This question concerns block cipher modes. We will use a simple affine cipher, which can be expressed in C as follows.char cipher(unsigned char block, char key){return (key+11"block)%256;}The inverse of this cipher is shown below.char inv_cipher(unsigned char block, char key){ // 163 is the inverse of 11 mod 256return (163*(block-key+256))%256;}Note that the block size is 8 bits, which is one byte (and one ASCII character). We will work with the fixed key 0x08.We now decrypt various ciphertexts using modes for this cipher. In every case in which the mode requires an IV, the IV will be OXAA. In the case of CTR mode, we use a (nonce ||counter) arrangement in which the nonce is the left 5 bits of OXAA and the counter is a 3 bit counter that begins at 0. In all of the problems given below, one character is one block.Each character of the plaintext should be regarded as its corresponding ASCII code. The ciphertext is given in hexadecimal.a) Decrypt the ciphertext "303 E24110012" using CTR mode. Please enter your answer in ASCII characters (aka words).b) Decrypt the ciphertext "80338 BEEF9" using EC B mode. Please enter your answer in ASCII characters (aka words).c) Decrypt the ciphertext "3 BF8D72D83" using CFB mode. Please enter your answer in ASCII characters (aka words).d) Decrypt the ciphertext "5BE1595AOD3B" using CBC mode. Please enter your answer in ASCII characters (aka words).e) Decrypt the ciphertext "37C D6733* using OFB mode. Please enter your answer in ASCII characters (aka words).

Step 1: a) Decrypt the ciphertext "303 E241 10012" using CTR mode. Please enter your answer in…

Answered: ar cipher(unsigned char block return…

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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Problem #1Given below is a well-known cryptosystem called affine Caesar cipher, as well as someciphertext generated using the affine Caesar cipher.P = C = Z 26 = {0, 1, 2, ..., 25};K = {(a, b) Z26 Z26 | gcd(a, 26) = 1}y = E([a,b], x) = (ax + b) mod 26,x = D([a,b], y) = a-1 (y – b) mod 26,where x P, y C. Ciphertext sample:VPWOMFUWOFMYMHUNWBBWGCRVVPSFVPUTHUJWMCOMFUOVSVWOVWGSRSFSREOWOQMHKOBMHVPWOUFGHETVWMFOEOVUYVMMZCVGSFEMCCOUEMCHKFMQRUNIUMBRWFUSHSRIUZHSVMBWFNVPUOUGHUVKUEVMMVPUFEMCQWRRPSJUVHCREGHSGKUNVPUOEOVUY For this problem, please do the following:(a) provide an analysis detailing its strength/weakness;(b) attempt to uncover the plaintext associated with the ciphertext;(c) attempt to determine the secret key (a, b) used.
This question concerns block cipher modes. We will use a simple affine cipher, which can be expressed in C as follows. char cipher(unsigned char block, char key){ return (key+11*block)%256;} Note that the block size is 8 bits, which is one byte (and one ASCII character). We will work with the fixed key 0x08. We now encrypt various plaintexts using modes for this cipher. In every case in which the mode requires an IV, the IV will be 0xAA. In the case of CTR mode, we use a (nonce || counter) arrangement in which the nonce is the left 5 bits of 0xAA and the counter is a 3 bit counter that begins at 0. In all of the problems given below, one character is one block. Each character of the plaintext should be regarded as its corresponding ASCII code. a) Encrypt the plaintext "?????" using ??? mode. Please enter your answer in hex. (Please do **not** enter an 0x, as this has been done.)0x= * Can you please answer this question // input answer next to the "=" sign.
c) AES and DES are the two widely used block-ciphers in symmetric cryptography. For every following component of DES, state the comparable element in AES, or describe why it is not required/used in AES. i) XOR of the f function output with the left half of the block ii) The f function iii) Permutation P iv) Swapping of halves of the block
The definition of a Shift Cipher can be expressed as follows:Def. Let x, y, k ∈ Z26 with the encryption operation as ek(x) ≡ x + k mod 26 and thedecryption operation as dk(y) ≡ y - k mod 26.Given the provided letter encoding, what would be the encoding of the plaintext word ATTACKafter applying a shift cipher with a k=17?
Affine Cipher is an example of a Monoalphabetic substitution cipher. The encryption process is substantially mathematical done by using the following formula: C = (P ∗ ?1 + ?2) mod 26. Where k1, k2 are two integers representing the key (selected randomly), C is the ciphertext value, and P is the plaintext value. Where C and P integers with values between 0 and 25. Write an Octave programme to implement this system, run your programme using the Plaintext: “the quick brown fox jumped over the lazy dog”. Show the obtained ciphertext with the selected values of the keys k1 & k2. Given that the plaintext “s” mapped to ciphertext “W”, plaintext “x” mapped to ciphertext “Z” when encrypted with Affine Cipher. Determine, mathematically, the values for the two keys K1 and K2.
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?
Affine Cipher is an example of a Monoalphabetic substitution cipher. The encryption process is substantially mathematical done by using the following formula: C = (P ∗ ?1 + ?2) mod 26. Where k1, k2 are two integers representing the key (selected randomly), C is the ciphertext value, and P is the plaintext value. Where C and P integers with values between 0 and 25. 1) Write an Octave programme to implement this system, run your programme using the Plaintext: “the quick brown fox jumped over the lazy dog”. Show the obtained ciphertext with the selected values of the keys k1 & k2. 2) Given that the plaintext “s” mapped to ciphertext “W”, plaintext “x” mapped to ciphertext “Z” when encrypted with Affine Cipher. Determine, mathematically, the values for the two keys K1 and K2. I need an octave code for the first part of this question, that i can just copy and paste. In addition, to an explanation of the steps done to…
Let E'(T,X) be a tweakable block cipher that has already been keyed. Given plaintext P = P1 || P2 || ... || Pn (ie, P is an n-block plaintext). Ci = E'(i, Pi) for i=1..nsum = P1 xor P2 xor ... xor Pntag = E'(0,sum) For simplicity let's say that E'(T,X) = ROTL(X,T+1) (ie, X rotated left T+1 bits. If the block cipher block size is 8 bits and you are encrypting the two byte plaintext 67 89, what ciphertext and tag would be created? Fill in each box as a two-digit hex value. C1____? C2____? tag____?
Let the input size of a block cipher be 16 bits and the block cipher is used in the electronic code book (ECB) mode of operation. Suppose we have the following plaintext where all blocks are encrypted using the same key: (02 34 67 88 02 34 44 AB 67 88 B0 3F)hex i) Give an example of a ciphertext if the above plaintext is encrypted using the said block cipher. ii) Let say the encrypted important file is stored in this scheme and each data record has a size of 16 bits. The records are not related to one another. Is ECB mode still appropriate in this scenario? Please state your reason.
In block ciphers, if we use AES for encryption, it does not matter whether the cipher is CBC-based or ECB-based (both will have equally strong results). true or false
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.
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.

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ar cipher(unsigned char block return (key+11"block)%256; e inverse of this cipher is sho ar inv_cipher(unsigned char b 163 is the inverse of 11 mod return (163*(block-key+256))9 ote that the block size is 8 bits