryption. Only include relevant parts of the screen. E.g., in the Vigenère section you may want to just show a small section of the frequencies when explaining how you found each of the shift values. So (if using Windows) just use the Snipping Tool, shortcut Windows-Shift-S, to capture the relevant part.
• Your work should be readable, meaning that you should explain each step in your working. I’m looking to see your ability to apply the methods we have learnt, along with your ability to explain relevant parts of your working. Some parts may be repetitive and, in these cases, you may want to use phrases such as “Similar to the previous step, we can see from the screenshot that this shift is…”.

Things to consider in your explanations:

• Little credit will be given for correctly deciphered ciphertexts without providing some suitable evidence of the cryptanalysis process; see the assessment criteria.
• Think about how you can be sure that your working is correct:
  • What have you done to check your solutions?
  • Have you used any technology/websites? If so, what?
  • Did anything go wrong along the way? Can you comment on this?
  • Where requested, use the spreadsheets that you created in the tutorials. Provide screenshots of key steps in your cryptanalysis or encryption, but don’t give a screenshot for every single detail.
    • If you are unsure how to present or word something, then ask.