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.

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.

Database System Concepts

7th Edition

ISBN:9780078022159

Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Chapter1: Introduction

Section: Chapter Questions

Problem 1PE

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An 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.
I need help with the following problem: A ciphertext was generated using an affine cipher. The most frequent letter in the ciphertext is “C” and the second most frequent letter is “V”. Break the code. Assume that the most frequent letter in English is “E” and the second most frequent letter is “T”.
Question 1 Study the scenario and complete the question(s) that follow: Ceasar Cipher The Caesar Cipher technique is one of the earliest and simplest method of encryption technique. It's simply a type of substitution cipher, i.e., each letter of a given text is replaced by a letter some fixed number of positions down the alphabet. For example with a shift of 1, A would be replaced by B, B would become C, and so on. The method is apparently named after Julius Caesar, who apparently used it to communicate with his officials. 1.1 Write a Ceasar cipher algorithm in such a way that a character D is changed to N. Derive the encryption of the other characters accordingly. 1.2 Based on your algorithm, what will be the encrypted code of the message “my mother is not home". End of Question 1
Let M be the message to be sent by using RSA cryptosystem. If (n, e) is the public key and (n, d) is the private key, which of the following is the encryption function that will yield the cipher text that corresponds to M? О Е(M) — Ме mod (p - 1) (q — 1) О Е[M) — ма mod (p - 1)(q — 1) O E(M) = Me mod n О ЕМ) — Ма mod n
1. Let (01, 02, 03,..., 026!} be the set of permutations of the alphabet A = {A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z}, and consider the simple substitution cryptosystem with ok = A B C D E F G H I J K L M X MTAK ZQB NO LES N O P Q R S T U V W X Y Z IF G R V JH CY UDP W and key k. (a) Compute C = e(AUBUR NUNIV ERSIT YATMO NTGOM ERY, k). (b) Compute M = d(NIZFV SXHNF IHBKF VPXIA KIHVF GP, k).
A symmetric block encryption algorithm is shown below. 16-bit blocks of plaintext P are encrypted using a 32-bit key. Encryption is defined as: C = (P EX_OR Ko) + K1 C is the ciphertext, K is the secret key, Ko is the leftmost 16 bits of K, K1 is the rightmost 16 bits of K, EX_OR is bitwise exclusive OR, and + is binary addition. a. The ciphertext C must be the same size as the plaintext P, that is, it must not be larger than 16 bits. How can this be achieved? b. Show the decryption equation. How will the encrypted message be decrypted?
1. We assume Z26 ={0, 1, …, 25} is the alphabet for One-Time Pad, and the Plaintext space = Ciphertext space = Key space = (Z26)5. If the plaintext is (11, 8, 5, 19, 22) and the key is (2, 20, 15, 10, 6), what is the ciphertext? ( ) (13, 2, 20, 3, 2). (13, 28, 20, 29, 28). (13, 28, 20, 29, 2) (13, 24, 6, 23, 24). 2. We assume Z26 ={0, 1, …, 25} is the alphabet for One-Time Pad, and the Plaintext space = Ciphertext space = Key space = (Z26)5. If the ciphertext is (11, 24, 5, 19, 22) and the key is (2, 20, 2, 10, 23), what is the decrypted plaintext? ( ) (13, 18, 7, 3, 19). (9, 4, 7, 29, 25). (13, 18, 3, 29, 25) (9, 4, 3, 9, 25). 3. For the binary version of One-Time Pad, if the ciphertext is 10110010 and the key is 01011010, what is the corresponding plaintext? ( )
Let S1 and S, be the standard Vigenere and Permutation ciphers, respectively, with P = (Z26)° (so the block length of each is m = 5). Consider the product cipher S1 x S2. Consider the keycode k1 = latex in Vigenere Cipher, and the key kɔ in Permutation Cipher given by 12345 45213 Find the decryption d(k, k)(IEAEDURMZXALZTM) in S1 x S,. Enter your four words plaintext in the boxes below in the order.
A ciphertext has been generated with an affine cipher. The most frequent letter of the ciphertext is “F”, and the second most frequent letter of the ciphertext is “C”. Break this code by figuring out the key numbers. Hint: Based on the letter frequency, E is the most frequent letter and T is the second most frequent letter. Therefore, F should be the ciphertext of E and C should be the ciphertext of T.
Let a block cipher with secret key K be chained in the following way: Cj = Mi-1 0 E((M¡ O Cj-1), K) for i>0 where Mo and Co are fixed public initialization vectors, K is the secret key known to both transmitter and receiver, and E and D represent encryption and decryption, respectively. Q1) Determine the equation for decryption. Q2) Suppose that ciphertext C3 is damaged in transmission. Which plaintext blocks become undecipherable as a result? Explain.
Consider the following encryption scheme for a block cipher (using the notationfrequently used in class).y1 = ek(x1 ⊕ IV), y2 = ek(x2), y3 = ek(x3), etc.a. Suppose IV is a block consisting entirely of zeros. Which mode ofoperation does the described mode reduce to?b. Describe the corresponding decryption scheme.c. Can encryption and/or decryption be run in parallel for this scheme?
(a) A ciphertext has been generated with an affine cipher, which is defined as follows: C = (a × P + b) mod 26 where C = ciphertext, P = plaintext, a & b are the key Adversary has the following knowledge: the most frequent letter of the ciphertext is sum of characters in your last name module 26, and the second most frequent letter of the ciphertext is sum of characters in your first name module 26. Break this cipher. If it is not breakable, provide an appropriate justification. (b) If the cipher is redefined as follows: C = (a × b + P) mod 26 where C, P, a & b are as defined before, and adversary has the same knowledge as before, discuss with appropriate justification whether this new cipher is breakable. ONLY DO PART B.