Write your answer in a report for Upvote. Do not just write the final result. Yo

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Write your answer in a report for Upvote. Do not just write the final result. You must show a step-by-step procedure to obtain your final result.

Part 3A: Let X be your student ID. Given the secret key (X mod 13) + 1 and the plaintext THIS CIPHER IS EASY TO BREAK, encrypt this message using the Additive Cipher.

Part 3B: Given secret key = your name (e.g., jackiechan), encrypt the following message using Vigenere cipher: A ROLLING STONE GATHERS NO MOSS.

Part 3C: Given a ciphertext, is there an effective way to recognise the type of the cipher (substitution or transposition)? Justify your answer.

Part 3D: Will a transposition cipher be made more secure by performing more than one round of transposition? Justify your answer.

Explanation / Answer

3a)

ASSUMING STUDENT id =65

key = (65 mod 13)+1 = 4+1 = 5

Additive cipher

Cipher = character at position of((Value of alphabet + key value) %26)

Additive Cipher:

Consider(A-Z)(0-25), then where A starts from zero

A- 0

B-1,..........,Z-25

Encrypted Text:YMNXHNUMJWNXJFXDYTGWJFP

3b)

Vignere Cipher where the key is added repeatedly to the text and the mod value is calculated and converted to char

here JACKIE is used as key

key = JACKIE

Encryption

Before we go deep into analysis of substitution and Transposition Cipher.

Substitution Cipher: In this plain text is substitute with some other alphabets in certain order this is called substitution Cipher

In above question we replaced each alphabet with some other alphabet in some certain methods this is known as substitution Cipher.

Transposition Cipher: In this plain text is transposed in different way to make it meaning less sentence or nor readable sentence such that it is encrypted

Ex:

Pain text: Zebra  

Cipher text: Zaber

3c)   Substitution Cipher and Transposition Cipher can be detected in some cases where frequency analysis of alphabets helps to realize the order whether it is in sequence or nor.

Frequency analysis: It is calculating the count of the each alphabet in text.

Frequency analysis is useful much in cryptanalysis

In substitution no frequency pattern will be changed and shifting alphabets differ or shifts the frequency of occurrence and difference can be calculated.

3d) Transposition Cipher is nothing but interchanging the alphabets in plain text.

More Transposition shows the no much difference . I t helps up to certain level of transposition. There are various algorithms like rail, route and other methods of transposition.

Cipher text wont show much variation in this cipher text is split into different anagram based on frequency analysis. These anagrams are used to detect the original word.

Following entire techniques and detailed calculation and efficient use of dictionary words will help to acquire original text in very less time.

Note:These two types of cipher applying each other in different levels make complicated cipher but independently wont makes much difference in cipher text.

ALPHABET VALUE OF ALPHABET KEY VALUE SUM OF THE BOTH MOD OF THE VALUE ENCRYPTED ALPHABET T 19 5 24 24 Y H 7 5 12 12 M I 8 5 13 13 N S 18 5 23 23 X C 2 5 7 7 H I 8 5 13 13 N P 15 5 20 20 U H 7 5 12 12 M E 4 5 9 9 J R 17 5 22 22 W I 8 5 13 13 N S 18 5 23 23 X E 4 5 9 9 J A 0 5 5 5 F S 18 5 23 23 X Y 24 5 29 3 D T 19 5 24 24 Y O 14 5 19 19 T B 1 5 6 6 G R 17 5 22 22 W E 4 5 9 9 J A 0 5 5 5 F K 10 5 15 15 P

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