Question

 What is a block cipher?

 What is the equation to describe a block cipher? What is symmetric key encryption and compare with Public key encryption?

 Why is a block cipher considered a keyed permutation? What is the most common block cipher currently in use? Explain the "key schedule"

 Considering the DES algorithm, what Caused it to encounter serious security issues?

 What are Sub-Bytes?

 What is the difference in output when considering ShiftRows

 and MixColumns?

 What is 3DES?

 3DES is the workhorse of which industry and why?

Answer 1

solution:

1.what is block Cipher?

ANS:

Block Cipher Converts the plain text into cipher text by taking plain text's block at a time.

Block cipher uses either 64 bits or more than 64 bits.

2.whats is the equation to describe a block cipher?

Ans:

this is equation

A block cipher is a collection of bisections. Under
a secret key K the cipher encrypts a plaintext block P of length nb into a ciphertext
block C of equal length. Encryption is realized using the encryption function

C = eK(P) : {0, 1}^n → {0, 1}^n

3.what is symmetric key encryption and compare with public key encryption?

Ans:

Symmetric encryption is an encryptionmethodology that uses a single key to encrypt(encode) and decrypt (decode) data. It is the oldest and most well-known technique forencryption. The secret key can be a word, a number, or a string of letters, and it's applied to a message.

Generally, the Symmetric Key Cryptography is known to be faster and simpler. The biggest difference is that symmetric encryption uses the same bit of data — a secret key — to both encrypt and decrypt ,while public key cryptography uses two different keys, one public for encrypting and one private for decrypting.

4. Why a block Cipher considered a keyed permutation?

{0,1}⇤ be an efficient, length-preserving, keyed function. We call F akeyed permutation if for every k, the function Fk(·) is one-to-one. ... The input and output lengths, called theblock size are the same, but the key length may be smaller or larger than the block size.

5. what is most common block cipher currently in use?

DES - DES, which stands for DataEncryption Standard, used to be the most popular block cipher in the world and was used in several industries. It's still popular today, but only because it's usually included in historical discussions of encryption algorithms.

6.Explain the key schedule?

A key schedule is an algorithm that expands a relatively short master key(typi- cally between 40 and 256 bits long) to a relatively large expanded key(typically several hundred or thousand bits) for later use in an encryption and decryption algorithm.

7. Consider the DSE algorithm what cause it to encounter serious security issues?

DES, the Data Encryption Standard, can no longer be considered secure. While no major flaws in its innards are known, it is fundamentally inadequate because its 56-bit key is too short. ... They suggested a minimum of 75 bits to consider an existing cipher secure and a minimum of 90 bits for new ciphers.

8. What are sub-bytes?

SubBytes transform is a simple transform which converts 8bit data to other 8 bit data. For example, 8 bit data "00000000" is transformed into "01100011". What is important is that different byte data are always transformed into different 8 bit data.

9. What are different output when considering shiftrows and mixcolumns?

ShiftRows
In the ShiftRows phase of AES, each row of the 128-bit internal state of the cipher is shifted. The rows in this stage refer to the standard representation of the internal state in AES, which is a 4x4 matrix where each cell contains a byte. Bytes of the internal state are placed in the matrix across rows from left to right and down columns.

MixColumns
Like the ShiftRows phase of AES, the MixColumns phase provides diffusion by mixing the input around. Unlike ShiftRows, MixColumns performs operations splitting the matrix by columns instead of rows.

10. what is 3DES?

What is 3DES? Although it's officially known as the Triple Data Encryption Algorithm (3DEA), it is most commonly referred to as 3DES. This is because the 3DES algorithm uses the Data Encryption Standard (DES) cipher three times to encrypt its data. DES is a symmetric-key algorithm based on a Feistel network.

11. 3DES is a workhouse of which industry and why?

3DES from the time it first promulgated the idea, and this namesake has since come into wide use by most vendors, users, and cryptographers.

The electronic payment industry uses Triple DES and continues to develop and promulgate standards based upon it, such as EMV.

Earlier versions of Microsoft OneNote, Microsoft Outlook 2007 and Microsoft System Center Configuration Manager2012 use Triple DES to password-protect user content and system data. However, in December 2018, Microsoft announced the retirement of 3DES throughout their Office 365 service.

Firefox and Mozilla Thunderbird use Triple DES in CBC mode to encrypt website authentication login credentials when using a master password.