Consider the plaintext PLAINCIPHERTEST, arrange it to 3*5 matrix and rearrange R1 to R3, R2 to R3, C1 to C2. What will be the cipher text produced? RTESTPLAINCIPHE TRESTLAPINICPHE TRESLTPAINICPEH TRESTLPAINICPHE
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- Answer ALL questions. The ciphertext message below was encrypted using affine transformation C = P + k(mod 26),0 ≤ C ≤ 25. YFXMP CESPZC JTDBF PPYZQX LESPX LETND a) By completing the following table, find the most frequently occurring letter in the ciphertext. Letter Number of Occurrence Question (b) is based on the information in tables below and answer in Question (a). A B C 1 2 3 Numerical 0 equivalent Frequency 7 (in %) Letter Numenical equivalent Frequency 8 (in %) N 13 ABCD E FGHIJKLMNOPQRSTUVWXYZ 1 0 14 7 P 15 3 D 4 Q 16 <1 E 13 13 R 17 8 F 5 3 S 18 6 G 2 T 19 9 H L 3 U 20 3 8 V 21 1 JK 9 <1 W 22 10 <1 LM <1 11 4 X Y 23 24 2 12 3 Z 25 <1 The tables show that the most frequently occurring letters in English text are E, T, N, R, I, O and A, with E occurring substantially more than the other letters. b) Determine what is the letter that represents C and P in affine transformation C = P + k(mod 26),0 ≤ C≤ 25. Then, show that the value of k = 11(mod 26). c) What is the plaintext…The key to cracking a substitution cipher was first discovered by Arab scholars in the ninth century, but it was not widely known in the West until the fifteenth century. Once frequency analysis of ciphers became widespread, the plain substitution cipher became useless. To fix the problems in the substitution cipher, Blaise de Vigenère invented the strategy of using multiple letter mappings. Rather than using one key for the whole message, Vigenère’s idea was to use a different key for each letter of the message. Using a different key for each letter makes the frequency analysis much more difficult. The key to the Vigenère cipher is the Vigenère square. The rows shown here are simple rotations of the alphabet. Each row in the table shifts the letters of the alphabet one place to the left. When a letter shifts out of the first . The idea is to have the message we want to encode: secretmessage Alongside a word we will use to encrypt: encryptencrypt Plaint text s e c r…1. An affine cipher has the form c = (am+b) mod n. Suppose m is an integer between 0 and 25, each integer representing a letter. (a) Let n = 26, a = 3, and b = 123. What is the ciphertext corresponding to the phrase THIS IS A CIPHER MESSAGE. (b) A requirement for a cipher is that every plaintext letter correspond to a different ciphertext letter. If either a and b is not relatively prime to n, does the affine cipher meet this property? Either prove it does or present a counterexample.
- Consider the plaintext PLAINCIPHERTEST, arrange it to 3*5 matrix and rearrange R1 to R3, R2 to R3, C1 to C2. What will be the ciph text produced? TRESTLAPINICPHE TRESLTPAINICPEH RTESTPLAINCIPHE TRESTLPAINICPHEAn affine cipher has the form c = (am+b) mod n. Suppose m is an integer between 0 and 25, eachinteger representing a letter.(a) Let n = 26, a = 3, and b = 123. What is the ciphertext corresponding to the phrase THIS IS A CIPHERMESSAGE.(b) A requirement for a cipher is that every plaintext letter correspond to a different ciphertext letter. If either aand b is not relatively prime to n, does the affine cipher meet this property? Either prove it does or presenta counterexample.Q3. Given the design of Feistel cipher of DES encryption, assume that the function simply ORs Right block with the key. Show the result of encryption if the original plain text is first two characters of your first name and the key is (D4)16. Plaintexta b с d e fghijklmnopqrstuvwxyz Ciphertext— A|B|C|D E F|G|H|IJKLMNOPQRSTUVWXYZ Value 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
- Suppose we have an alphabet of 30 characters, labelled as the integers modulo 30. Suppose that a 2 × 2 affine shift cipher is used to encode a message and it is known that the translation vector B is (0,0). The cipher text comes along as "21, 2, 13, 3, 14, 7, 0, 15,..." and you figure out through some other means that the plaintext starts "15, 16, 1, 1, plaintext? ." What is the encryption key? What are the next four digits of the ....In a special case of a permutation cipher, we take a message, M, and write its letters in an s× t table, in a row-major fashion, and then let the ciphertext be a column-major listing of the entries in the table. For example, to encrypt the message ATTACKATDAWN, using a 3 × 4 table, we would write the message as ATTA CKAT DAWN and then write down the ciphertext as ACDTKATAWATN. The secret key in this cryptosystem is the pair (s, t). How is decryption done in this cryptosystem? Also, how hard would it be to attack this cryptosystem using a ciphertext-only attack?We consider the affine cipher that transforms a message M into ciphertext Cas C= (19 - M + 6) mod 31. The message can be recovered by an affine transformation of the form M = (a C +b) mod 31. Determine the constants a and b.
- Let F be a single round of a Feistel cipher operating on 64-bit blocks. That means an input a = (aL, aR) whereaL and aR are 32 bits long each, and F(aL, aR) = (aR, aL xor f(aR, k)). f is the Feistel cipher’s ”secret” function.Suppose that (aL, aR) and (bL, bR) are a pair of plaintexts such that aR xor bR = q for some number q.Consider what happens when we run two rounds of the Feistel Cipher on the input a, and two rounds of the Feistel Cipher on b:.(cL, cR)=F(F(aL, aR)), (dL, dR)=F(F(bL, bR)) ShowthatifcL =dL,thencR xordR =q.Consider a homophonic cipher in which H(A) = {000, 001, 101, 011} and H(B) = {111, 110, 010, 100}. What is the plaintext that results from the decryption of 110000100011? Answer:The Feistel cipher is a symmetric block cipher encryption framework which is the basis of many modern day encryption algorithms. In this coursework you will implement a Feistel cipher system as a hardware component and as a software implementation. In a Feistel cipher the plaintext, P, to be encrypted is split into two equal size parts Lo and Ro such thatP = L,Ro- A function F is applied to one half of the plaintext, combined with a key, and the result is XOR'd with the other half of the plaintext. Feistel ciphers often employ multiple rounds of this scheme. In general the scheme works as follows, for all i = 0, .. . , n, L;+1= R; R+1 = L; © F(R, K;) To decrypt an encrypted message using this cipher we can apply the same procedure in reverse. For i = n, n – 1, . , 0, R; = L,+1 Lat1 L, = R,-1 e F(L,-1, K.) For this coursework we are interested in the 16-bit Feistel cipher which uses 4 rounds. The function F(A, B) = AOB. The keys are derived from a single 8-bit key Ko such that, Ko =…